moq-mux 0.5.2

//! H.265 / HEVC.
//!
//! The H.265 analogue of [`crate::codec::h264`]. Parses SPS NAL units
//! and HEVCDecoderConfigurationRecord blobs. The [`Hvc1`] transmuxer
//! rewrites Annex-B input (inline VPS/SPS/PPS) as length-prefixed NALU
//! + out-of-band hvcC. [`Import`] is the Annex-B importer.

mod import;

pub use import::*;

use anyhow::Context;
use bytes::{Buf, BufMut, Bytes, BytesMut};
use scuffle_h265::{NALUnitType, SpsNALUnit};

/// Annex-B → length-prefixed transmuxer; the H.265 analogue of
/// [`crate::codec::h264::Avc1`].
pub struct Hvc1 {
	hvcc: Option<Bytes>,
	vps: Option<Bytes>,
	sps: Option<Bytes>,
	pps: Option<Bytes>,
}

impl Default for Hvc1 {
	fn default() -> Self {
		Self::new()
	}
}

impl Hvc1 {
	/// Build a new transform for a hev1 source.
	pub fn new() -> Self {
		Self {
			hvcc: None,
			vps: None,
			sps: None,
			pps: None,
		}
	}

	/// The HEVCDecoderConfigurationRecord, available once VPS+SPS+PPS have been observed.
	pub fn hvcc(&self) -> Option<&Bytes> {
		self.hvcc.as_ref()
	}

	/// Convert one decoded frame's payload to the hvc1 wire shape.
	///
	/// Returns:
	/// - `Ok(Some(payload))` if a length-prefixed sample is ready to emit.
	/// - `Ok(None)` if the input contained only parameter sets and the
	///   transform is still waiting for slice NALs (hvcC may have been
	///   built as a side effect).
	pub fn transform(&mut self, payload: Bytes) -> anyhow::Result<Option<Bytes>> {
		let mut buf = payload.clone();
		let mut nal_iter = crate::codec::annexb::NalIterator::new(&mut buf);

		let mut out = BytesMut::with_capacity(payload.remaining());
		let mut params_changed = false;
		let mut emitted_any_slice = false;

		loop {
			let nal = match nal_iter.next() {
				Some(Ok(n)) => n,
				Some(Err(e)) => return Err(e),
				None => break,
			};
			if self.process_nal(&nal, &mut out, &mut params_changed)? {
				emitted_any_slice = true;
			}
		}

		if let Some(nal) = nal_iter.flush()? {
			let was_slice = self.process_nal(&nal, &mut out, &mut params_changed)?;
			if was_slice {
				emitted_any_slice = true;
			}
		}

		if params_changed {
			self.rebuild_hvcc()?;
		}

		if !emitted_any_slice {
			return Ok(None);
		}

		Ok(Some(out.freeze()))
	}

	fn process_nal(&mut self, nal: &Bytes, out: &mut BytesMut, params_changed: &mut bool) -> anyhow::Result<bool> {
		if nal.is_empty() {
			return Ok(false);
		}
		// HEVC NAL header is 2 bytes; type is bits 1..=6 of byte 0.
		let nal_unit_type = (nal[0] >> 1) & 0x3f;
		let nal_type = NALUnitType::from(nal_unit_type);

		match nal_type {
			NALUnitType::VpsNut => {
				if self.vps.as_deref() != Some(nal.as_ref()) {
					self.vps = Some(nal.clone());
					*params_changed = true;
				}
				Ok(false)
			}
			NALUnitType::SpsNut => {
				if self.sps.as_deref() != Some(nal.as_ref()) {
					self.sps = Some(nal.clone());
					*params_changed = true;
				}
				Ok(false)
			}
			NALUnitType::PpsNut => {
				if self.pps.as_deref() != Some(nal.as_ref()) {
					self.pps = Some(nal.clone());
					*params_changed = true;
				}
				Ok(false)
			}
			_ => {
				let len = u32::try_from(nal.len()).context("NAL too large for 4-byte length prefix")?;
				out.extend_from_slice(&len.to_be_bytes());
				out.extend_from_slice(nal);
				Ok(true)
			}
		}
	}

	fn rebuild_hvcc(&mut self) -> anyhow::Result<()> {
		let (Some(vps), Some(sps), Some(pps)) = (&self.vps, &self.sps, &self.pps) else {
			return Ok(());
		};
		self.hvcc = Some(build_hvcc(vps, sps, pps)?);
		Ok(())
	}
}

