ffcine-assembly 0.4.0

//! Runs a [`Plan`]: renders segments missing from the cache, joins them by stream copy, mixes
//! the audio, and muxes the master.
//!
//! Cache layout (`<cache>/`): `seg/<key>.mp4` (one per segment), `audio/<key>-aac<bitrate>.m4a`
//! (the mix, encoded), `tmp/` (intermediates). Every entry is written to a `.partial-<pid>` file and
//! renamed when complete, so a killed render resumes: the next run reuses what finished. Nothing is pruned, and old masters are never touched.
//!
//! Shots go through the GPU [`Pipeline`] (decode, grade, scale, encode). The audio is
//! `ffcine_audio::render_audio`'s mix, encoded once. The joins, retime prep, dissolve blends, AAC
//! encode and mux use the `ffmpeg` CLI.

use std::ffi::OsString;
use std::fmt::Write as _;
use std::path::{Path, PathBuf};
use std::process::Command;
use std::time::{Duration, Instant};

use std::sync::Arc;

use ffcine_comp::Base;
use ffcine_render::{
    Backend, Codec, Decode, Device, EncoderSettings, Grade, Hook, Layer, LayerSource, Lut,
    LutStage, LutType, Overlay, ParamTrack, Pipeline, Rational, Size, shaders,
};
use serde_json::json;

use crate::comp::Finish;
use crate::plan::{AudioPlan, Plan, Segment, Shot, TextLayer};
use crate::recipe::{Fingerprinter as _, Key};
use ffcine_render::Warp;
use ffcine_stabilize::{Detection, SourceRange};

/// Errors from [`Renderer::render`].
#[derive(Debug, thiserror::Error)]
pub enum ExecError {
    #[error("{0}")]
    Render(#[from] ffcine_core::Error),
    #[error("{what}: {source}")]
    Io {
        what: String,
        source: std::io::Error,
    },
    #[error("grade of {shot:?}: {msg}")]
    Grade { shot: String, msg: String },
    #[error("stabilizing {shot:?}: {msg}")]
    Stabilize { shot: String, msg: String },
    #[error("ffmpeg ({what}) failed: {log}")]
    Ffmpeg { what: String, log: String },
}

pub(crate) type Result<T> = std::result::Result<T, ExecError>;

fn io(what: impl Into<String>) -> impl FnOnce(std::io::Error) -> ExecError {
    let what = what.into();
    move |source| ExecError::Io { what, source }
}

/// How progress is reported.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum Progress {
    /// Lines on stderr.
    #[default]
    Human,
    /// One JSON object per event on stdout.
    Json,
    Quiet,
}

/// What a render did.
#[derive(Debug, Clone, Default, PartialEq)]
pub struct Report {
    pub segments: usize,
    pub rendered: usize,
    pub rendered_frames: i64,
    /// Time spent rendering segments.
    pub render: Duration,
    /// Mixing audio (`None`: cached or no audio).
    pub audio: Option<Duration>,
    /// Muxing the master (`None`: already up to date).
    pub mux: Option<Duration>,
    pub total: Duration,
}

/// Renders plans against a cache directory.
pub struct Renderer<'a> {
    pub backend: &'a dyn Backend,
    pub cache: PathBuf,
    pub ffmpeg: OsString,
    pub device: Device,
    pub decode: Decode,
    pub progress: Progress,
    /// Builds the GPU grade for a shot's resolved params (LUT, look hook, sharpen); the size is
    /// set by the renderer. `None`: the LUT and sharpen only.
    pub grader: Option<&'a Grader<'a>>,
    /// Stabilizer motion detect on the GPU (NVOF, cached on disk): a source file and range to
    /// per-frame motions. Required by stabilized clips; there is no CPU fallback.
    pub detect: Option<&'a Detector<'a>>,
}

/// See [`Renderer::grader`].
pub type Grader<'g> = dyn Fn(&Shot) -> std::result::Result<Grade, String> + 'g;

/// See [`Renderer::detect`].
pub type Detector<'d> = dyn Fn(&Path, &SourceRange) -> std::result::Result<Detection, String> + 'd;

/// The timeline rate as a rational (`23.976...` -> `24000/1001`).
#[allow(clippy::cast_possible_truncation)]
pub fn rational(rate: f64) -> Rational {
    for den in [1, 1001, 1000, 100] {
        let num = rate * f64::from(den);
        if (num - num.round()).abs() < 1e-3 * f64::from(den) / 1000.0_f64.max(1.0) + 1e-6 {
            return Rational {
                num: num.round() as i32,
                den,
            };
        }
    }
    Rational {
        num: (rate * 1000.0).round() as i32,
        den: 1000,
    }
}

#[allow(clippy::cast_precision_loss)]
pub(crate) fn secs(frames: i64, rate: f64) -> f64 {
    frames as f64 / rate
}

/// The prototype's `tmix=frames=n` on CUDA frames at rate `fr`, as `blend_vulkan` steps (a
/// running mean over `n` copies of the stream, copy `j` starting `j` frames later). The input
/// starts `hist` frames before the piece (`hist < n - 1` near the source's start: the first
/// frame is held for the rest), so the output's first frame averages the `n` frames ending at
/// the piece's first. Ends on CUDA frames for NVENC.
fn blend_filter(n: u32, hist: i64, fr: &str) -> String {
    let pad = i64::from(n) - 1 - hist;
    let mut f = String::new();
    if pad > 0 {
        let _ = write!(f, "tpad=start={pad}:start_mode=clone,");
    }
    let _ = write!(f, "settb=1/({fr}),setpts=N,hwupload,split={n}");
    for j in 0..n {
        let _ = write!(f, "[b{j}]");
    }
    f.push(';');
    for j in 1..n {
        let _ = write!(f, "[b{j}]trim=start_frame={j},setpts=PTS-STARTPTS[t{j}];");
    }
    let mut prev = "b0".to_owned();
    for j in 1..n {
        let _ = write!(
            f,
            "[t{j}][{prev}]blend_vulkan=all_mode=normal:all_opacity={:.7}",
            1.0 / f64::from(j + 1)
        );
        if j + 1 < n {
            prev = format!("m{j}");
            let _ = write!(f, "[{prev}];");
        }
    }
    f.push_str(",hwupload=derive_device=cuda");
    f
}

/// A ramped piece's retime: where to seek (source seconds after the clip's start), how much to
/// read, and the filter giving output frames `from..from + n` of the whole clip.
#[derive(Debug, Clone, PartialEq)]
struct RampCut {
    seek: f64,
    duration: f64,
    filter: String,
}

