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extern crate ffmpeg_the_third as ffmpeg;
use std::path::Path;
use ffmpeg::{
codec::{decoder, packet},
format,
format::context,
frame,
media::Type,
};
use ffmpeg_the_third::threading;
use num_rational::Rational32;
use v_frame::{
frame::Frame,
pixel::{ChromaSampling, Pixel},
};
use crate::{error::DecoderError, VideoDetails};
/// An interface that is used for decoding a video stream using ffmpeg
///
/// There have been desync issue reported with this decoder
/// on some video files. Use at your own risk!
pub struct FfmpegDecoder {
input_ctx: context::Input,
decoder: decoder::Video,
pub(crate) video_details: VideoDetails,
stream_index: usize,
end_of_stream: bool,
eof_sent: bool,
}
impl FfmpegDecoder {
/// Creates a new FFmpeg decoder for the specified video file.
///
/// This function initializes the FFmpeg library, opens the input video file,
/// finds the best video stream, and sets up a video decoder with frame-level
/// threading for optimal performance.
///
/// # Arguments
///
/// * `input` - A path to the video file to decode. Can be any type that implements
/// `AsRef<Path>`, such as `&str`, `String`, `PathBuf`, or `&Path`.
///
/// # Returns
///
/// Returns `Ok(FfmpegDecoder)` on success, containing a configured decoder ready
/// to read video frames. The decoder will have its video details populated with
/// information extracted from the input file.
///
/// # Errors
///
/// This function can return several types of errors:
///
/// * `DecoderError::FfmpegInternalError` - If FFmpeg initialization fails or
/// if there's an internal FFmpeg error during codec context setup
/// * `DecoderError::FileReadError` - If the input file cannot be opened or read
/// * `DecoderError::NoVideoStream` - If no video stream is found in the input file
/// * `DecoderError::UnsupportedFormat` - If the video format is not supported.
/// Currently supports YUV 4:2:0, 4:2:2, and 4:4:4 with 8, 10, or 12-bit depth
///
/// # Supported Formats
///
/// The decoder currently supports the following pixel formats:
/// - YUV420P, YUV422P, YUV444P (8-bit)
/// - YUVJ420P, YUVJ422P, YUVJ444P (8-bit JPEG colorspace)
/// - YUV420P10LE, YUV422P10LE, YUV444P10LE (10-bit)
/// - YUV420P12LE, YUV422P12LE, YUV444P12LE (12-bit)
///
/// # Threading
///
/// The decoder is configured with frame-level threading for improved performance
/// on multi-core systems.
///
/// # Examples
///
/// ```rust,no_run
/// use av_decoders::FfmpegDecoder;
///
/// // Create decoder from string path
/// let decoder = FfmpegDecoder::new("input.mp4")?;
///
/// // Create decoder from PathBuf
/// use std::path::PathBuf;
/// let path = PathBuf::from("input.mkv");
/// let decoder = FfmpegDecoder::new(&path)?;
/// # Ok::<(), av_decoders::DecoderError>(())
/// ```
///
/// # Warning
///
/// There have been desync issues reported with this decoder on some video files.
/// Use at your own risk for critical applications.
#[inline]
pub fn new<P: AsRef<Path>>(input: P) -> Result<Self, DecoderError> {
ffmpeg::init().map_err(|e| DecoderError::FfmpegInternalError {
cause: e.to_string(),
})?;
let input_ctx = format::input(&input).map_err(|e| DecoderError::FileReadError {
cause: e.to_string(),
})?;
let input = input_ctx
.streams()
.best(Type::Video)
.ok_or(DecoderError::NoVideoStream)?;
let stream_index = input.index();
let mut context = ffmpeg::codec::context::Context::from_parameters(input.parameters())
.map_err(|e| DecoderError::FfmpegInternalError {
cause: e.to_string(),
})?;
context.set_threading(threading::Config::kind(threading::Type::Frame));
let mut decoder = context
.decoder()
.video()
.map_err(|_| DecoderError::NoVideoStream)?;
decoder.set_parameters(input.parameters()).map_err(|e| {
DecoderError::FfmpegInternalError {
cause: e.to_string(),
}
})?;
let total_frames = input.frames();
let frame_rate = input.rate();
Ok(Self {