/// Build an HEVCDecoderConfigurationRecord (ISO/IEC 14496-15 §8.3.3).
/// Single-layer streams only.
pub(crate) fn build_hvcc(vps_nal: &[u8], sps_nal: &[u8], pps_nal: &[u8]) -> anyhow::Result<Bytes> {
	for (label, nal) in [("VPS", vps_nal), ("SPS", sps_nal), ("PPS", pps_nal)] {
		anyhow::ensure!(
			nal.len() <= u16::MAX as usize,
			"{} too large for hvcC length field ({} > {})",
			label,
			nal.len(),
			u16::MAX
		);
	}

	let sps = SpsNALUnit::parse(&mut &sps_nal[..]).context("failed to parse SPS NAL unit for hvcC")?;
	let profile = &sps.rbsp.profile_tier_level.general_profile;
	let level_idc = profile.level_idc.context("missing level_idc in SPS")?;
	let constraint_flags = pack_constraint_flags(profile);
	let compat = profile.profile_compatibility_flag.bits().to_be_bytes();
	let num_temporal_layers = sps.rbsp.sps_max_sub_layers_minus1 + 1;

	let mut out = BytesMut::with_capacity(23 + vps_nal.len() + sps_nal.len() + pps_nal.len() + 9 * 3);
	out.put_u8(1); // configurationVersion
	out.put_u8(((profile.profile_space & 0x3) << 6) | ((profile.tier_flag as u8) << 5) | (profile.profile_idc & 0x1f));
	out.put_slice(&compat);
	out.put_slice(&constraint_flags);
	out.put_u8(level_idc);
	out.put_u16(0xf000); // min_spatial_segmentation_idc unknown
	out.put_u8(0xfc); // parallelismType mixed
	out.put_u8(0xfc | (sps.rbsp.chroma_format_idc & 0x3));
	out.put_u8(0xf8 | (sps.rbsp.bit_depth_luma_minus8 & 0x7));
	out.put_u8(0xf8 | (sps.rbsp.bit_depth_chroma_minus8 & 0x7));
	out.put_u16(0); // avgFrameRate unspecified
	out.put_u8(((num_temporal_layers & 0x7) << 3) | ((sps.rbsp.sps_temporal_id_nesting_flag as u8) << 2) | 0x3);
	out.put_u8(3); // numOfArrays

	for (nal_type, nal) in [
		(u8::from(NALUnitType::VpsNut), vps_nal),
		(u8::from(NALUnitType::SpsNut), sps_nal),
		(u8::from(NALUnitType::PpsNut), pps_nal),
	] {
		out.put_u8(0x80 | (nal_type & 0x3f)); // array_completeness = 1
		out.put_u16(1); // numNalus
		out.put_u16(nal.len() as u16);
		out.put_slice(nal);
	}

	Ok(out.freeze())
}

/// Pack the constraint flags from ITU H.265 V10 §7.3.3 Profile, tier and level syntax.
pub(crate) fn pack_constraint_flags(profile: &scuffle_h265::Profile) -> [u8; 6] {
	let mut flags = [0u8; 6];
	flags[0] = ((profile.progressive_source_flag as u8) << 7)
		| ((profile.interlaced_source_flag as u8) << 6)
		| ((profile.non_packed_constraint_flag as u8) << 5)
		| ((profile.frame_only_constraint_flag as u8) << 4);
	flags
}