/// See [`RampCut`]. Source time is read on the source's own clock (`-copyts -start_at_zero`)
/// from the clip's start, so a source frame lands on the same output time whichever piece
/// decodes it, and `fps` numbers output frames from the clip's start: a piece seeks to just
/// before its first source frame and gets the frames the whole clip would have there.
#[allow(clippy::cast_precision_loss)]
fn ramp_cut(ramp: &crate::plan::Ramp, clip_start: f64, from: i64, n: i64, rate: f64) -> RampCut {
    let r = rational(rate);
    // Half a second covers any source frame interval before the first one needed.
    let seek = (ramp.source_time(secs(from, rate)) - 0.5).max(0.0);
    RampCut {
        seek,
        duration: ramp.source_duration - seek + secs(2, rate),
        filter: format!(
            "{},fps={}/{},trim=start_pts={from}:end_pts={},setpts=PTS-STARTPTS",
            ramp.setpts_of(&format!("(PTS*TB-{clip_start})")),
            r.num,
            r.den,
            from + n
        ),
    }
}

impl Renderer<'_> {
    fn dir(&self, sub: &str) -> Result<PathBuf> {
        let d = self.cache.join(sub);
        std::fs::create_dir_all(&d).map_err(io(format!("creating {}", d.display())))?;
        Ok(d)
    }

    pub(crate) fn event(&self, v: &serde_json::Value, human: impl FnOnce() -> String) {
        match self.progress {
            Progress::Human => eprintln!("{}", human()),
            Progress::Json => println!("{v}"),
            Progress::Quiet => {}
        }
    }

    fn ffmpeg(&self, what: &str, args: &[OsString]) -> Result<()> {
        let out = Command::new(&self.ffmpeg)
            .args(["-hide_banner", "-nostdin", "-loglevel", "error", "-y"])
            .args(args)
            .output()
            .map_err(io(format!("running {}", self.ffmpeg.to_string_lossy())))?;
        if out.status.success() {
            Ok(())
        } else {
            let log = String::from_utf8_lossy(&out.stderr);
            let tail: Vec<&str> = log.lines().rev().take(8).collect();
            Err(ExecError::Ffmpeg {
                what: what.into(),
                log: tail.into_iter().rev().collect::<Vec<_>>().join("\n"),
            })
        }
    }

    /// Runs `make(partial)` unless `path` exists, then renames the partial into place.
    fn atomic(path: &Path, make: impl FnOnce(&Path) -> Result<()>) -> Result<bool> {
        if path.exists() {
            return Ok(false);
        }
        let ext = path.extension().and_then(|e| e.to_str()).unwrap_or("mkv");
        // Per process, so two renders making the same file don't write one partial.
        let partial = path.with_extension(format!("partial-{}.{ext}", std::process::id()));
        if let Err(e) = make(&partial) {
            let _ = std::fs::remove_file(&partial);
            return Err(e);
        }
        std::fs::rename(&partial, path).map_err(io(format!("renaming {}", partial.display())))?;
        Ok(true)
    }

    /// Renders `plan` to `output` (an `.mp4`); writes `<output>.ffcine.json` next to it.
    #[allow(clippy::too_many_lines)]
    pub fn render(
        &self,
        plan: &Plan,
        mut text: Option<&mut TextLayer>,
        output: &Path,
    ) -> Result<Report> {
        let t0 = Instant::now();
        if self.cache.is_relative() {
            let cwd = std::env::current_dir().map_err(io("current directory"))?;
            return Renderer {
                cache: cwd.join(&self.cache),
                ffmpeg: self.ffmpeg.clone(),
                ..*self
            }
            .render(plan, text, output);
        }
        let mut report = Report {
            segments: plan.segments.len(),
            ..Report::default()
        };
        if let Some(t) = text.as_deref_mut() {
            let a = &plan.profile.aspect;
            let safe = a.default_safe_area();
            #[allow(clippy::cast_possible_truncation)]
            t.set_profile(
                &a.name,
                [safe.top, safe.right, safe.bottom, safe.left].map(|v| v as f32),
            );
        }
        let manifest_path = manifest_path(output);
        let master_key = plan.master_key();
        if output.exists() && read_manifest_key(&manifest_path).as_ref() == Some(&master_key) {
            self.event(&json!({"event": "up_to_date"}), || {
                format!("{}: up to date", output.display())
            });
            report.total = t0.elapsed();
            return Ok(report);
        }

        let seg_dir = self.dir("seg")?;
        let mut files = Vec::new();
        let n = plan.segments.len();
        for (i, s) in plan.segments.iter().enumerate() {
            let path = seg_dir.join(format!("{}.mp4", s.key));
            let t = Instant::now();
            let made = Self::atomic(&path, |tmp| {
                #[allow(clippy::cast_precision_loss)]
                let overlays = match text.as_deref_mut() {
                    Some(t) => t.overlays(
                        s.start as f64 / plan.rate,
                        u64::try_from(s.frames).unwrap_or(0),
                        plan.rate,
                        plan.profile.size,
                    )?,
                    None => Vec::new(),
                };
                self.segment(plan, s, overlays, tmp)
            })?;
            let el = t.elapsed();
            if made {
                report.rendered += 1;
                report.rendered_frames += s.frames;
                report.render += el;
            }
            self.event(
                &json!({"event": "segment", "i": i + 1, "n": n, "name": s.name, "key": s.key,
                        "frames": s.frames, "status": if made { "rendered" } else { "cached" },
                        "secs": el.as_secs_f64()}),
                || {
                    format!(
                        "[{}/{n}] {} {} ({}f){}",
                        i + 1,
                        if made { "rendered" } else { "cached  " },
                        s.name,
                        s.frames,
                        if made {
                            format!(" in {:.1} s", el.as_secs_f64())
                        } else {
                            String::new()
                        }
                    )
                },
            );
            files.push(path);
        }

        let audio = match &plan.audio {
            Some(a) => {
                let path = self
                    .dir("audio")?
                    .join(format!("{}-aac{}.m4a", a.key, plan.profile.audio_bitrate));
                let t = Instant::now();
                let mut level = None;
                if Self::atomic(&path, |tmp| {
                    level = Some(self.mix(plan, a, tmp)?);
                    Ok(())
                })? {
                    report.audio = Some(t.elapsed());
                }
                if let (Some((lufs, tp)), Some(el)) = (level, report.audio) {
                    self.event(
                        &json!({"event": "audio", "key": a.key, "clips": a.clips, "lufs": lufs,
                                "true_peak": tp, "secs": el.as_secs_f64()}),
                        || {
                            format!(
                                "mixed {} audio clips in {:.1} s: {lufs:.1} LUFS, {tp:.1} dBTP",
                                a.clips,
                                el.as_secs_f64()
                            )
                        },
                    );
                }
                Some(path)
            }
            None => None,
        };