video_details: VideoDetails {
width: decoder.width() as usize,
height: decoder.height() as usize,
bit_depth: match decoder.format() {
format::pixel::Pixel::YUV420P
| format::pixel::Pixel::YUV422P
| format::pixel::Pixel::YUV444P
| format::pixel::Pixel::YUVJ420P
| format::pixel::Pixel::YUVJ422P
| format::pixel::Pixel::YUVJ444P => 8,
format::pixel::Pixel::YUV420P10LE
| format::pixel::Pixel::YUV422P10LE
| format::pixel::Pixel::YUV444P10LE => 10,
format::pixel::Pixel::YUV420P12LE
| format::pixel::Pixel::YUV422P12LE
| format::pixel::Pixel::YUV444P12LE => 12,
fmt => {
return Err(DecoderError::UnsupportedFormat {
fmt: format!("{fmt:?}"),
});
}
},
chroma_sampling: match decoder.format() {
format::pixel::Pixel::YUV420P
| format::pixel::Pixel::YUVJ420P
| format::pixel::Pixel::YUV420P10LE
| format::pixel::Pixel::YUV420P12LE => ChromaSampling::Cs420,
format::pixel::Pixel::YUV422P
| format::pixel::Pixel::YUVJ422P
| format::pixel::Pixel::YUV422P10LE
| format::pixel::Pixel::YUV422P12LE => ChromaSampling::Cs422,
format::pixel::Pixel::YUV444P
| format::pixel::Pixel::YUVJ444P
| format::pixel::Pixel::YUV444P10LE
| format::pixel::Pixel::YUV444P12LE => ChromaSampling::Cs444,
fmt => {
return Err(DecoderError::UnsupportedFormat {
fmt: format!("{fmt:?}"),
});
}
},
frame_rate: Rational32::new(frame_rate.numerator(), frame_rate.denominator()),
total_frames: total_frames.try_into().ok(),
},
decoder,
input_ctx,
stream_index,
end_of_stream: false,
eof_sent: false,
})
}
fn decode_frame<T: Pixel>(&self, decoded: &frame::Video) -> Frame<T> {
const SB_SIZE_LOG2: usize = 6;
const SB_SIZE: usize = 1 << SB_SIZE_LOG2;
const SUBPEL_FILTER_SIZE: usize = 8;
const FRAME_MARGIN: usize = 16 + SUBPEL_FILTER_SIZE;
const LUMA_PADDING: usize = SB_SIZE + FRAME_MARGIN;
let mut f: Frame<T> = Frame::new_with_padding(
self.video_details.width,
self.video_details.height,
self.video_details.chroma_sampling,
LUMA_PADDING,
);
let width = self.video_details.width;
let height = self.video_details.height;
let bit_depth = self.video_details.bit_depth;
let bytes = if bit_depth > 8 { 2 } else { 1 };
let (chroma_width, _) = self
.video_details
.chroma_sampling
.get_chroma_dimensions(width, height);
f.planes[0].copy_from_raw_u8(decoded.data(0), width * bytes, bytes);
f.planes[1].copy_from_raw_u8(decoded.data(1), chroma_width * bytes, bytes);
f.planes[2].copy_from_raw_u8(decoded.data(2), chroma_width * bytes, bytes);
f
}
pub(crate) fn read_video_frame<T: Pixel>(
&mut self,
frame_index: usize,
) -> Result<Frame<T>, DecoderError> {
// For some reason there's a crap ton of work needed to get ffmpeg to do
// something simple, because each codec has it's own stupid way of doing
// things and they don't all decode the same way.
//
// Maybe ffmpeg could have made a simple, singular interface that does this for
// us, but noooooo.
//
// Reference: https://ffmpeg.org/doxygen/trunk/api-h264-test_8c_source.html#l00110
loop {
// This iterator is actually really stupid... it doesn't reset itself after each
// `new`. But that solves our lifetime hell issues, ironically.
let packet = self
.input_ctx
.packets()
.next()
.and_then(Result::ok)
.map(|(_, packet)| packet);
let mut packet = if let Some(packet) = packet {
packet
} else {
self.end_of_stream = true;
packet::Packet::empty()
};
if self.end_of_stream && !self.eof_sent {
let _ = self.decoder.send_eof();
self.eof_sent = true;
}
if self.end_of_stream || packet.stream() == self.stream_index {
let mut decoded = frame::Video::new(
self.decoder.format(),
self.video_details.width as u32,
self.video_details.height as u32,
);
packet.set_pts(Some(frame_index as i64));
packet.set_dts(Some(frame_index as i64));
if !self.end_of_stream {
let _ = self.decoder.send_packet(&packet);
}
if self.decoder.receive_frame(&mut decoded).is_ok() {
let f = self.decode_frame(&decoded);
return Ok(f);
} else if self.end_of_stream {
return Err(DecoderError::EndOfFile);
}
}
}
}
}