        let t = Instant::now();
        self.mux(plan, &files, audio.as_deref(), output)?;
        report.mux = Some(t.elapsed());
        let manifest = json!({
            "master": master_key,
            "program": plan.program_key(),
            "audio": plan.audio.as_ref().map(|a| &a.key),
            "mix": plan.audio.as_ref().map(|a| &a.options),
            "profile": plan.profile.name,
            "segments": plan.segments.iter().map(|s| &s.key).collect::<Vec<_>>(),
        });
        std::fs::write(&manifest_path, format!("{manifest:#}\n"))
            .map_err(io(format!("writing {}", manifest_path.display())))?;
        report.total = t0.elapsed();
        self.event(
            &json!({"event": "done", "rendered": report.rendered, "segments": n,
                    "secs": report.total.as_secs_f64()}),
            || {
                format!(
                    "{}: {} of {n} segments rendered, {:.1} s",
                    output.display(),
                    report.rendered,
                    report.total.as_secs_f64()
                )
            },
        );
        Ok(report)
    }

    fn pipeline(&self, input: &Path, out: &Path, start: f64, frames: i64, rate: f64) -> Pipeline {
        Pipeline::new(input, out)
            .range(
                Duration::from_secs_f64(start.max(0.0)),
                Some(u64::try_from(frames).unwrap_or(0)),
            )
            .frame_rate(rational(rate))
            .device(self.device)
            .decode(self.decode)
    }

    /// Renders one segment to `out` with the profile's encoder: one GPU pass over the piece the
    /// segment lowers to (`lower.rs`), its base as the pass input and its layers over it.
    fn segment(
        &self,
        plan: &Plan,
        seg: &Segment,
        mut overlays: Vec<Overlay>,
        out: &Path,
    ) -> Result<()> {
        let mut temps = Vec::new();
        let r = self.lower(plan, seg, &mut temps).and_then(|(p, ctx)| {
            let (base, start) = match &p.base {
                Base::Black => (self.black(plan, seg.frames, &seg.key, &mut temps)?, 0.0),
                Base::Video { input, start } => (input.clone(), start.as_secs_f64()),
            };
            overlays.extend(p.overlays);
            let pipe = self
                .pipeline(&base, out, start, seg.frames, plan.rate)
                .context(
                    u64::try_from(ctx.0).unwrap_or(0),
                    u64::try_from(ctx.1).unwrap_or(0),
                )
                .grade(p.grade)
                .layers(p.layers)
                .overlays(overlays)
                .encoder(plan.profile.encoder.clone());
            self.run_dv_retry(&pipe, &seg.key)
        });
        for t in temps {
            let _ = std::fs::remove_file(t);
        }
        r
    }

    /// Runs filter nodes (`docs/compositing.md#libavfilter-escape-hatch`) into lossless
    /// intermediates, cached by the node's key (a whole-clip node's is shared by every piece), and
    /// points their layers at them. Nested comps' layers too.
    pub(crate) fn filter_preps(&self, layers: &mut [Layer]) -> Result<()> {
        for l in layers {
            match &l.source {
                LayerSource::Filtered(p) => {
                    let p = Arc::clone(p);
                    let out = self.dir("prep")?.join(format!(
                        "{}.filter.mkv",
                        Key::of(&json!({"prep": crate::filter_prep::FILTER_PREP, "node": p.key}))
                    ));
                    let what = format!("filter node `{}`", p.graph);
                    Self::atomic(&out, |partial| {
                        let info = self.backend.probe(&p.input)?;
                        let (_, v) = info.video().ok_or_else(|| ExecError::Ffmpeg {
                            what: what.clone(),
                            log: format!("{}: no video stream", p.input.display()),
                        })?;
                        crate::filter_prep::run(
                            &self.ffmpeg,
                            &p,
                            &v.pixel_format,
                            v.color,
                            partial,
                        )
                        .map_err(|log| ExecError::Ffmpeg {
                            what: what.clone(),
                            log,
                        })?;
                        let out = self.backend.probe(partial)?;
                        let got = out.video().map(|(_, v)| (v.width, v.height));
                        crate::filter_prep::check_dims(got, p.dims).map_err(|log| {
                            ExecError::Ffmpeg {
                                what: what.clone(),
                                log,
                            }
                        })?;
                        if !p.free_timing {
                            self.check_frames(partial, p.store.len(), &what)?;
                        }
                        Ok(())
                    })?;
                    let rate = p.rate;
                    l.source = if p.free_timing {
                        LayerSource::Video {
                            input: out,
                            start: Duration::from_secs_f64(secs(
                                i64::try_from(p.show.start).unwrap_or(0),
                                rate,
                            )),
                            map: None,
                        }
                    } else {
                        #[allow(clippy::cast_precision_loss)]
                        let at = (p.show.start as f64 - 0.5) / rate;
                        LayerSource::Video {
                            input: out,
                            start: Duration::from_secs_f64(at.max(0.0)),
                            map: Some((0..i64::try_from(p.show.len()).unwrap_or(0)).collect()),
                        }
                    };
                }
                LayerSource::Scene(s) => {
                    let mut inner = s.layers.clone();
                    self.filter_preps(&mut inner)?;
                    if inner != s.layers {
                        l.source = LayerSource::Scene(Arc::new(ffcine_render::Scene {
                            layers: inner,
                            ..(**s).clone()
                        }));
                    }
                }
                _ => {}
            }
        }
        Ok(())
    }

    /// Fails unless `path`'s video has `want` frames: a graph that drops or adds frames needs
    /// `timing: free`.
    fn check_frames(&self, path: &Path, want: usize, what: &str) -> Result<()> {
        let out = Command::new(&self.ffmpeg)
            .args(["-hide_banner", "-nostdin", "-i"])
            .arg(path)
            .args(["-map", "0:v:0", "-c", "copy", "-f", "null", "-"])
            .output()
            .map_err(io(format!("running {}", self.ffmpeg.to_string_lossy())))?;
        let log = String::from_utf8_lossy(&out.stderr);
        let got = log
            .rsplit("frame=")
            .next()
            .and_then(|s| s.split_whitespace().next())
            .and_then(|n| n.parse::<usize>().ok());
        if got == Some(want) {
            return Ok(());
        }
        Err(ExecError::Ffmpeg {
            what: what.into(),
            log: format!(
                "the graph gave {} frames for {want}: a graph that changes the frame count or \
                 timing needs \"timing\": \"free\" in the layer's filter (the layer then takes \
                 whatever frames it outputs)",
                got.map_or_else(|| "an unknown number of".into(), |n| n.to_string())
            ),
        })
    }

    /// Points remapped video layers whose frame map steps back (reverse, boomerang) at an
    /// all-intra lossless (FFV1) intermediate of the span the map covers, so each step back is one
    /// seek to one frame (`docs/compositing.md#time-remapping`). Nested comps' layers too.
    pub(crate) fn intra_preps(&self, layers: &mut [Layer]) -> Result<()> {
        for l in layers {
            match &mut l.source {
                LayerSource::Video {
                    input,
                    start,
                    map: Some(map),
                } if map.windows(2).any(|w| w[1] < w[0]) => {
                    let frames = map.iter().copied().max().unwrap_or(0) + 1;
                    let at = start.as_secs_f64();
                    let id = json!({
                        // The prep's format: change it when the ffmpeg arguments below change.
                        "prep": INTRA_PREP,
                        "intra": crate::recipe::FsFingerprinter.fingerprint(input),
                        "start": at,
                        "frames": frames,
                    });
                    let prep = self
                        .dir("prep")?
                        .join(format!("{}.intra.mkv", Key::of(&id)));
                    Self::atomic(&prep, |out| {
                        self.ffmpeg("all-intra prep", &intra_prep_args(input, at, frames, out))
                    })?;
                    *input = prep;
                    *start = Duration::ZERO;
                }
                LayerSource::Scene(s) => {
                    let mut inner = s.layers.clone();
                    self.intra_preps(&mut inner)?;
                    if inner != s.layers {
                        *s = Arc::new(ffcine_render::Scene {
                            layers: inner,
                            ..(**s).clone()
                        });
                    }
                }
                _ => {}
            }
        }
        Ok(())
    }

    /// Runs `p`; if it fails, retries once with Dolby Vision RPUs stripped from every source
    /// file (a stream copy): the grade pass can't take them (iPhone HLG).
    fn run_dv_retry(&self, p: &Pipeline, key: &Key) -> Result<()> {
        let Err(e) = p.run(self.backend) else {
            return Ok(());
        };
        let tmp = self.dir("tmp")?;
        let mut stripped = Vec::new();
        let mut strip = |input: &Path, i: usize| -> Option<PathBuf> {
            if input.starts_with(&tmp) {
                return Some(input.to_owned());
            }
            let nodv = tmp.join(format!("{key}.{i}.nodv.mov"));
            let mut v = vec![OsString::from("-i"), input.into()];
            v.extend(args(&[
                "-map",
                "0:v:0",
                "-c:v",
                "copy",
                "-bsf:v",
                "dovi_rpu=strip=1",
            ]));
            v.push(nodv.clone().into());
            self.ffmpeg("strip Dolby Vision", &v).ok()?;
            stripped.push(nodv.clone());
            Some(nodv)
        };
        let mut q = p.clone();
        let mut ok = strip(&p.input, 0).map(|i| q.input = i).is_some();
        for (i, l) in q.layers.iter_mut().enumerate() {
            if let LayerSource::Video { input, .. } = &mut l.source {
                match strip(input, i + 1) {
                    Some(n) => *input = n,
                    None => ok = false,
                }
            }
        }
        let retry = ok && q.run(self.backend).is_ok();
        for f in stripped {
            let _ = std::fs::remove_file(f);
        }
        if retry { Ok(()) } else { Err(e.into()) }
    }

    /// Renders one lowered comp piece to `out` with `encoder` (`ffcine still` of a comp: one
    /// frame, a PNG); `output` overrides the pass's output colour space.
    pub fn render_piece(
        &self,
        piece: &ffcine_comp::Piece,
        rate: f64,
        out: &Path,
        encoder: EncoderSettings,
        output: Option<ffcine_core::ColorSpace>,
    ) -> Result<()> {
        let key = Key::of(&piece.recipe);
        let mut temps = Vec::new();
        let (base, start) = match &piece.base {
            Base::Black => (self.black_at(rate, piece.frames, &key, &mut temps)?, 0.0),
            Base::Video { input, start } => (input.clone(), start.as_secs_f64()),
        };
        let mut layers = piece.layers.clone();
        self.filter_preps(&mut layers)?;
        self.intra_preps(&mut layers)?;
        let mut grade = piece.grade.clone();
        if let Some(c) = output {
            grade.output = c;
        }
        let pipe = self
            .pipeline(&base, out, start, piece.frames, rate)
            .grade(grade)
            .layers(layers)
            .overlays(piece.overlays.clone())
            .encoder(encoder);
        let r = self.run_dv_retry(&pipe, &key);
        for t in temps {
            let _ = std::fs::remove_file(t);
        }
        r
    }

    /// Black, `frames` long, as a base for units without one (gaps, split-screens, whips).
    fn black(
        &self,
        plan: &Plan,
        frames: i64,
        key: &Key,
        temps: &mut Vec<PathBuf>,
    ) -> Result<PathBuf> {
        self.black_at(plan.rate, frames, key, temps)
    }

    /// [`Renderer::black`] at `rate`.
    fn black_at(
        &self,
        rate: f64,
        frames: i64,
        key: &Key,
        temps: &mut Vec<PathBuf>,
    ) -> Result<PathBuf> {
        let black = self.dir("tmp")?.join(format!("{key}.black.mkv"));
        let r = rational(rate);
        self.ffmpeg(
            "black",
            &args(&[
                "-f",
                "lavfi",
                "-i",
                // Tiny: the pass scales it to the frame (backdrops replace it).
                &format!("color=c=black:s=64x36:r={}/{}", r.num, r.den),
                "-frames:v",
                &frames.to_string(),
                "-pix_fmt",
                "yuv420p10le",
                "-color_primaries",
                "bt709",
                "-color_trc",
                "bt709",
                "-colorspace",
                "bt709",
                "-color_range",
                "tv",
                "-c:v",
                "ffv1",
            ])
            .chain([black.clone().into()])
            .collect::<Vec<_>>(),
        )?;
        temps.push(black.clone());
        Ok(black)
    }

    /// A shot's source for the GPU pass: its media at its start, or, with a speed change, a
    /// freeze or a temporal blend, a lossless retimed intermediate (ffmpeg on NVDEC/NVENC) from 0.
    pub(crate) fn input(
        &self,
        plan: &Plan,
        s: &Shot,
        key: &Key,
        tag: &str,
        temps: &mut Vec<PathBuf>,
    ) -> Result<(PathBuf, f64)> {
        self.input_ctx(plan, s, (0, 0), key, tag, temps)
    }

    /// [`Renderer::input`] with `ctx` (before, after) frames of the clip around the piece for
    /// the denoiser ([`Pipeline::context`]): a retimed intermediate holds them too.
    #[allow(clippy::too_many_lines, clippy::many_single_char_names)]
    pub(crate) fn input_ctx(
        &self,
        plan: &Plan,
        s: &Shot,
        ctx: (i64, i64),
        key: &Key,
        tag: &str,
        temps: &mut Vec<PathBuf>,
    ) -> Result<(PathBuf, f64)> {
        // A freeze blends identical frames.
        let blend = s.filters.blend.filter(|_| s.speed.abs() > 1e-9);
        if (s.speed - 1.0).abs() < 1e-9 && s.filters.ramp.is_none() && blend.is_none() {
            return Ok((s.media.clone(), s.start));
        }
        let r = rational(plan.rate);
        let fr = format!("{}/{}", r.num, r.den);
        let prep = self
            .dir("tmp")?
            .join(format!("{key}.{tag}.{}.retime.mkv", s.frames));
        let (before, after) = if s.speed.abs() < 1e-9 { (0, 0) } else { ctx };
        let total = before + s.frames + after;
        let n = total.to_string();
        let mut v = Vec::new();
        if blend.is_some() {
            v.extend(args(&[
                "-init_hw_device",
                "cuda=cu",
                "-init_hw_device",
                "vulkan=vk@cu",
                "-filter_hw_device",
                "vk",
                "-hwaccel_device",
                "cu",
            ]));
        }
        // Frames before the piece a blend averages in.
        let want = blend.map_or(0, |b| i64::from(b) - 1);
        let mut hist = 0;
        let filter = if let Some(ramp) = &s.filters.ramp {
            let from = s.clip_at.max(0) - before;
            hist = want.min(from);
            let cut = ramp_cut(ramp, s.clip_start, from - hist, hist + total, plan.rate);
            v.extend(args(&[
                "-hwaccel",
                "cuda",
                "-hwaccel_output_format",
                "cuda",
                "-copyts",
                "-start_at_zero",
                "-ss",
                &(s.clip_start + cut.seek).to_string(),
                "-t",
                &cut.duration.to_string(),
                "-i",
            ]));
            v.push(s.media.clone().into());
            format!("{},scale_cuda=format=p010le", cut.filter)
        } else if s.speed.abs() < 1e-9 {
            v.extend(args(&["-ss", &s.start.to_string(), "-i"]));
            v.push(s.media.clone().into());
            format!("trim=end_frame=1,loop=loop=-1:size=1:start=0,setpts=N/({fr})/TB,format=p010le")
        } else {
            #[allow(clippy::cast_possible_truncation)]
            let room =
                (s.shifted(-before, plan.rate).start * plan.rate / s.speed + 1e-6).floor() as i64;
            hist = want.min(room.max(0));
            let src = secs(hist + before + s.frames + after + 2, plan.rate) * s.speed;
            // Frames stay in VRAM from NVDEC to the lossless NVENC intermediate: a timelapse
            // reads 20x its length of source.
            v.extend(args(&[
                "-hwaccel",
                "cuda",
                "-hwaccel_output_format",
                "cuda",
                "-ss",
                &s.shifted(-before - hist, plan.rate).start.to_string(),
                "-t",
                &src.to_string(),
                "-i",
            ]));
            v.push(s.media.clone().into());
            format!(
                "setpts=(PTS-STARTPTS)/{},fps={fr},scale_cuda=format=p010le",
                s.speed
            )
        };
        let filter = match blend {
            Some(b) => format!("{filter},{}", blend_filter(b, hist, &fr)),
            None => filter,
        };
        v.extend(args(&[
            "-map",
            "0:v:0",
            "-vf",
            &filter,
            "-frames:v",
            &n,
            "-c:v",
            "hevc_nvenc",
            "-tune",
            "lossless",
        ]));
        v.push(prep.clone().into());
        self.ffmpeg("retime", &v)?;
        temps.push(prep.clone());
        Ok((prep, secs(before, plan.rate)))
    }

    /// A shot's grade at `size`: the grader's (LUT, look, sharpen), its geometry as `pic`
    /// (reframe, stabilizer, and on the main picture the NLE crop and transform), then its finish
    /// with a transition's `mix` folded in.
    pub(crate) fn shot_grade(
        &self,
        s: &Shot,
        plan: &Plan,
        size: Size,
        mix: Option<&Mix>,
        pic: Pic,
    ) -> Result<Grade> {
        let base = match self.grader {
            Some(g) => g(s).map_err(|msg| ExecError::Grade {
                shot: s.name.clone(),
                msg,
            })?,
            None => Self::lut_grade(s)?,
        };
        let mut g = Grade {
            size: Some(size),
            denoise: s.filters.denoise,
            ..base
        };
        let rate = plan.rate;
        let out = if size == plan.profile.size {
            plan.profile.aspect.clone()
        } else {
            ffcine_reframe::Profile {
                width: size.width,
                height: size.height,
                safe_area: None,
                ..plan.profile.aspect.clone()
            }
        };
        self.geometry(plan, s, &mut g, &out, pic)?;
        if let Some(h) = finish_hook(&s.finish, s.clip_at, s.frames, s.clip_frames, rate, mix) {
            g.hooks.push(h);
        }
        Ok(g)
    }

    /// A video file's picture size.
    pub(crate) fn dims(&self, path: &Path) -> Result<(u32, u32)> {
        let info = self.backend.probe(path)?;
        info.video()
            .map(|(_, v)| (v.width, v.height))
            .filter(|(w, h)| *w > 0 && *h > 0)
            .ok_or_else(|| ExecError::Grade {
                shot: path.display().to_string(),
                msg: "no video stream".into(),
            })
    }

    /// The LUT and sharpen of a shot's grade.
    fn lut_grade(s: &Shot) -> Result<Grade> {
        Ok(Grade {
            lut: s
                .lut
                .as_ref()
                .map(|p| {
                    Lut::from_cube_file(p).map(|lut| LutStage {
                        lut,
                        kind: LutType::Normalized,
                    })
                })
                .transpose()?,
            #[allow(clippy::cast_possible_truncation)]
            sharpen: s.grade.sharpen.unwrap_or(0.0) as f32,
            ..Grade::default()
        })
    }

    /// Reframe windows and the stabilizer warp of `s` into `grade`, rendering at `out`'s size;
    /// on the main picture also its NLE crop and transform ([`ffcine_reframe::geo`]; an overlay's
    /// transform places its layer instead). A panel's reframe `focus` sets its window.
    ///
    /// Windows come from the clip's reframe for the profile's aspect, evaluated at the piece's
    /// frames of the whole clip (so punch-ins and pushes run across cuts); without a reframe they
    /// only crop a source of another aspect to the output's. The stabilizer detects over the
    /// source frames the clip's [`Shot::span`] covers (one cached detect for every piece, also
    /// for retimed and ramped clips, whose output frames map to source frames through their
    /// speed), smooths, and keeps this piece's warps.
    #[allow(
        clippy::many_single_char_names,
        clippy::cast_possible_truncation,
        clippy::cast_precision_loss,
        clippy::cast_sign_loss
    )]
    fn geometry(
        &self,
        plan: &Plan,
        s: &Shot,
        grade: &mut Grade,
        out: &ffcine_reframe::Profile,
        pic: Pic,
    ) -> Result<()> {
        let stab = s.filters.stabilize.filter(|_| s.speed.abs() > 1e-9);
        let no_geo = ffcine_reframe::Geo::default();
        let geo = if pic == Pic::Main {
            &s.filters.geo
        } else {
            &no_geo
        };
        let (w, h) = self.dims(&s.media)?;
        if s.filters.reframe.is_none()
            && stab.is_none()
            && geo.is_empty()
            && (f64::from(w) / f64::from(h) - out.aspect()).abs() < 0.01
        {
            return Ok(());
        }
        let mut reframe = s.filters.reframe.clone().unwrap_or_default();
        if pic == Pic::Panel {
            reframe = reframe.focused();
        }
        let shot = ffcine_reframe::Shot {
            width: w,
            height: h,
            frames: s.clip_frames.max(s.clip_at + s.frames).max(1) as u64,
            rate: plan.rate,
            start: s.clip_start,
        };
        let at = |i: i64| (s.clip_at + i).max(0) as u64;
        let mapped: Vec<_> = if geo.is_empty() {
            let windows: Vec<_> = (0..s.frames)
                .map(|i| reframe.frame(at(i), &shot, out))
                .collect();
            ffcine_reframe::pass::apply(grade, &windows, &[], (w, h), out);
            Vec::new()
        } else {
            (0..s.frames)
                .map(|i| geo.frame(&reframe, at(i), &shot, out).1)
                .collect()
        };
        let Some(params) = stab else {
            if !mapped.is_empty() {
                ffcine_reframe::pass::apply_mapped(grade, &mapped, &[], (w, h), out);
            }
            return Ok(());
        };
        let detect = self.detect.ok_or_else(|| ExecError::Stabilize {
            shot: s.name.clone(),
            msg: "needs the GPU motion detect (NVOF)".into(),
        })?;
        // Source seconds since the clip's first frame for clip frame `k` (timeline frames).
        let src = |k: i64| -> f64 {
            let t = secs(k, plan.rate);
            match &s.filters.ramp {
                Some(r) => r.source_time(t),
                None => t * s.speed,
            }
        };
        let (lo, hi) = s.span;
        let first = src(lo.max(0));
        let last = src(hi) + secs(1, plan.rate);
        let range = SourceRange {
            start: (s.clip_start + first).max(0.0),
            frames: ((last - first) * plan.rate).ceil().max(1.0) as usize,
            rate: rational(plan.rate),
        };
        let det = detect(&s.media, &range).map_err(|msg| ExecError::Stabilize {
            shot: s.name.clone(),
            msg,
        })?;
        let st = ffcine_stabilize::stabilize(&det, &params);
        let n = st.transforms.len();
        let transforms = (0..s.frames)
            .filter_map(|i| {
                let k = ((src((s.clip_at + i).max(0)) - first) * plan.rate).round();
                st.transforms
                    .get((k.max(0.0) as usize).min(n.saturating_sub(1)))
                    .copied()
            })
            .collect();
        if mapped.is_empty() {
            grade.warp = Some(Warp { transforms });
        } else {
            ffcine_reframe::pass::apply_mapped(grade, &mapped, &transforms, (w, h), out);
        }
        Ok(())
    }

    /// Mixes the audio (`ffcine_audio::stream_audio`, the picture's length) and encodes it to
    /// AAC. Returns the master's loudness and true peak.
    fn mix(&self, plan: &Plan, a: &AudioPlan, out: &Path) -> Result<(f64, f64)> {
        let tmp = self.dir("tmp")?;
        let mut options = a.options.clone();
        options.scratch = Some(tmp.clone());
        let mut mix = ffcine_audio::stream_audio(&a.timeline, &options, false)?;
        let wav = tmp.join(format!("{}.wav", a.key));
        mix.write_master(&wav)?;
        let mut v = vec![OsString::from("-i"), wav.clone().into()];
        v.extend(args(&[
            "-c:a",
            "aac",
            "-b:a",
            &plan.profile.audio_bitrate.to_string(),
        ]));
        v.push(out.into());
        let r = self.ffmpeg("audio encode", &v);
        let _ = std::fs::remove_file(wav);
        r.map(|()| (mix.lufs, mix.true_peak))
    }

    /// The segments joined by stream copy (concat demuxer) plus the audio, to `output`
    /// (atomic): one pass over the picture.
    fn mux(
        &self,
        plan: &Plan,
        files: &[PathBuf],
        audio: Option<&Path>,
        output: &Path,
    ) -> Result<()> {
        let ext = output.extension().and_then(|e| e.to_str()).unwrap_or("mp4");
        let partial = output.with_extension(format!("partial.{ext}"));
        let list = output.with_extension("partial.txt");
        let body = files.iter().fold(String::new(), |mut s, f| {
            let _ = writeln!(
                s,
                "file '{}'",
                f.display().to_string().replace('\'', r"'\''")
            );
            s
        });
        std::fs::write(&list, body).map_err(io("writing concat list"))?;
        let mut v = args(&["-f", "concat", "-safe", "0", "-i"]).collect::<Vec<_>>();
        v.push(list.clone().into());
        if let Some(a) = audio {
            v.push("-i".into());
            v.push(a.into());
        }
        v.extend(args(&["-map", "0:v", "-c:v", "copy"]));
        if matches!(
            plan.profile.encoder.codec,
            Codec::HevcNvenc | Codec::HevcVulkan | Codec::HevcVaapi | Codec::Libx265
        ) {
            v.extend(args(&["-tag:v", "hvc1"]));
        }
        if audio.is_some() {
            v.extend(args(&["-map", "1:a", "-c:a", "copy"]));
        }
        v.extend(args(&["-movflags", "+faststart"]));
        v.push(partial.clone().into());
        let r = self.ffmpeg("mux", &v);
        let _ = std::fs::remove_file(list);
        r?;
        std::fs::rename(&partial, output).map_err(io(format!("writing {}", output.display())))
    }
}

/// A transition's contribution to a side's finish.
pub(crate) enum Mix {
    /// Per-frame fade towards the colour (1 = the picture).
    Fade(Vec<f32>, [f64; 3]),
    /// Per-frame lift towards white.
    Lift(Vec<f32>),
    /// A split-screen's own `(fade, lift)` tracks and fade colour.
    Both((Vec<f32>, Vec<f32>), [f64; 3]),
}

/// Which picture a shot's grade is for: what its geometry takes ([`Renderer::geometry`]).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum Pic {
    /// The main picture (or a transition's side): reframe, stabilizer, NLE crop and transform.
    Main,
    /// A split-screen panel: reframe (its `focus`) and stabilizer, in the panel.
    Panel,
    /// Picture-in-picture: reframe and stabilizer in the layer; its transform places the layer.
    Overlay,
}

/// No grade but the output size (gaps, backdrops).
pub(crate) fn identity(size: Size) -> Grade {
    Grade {
        size: Some(size),
        ..Grade::default()
    }
}

/// [`shaders::alpha`] with per-frame `opacity` and a fixed corner `radius` in layer pixels.
pub(crate) fn alpha_hook(opacity: Vec<f32>, radius: f64) -> Hook {
    Hook {
        name: "alpha".into(),
        source: shaders::alpha().into(),
        params: vec![("radius".into(), radius)],
        tracks: vec![ParamTrack {
            name: "opacity".into(),
            values: opacity,
        }],
    }
}

/// [`shaders::finish`] for frames `at..at + n` of a clip `len` frames long, with a transition's
/// `mix` folded in; `None` when it would do nothing.
#[allow(clippy::many_single_char_names)]
pub(crate) fn finish_hook(
    f: &Finish,
    at: i64,
    n: i64,
    len: i64,
    rate: f64,
    mix: Option<&Mix>,
) -> Option<Hook> {
    if f.is_identity() && mix.is_none() {
        return None;
    }
    let (mut fade, mut lift) = f.tracks(at, n, len, rate);
    let mut colour = f.fade_colour;
    let mut fold = |k: &[f32], l: &[f32], c: Option<[f64; 3]>| {
        for (i, v) in k.iter().enumerate() {
            if let Some(x) = fade.get_mut(i) {
                *x = x.min(*v);
            }
        }
        for (i, v) in l.iter().enumerate() {
            if let Some(x) = lift.get_mut(i) {
                *x = x.max(*v);
            }
        }
        if let Some(c) = c {
            colour = c;
        }
    };
    match mix {
        Some(Mix::Fade(k, c)) => fold(k, &[], Some(*c)),
        Some(Mix::Both((k, l), c)) if k.iter().any(|v| *v < 1.0) => fold(k, l, Some(*c)),
        Some(Mix::Lift(l) | Mix::Both((_, l), _)) => fold(&[], l, None),
        None => {}
    }
    Some(Hook {
        name: "finish".into(),
        source: shaders::finish().into(),
        params: vec![
            ("darken".into(), f.darken),
            ("vignette".into(), f.vignette_angle()),
            ("fade_r".into(), colour[0]),
            ("fade_g".into(), colour[1]),
            ("fade_b".into(), colour[2]),
        ],
        tracks: vec![
            ParamTrack {
                name: "fade".into(),
                values: fade,
            },
            ParamTrack {
                name: "lift".into(),
                values: lift,
            },
        ],
    })
}

fn args<'a>(a: &'a [&'a str]) -> impl Iterator<Item = OsString> + 'a {
    a.iter().map(OsString::from)
}

/// `<output>.ffcine.json`: keys of what the master was made from.
pub fn manifest_path(output: &Path) -> PathBuf {
    let mut s = output.as_os_str().to_owned();
    s.push(".ffcine.json");
    PathBuf::from(s)
}

fn read_manifest_key(path: &Path) -> Option<Key> {
    let v: serde_json::Value = serde_json::from_str(&std::fs::read_to_string(path).ok()?).ok()?;
    Some(Key(v.get("master")?.as_str()?.to_owned()))
}

/// The all-intra prep's format, in its cache key ([`Renderer::intra_preps`]).
const INTRA_PREP: &str = "ffv1-l3-g1";

/// ffmpeg arguments for an all-intra lossless (FFV1) copy of `frames` frames of `input` from
/// `at` s into `out`. The pixels stay as stored (`-noautorotate`: no transpose on the CPU) and the
/// display matrix, colour tags, bit depth and HDR metadata are carried over, so the decoder
/// turns and tags the prep as it does the source.
fn intra_prep_args(input: &Path, at: f64, frames: i64, out: &Path) -> Vec<OsString> {
    let mut v: Vec<OsString> = args(&["-ss", &at.to_string(), "-noautorotate", "-i"]).collect();
    v.push(input.into());
    v.extend(args(&[
        "-map",
        "0:v:0",
        "-frames:v",
        &frames.to_string(),
        "-fps_mode",
        "passthrough",
        // FFV1: lossless in any pixel format, every frame a keyframe.
        "-c:v",
        "ffv1",
        "-level",
        "3",
        "-g",
        "1",
        "-slices",
        "16",
        "-an",
    ]));
    v.push(out.into());
    v
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::plan::Ramp;

    fn ramp() -> Ramp {
        Ramp {
            points: vec![(0.0, 1.0), (0.5, 3.0), (1.0, 1.0)],
            source_duration: 8.0,
        }
    }

    #[test]
    fn ramp_pieces_seek_to_their_own_source() {
        let rate = 24000.0 / 1001.0;
        let r = ramp();
        let first = ramp_cut(&r, 2.5, 0, 30, rate);
        assert!(first.seek.abs() < 1e-12);
        assert!((first.duration - (8.0 + 2.0 / rate)).abs() < 1e-9);
        assert!(first.filter.contains("(PTS*TB-2.5)"));
        assert!(
            first
                .filter
                .ends_with("fps=24000/1001,trim=start_pts=0:end_pts=30,setpts=PTS-STARTPTS")
        );
        let late = ramp_cut(&r, 2.5, 70, 30, rate);
        let t = r.source_time(70.0 / rate);
        assert!(late.seek > 1.0 && late.seek < t && t - late.seek <= 0.5 + 1e-9);
        assert!((late.duration - (8.0 - late.seek + 2.0 / rate)).abs() < 1e-9);
        assert!(late.filter.contains("trim=start_pts=70:end_pts=100,"));
    }

    fn ffmpeg(args: &[&str]) -> Vec<u8> {
        let out = Command::new("ffmpeg")
            .args(["-v", "error", "-y"])
            .args(args)
            .output()
            .expect("ffmpeg on PATH");
        assert!(
            out.status.success(),
            "{}",
            String::from_utf8_lossy(&out.stderr)
        );
        out.stdout
    }

    /// Per-frame hashes of a ramped piece, the way `input` cuts it (on the CPU).
    fn ramp_piece(src: &Path, from: i64, n: i64) -> Vec<String> {
        let rate = 24000.0 / 1001.0;
        let clip_start = 1.0;
        let c = ramp_cut(&ramp(), clip_start, from, n, rate);
        let out = ffmpeg(&[
            "-copyts",
            "-start_at_zero",
            "-ss",
            &(clip_start + c.seek).to_string(),
            "-t",
            &c.duration.to_string(),
            "-i",
            src.to_str().expect("utf-8"),
            "-vf",
            &c.filter,
            "-frames:v",
            &n.to_string(),
            "-f",
            "framemd5",
            "-",
        ]);
        String::from_utf8_lossy(&out)
            .lines()
            .filter(|l| !l.starts_with('#'))
            .map(|l| l.rsplit(',').next().unwrap_or("").trim().to_owned())
            .collect()
    }

    #[test]
    #[ignore = "needs ffmpeg"]
    fn ramp_pieces_match_the_whole_clip() {
        let d = std::env::temp_dir().join(format!("ffcine-ramp-{}", std::process::id()));
        std::fs::create_dir_all(&d).expect("temp dir");
        let src = d.join("src.mp4");
        ffmpeg(&[
            "-f",
            "lavfi",
            "-i",
            "testsrc2=size=160x90:rate=30000/1001",
            "-t",
            "10",
            "-g",
            "15",
            "-c:v",
            "libx264",
            "-qp",
            "0",
            src.to_str().expect("utf-8"),
        ]);
        let whole = ramp_piece(&src, 0, 100);
        assert_eq!(whole.len(), 100);
        let distinct: std::collections::HashSet<_> = whole.iter().collect();
        assert!(distinct.len() > 90, "the source's frames all differ");
        for (from, n) in [(0, 17), (17, 40), (57, 3), (60, 40)] {
            let piece = ramp_piece(&src, from, n);
            let (a, b) = (
                usize::try_from(from).unwrap(),
                usize::try_from(from + n).unwrap(),
            );
            assert_eq!(piece, whole[a..b], "piece {from}+{n}");
        }
        let _ = std::fs::remove_dir_all(&d);
    }

    /// `ffprobe` of `p`'s first video stream: size, pixel format, colour tags, rotation.
    fn probe(p: &Path) -> String {
        let out = Command::new("ffprobe")
            .args(["-v", "error", "-select_streams", "v:0", "-show_entries"])
            .args([
                "stream=width,height,pix_fmt,color_range,color_space,color_transfer,\
                 color_primaries:stream_side_data=rotation,max_content,max_luminance",
                "-of",
                "compact",
            ])
            .arg(p)
            .output()
            .expect("ffprobe on PATH");
        String::from_utf8_lossy(&out.stdout).trim().to_owned()
    }

    #[test]
    #[ignore = "needs ffmpeg"]
    fn intra_prep_keeps_pixels_rotation_and_colour() {
        let d = std::env::temp_dir().join(format!("ffcine-intra-{}", std::process::id()));
        std::fs::create_dir_all(&d).expect("temp dir");
        let (hdr, src, prep) = (d.join("hdr.mkv"), d.join("rot.mkv"), d.join("prep.mkv"));
        let s = |p: &Path| p.to_str().expect("utf-8").to_owned();
        // A 10-bit PQ / BT.2020 source with HDR10 metadata and a 90° display matrix.
        ffmpeg(&[
            "-f",
            "lavfi",
            "-i",
            "testsrc2=s=320x180:r=30:d=1",
            "-vf",
            "format=yuv420p10le,setparams=color_primaries=bt2020:color_trc=smpte2084:\
             colorspace=bt2020nc:range=tv",
            "-c:v",
            "libx265",
            "-x265-params",
            "log-level=none:keyint=15:hdr10=1:max-cll=1000,400:\
             master-display=G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(10000000,1)",
            &s(&hdr),
        ]);
        ffmpeg(&[
            "-display_rotation",
            "90",
            "-i",
            &s(&hdr),
            "-c",
            "copy",
            &s(&src),
        ]);
        let at = 10.0 / 30.0;
        let mut argv = vec![OsString::from("-v"), "error".into(), "-y".into()];
        argv.extend(intra_prep_args(&src, at, 12, &prep));
        let st = Command::new("ffmpeg").args(&argv).status().expect("ffmpeg");
        assert!(st.success());
        let (was, got) = (probe(&src), probe(&prep));
        for want in [
            "width=320",
            "height=180",
            "pix_fmt=yuv420p10le",
            "color_range=tv",
            "color_space=bt2020nc",
            "color_transfer=smpte2084",
            "color_primaries=bt2020",
            "rotation=90",
        ] {
            assert!(was.contains(want), "source {want}: {was}");
            assert!(got.contains(want), "prep {want}: {got}");
        }
        // HEVC carries HDR10 metadata per frame (SEI); the prep has it on the stream.
        assert!(
            got.contains("max_content=1000"),
            "prep HDR10 metadata: {got}"
        );
        // The stored (unrotated) pixels of frames 10..22, bit for bit.
        let md5 = |p: &Path, ss: Option<f64>, n: &str| -> Vec<String> {
            let mut argv: Vec<String> = Vec::new();
            if let Some(secs) = ss {
                argv.extend(["-ss".into(), secs.to_string()]);
            }
            argv.extend(["-noautorotate", "-i"].map(String::from));
            argv.push(s(p));
            argv.extend(["-frames:v", n, "-f", "framemd5", "-"].map(String::from));
            let refs: Vec<&str> = argv.iter().map(String::as_str).collect();
            String::from_utf8_lossy(&ffmpeg(&refs))
                .lines()
                .filter(|l| !l.starts_with('#'))
                .map(|l| l.rsplit(',').next().unwrap_or("").trim().to_owned())
                .collect()
        };
        let want = md5(&src, Some(at), "12");
        assert_eq!(want.len(), 12);
        assert_eq!(md5(&prep, None, "12"), want);
        let _ = std::fs::remove_dir_all(&d);
    }

    #[test]
    fn blend_chain() {
        assert_eq!(
            blend_filter(3, 2, "24000/1001"),
            "settb=1/(24000/1001),setpts=N,hwupload,split=3[b0][b1][b2];\
             [b1]trim=start_frame=1,setpts=PTS-STARTPTS[t1];\
             [b2]trim=start_frame=2,setpts=PTS-STARTPTS[t2];\
             [t1][b0]blend_vulkan=all_mode=normal:all_opacity=0.5000000[m1];\
             [t2][m1]blend_vulkan=all_mode=normal:all_opacity=0.3333333,\
             hwupload=derive_device=cuda"
        );
        // Near the source's start the first frame stands in for the missing history.
        let f = blend_filter(2, 0, "24");
        assert!(f.starts_with("tpad=start=1:start_mode=clone,settb=1/(24),"));
        assert!(f.contains("[t1][b0]blend_vulkan=all_mode=normal:all_opacity=0.5000000,hwupload"));
    }

    #[test]
    fn rates() {
        assert_eq!(
            rational(24000.0 / 1001.0),
            Rational {
                num: 24000,
                den: 1001
            }
        );
        assert_eq!(
            rational(23.976_023_976_023_978),
            Rational {
                num: 24000,
                den: 1001
            }
        );
        assert_eq!(rational(25.0), Rational { num: 25, den: 1 });
        assert_eq!(
            rational(60000.0 / 1001.0),
            Rational {
                num: 60000,
                den: 1001
            }
        );
    }
}