atranscoder-rpc/src/transcoder.rs

extern crate ffmpeg_next as ffmpeg;

use std::error::Error;
use std::sync::Arc;

use ffmpeg::{codec, filter, format, frame, media};

pub struct Transcoder {
    params: Arc<TranscoderParams>,
    pub(crate) stream: usize,
    filter: filter::Graph,
    decoder: codec::decoder::Audio,
    encoder: codec::encoder::Audio,
    pub(crate) in_time_base: ffmpeg::Rational,
    out_time_base: ffmpeg::Rational,
}

pub struct TranscoderParams {
    pub codec: String,
    pub bit_rate: usize,
    pub max_bit_rate: usize,
    pub sample_rate: i32,
    pub channel_layout: ffmpeg::channel_layout::ChannelLayout,
}

impl Transcoder {
    pub fn new(
        ictx: &mut format::context::Input,
        octx: &mut format::context::Output,
        params: TranscoderParams,
    ) -> Result<Transcoder, ffmpeg::Error> {
        let input = ictx
            .streams()
            .best(media::Type::Audio)
            .expect("could not find best audio stream");
        let context = codec::context::Context::from_parameters(input.parameters())?;
        let mut decoder = context.decoder().audio()?;
        let codec = ffmpeg::encoder::find_by_name(&*params.codec)
            .expect(format!("failed to find encoder with name: {}", params.codec).as_str())
            .audio()?;
        let global = octx
            .format()
            .flags()
            .contains(format::flag::Flags::GLOBAL_HEADER);

        decoder.set_parameters(input.parameters())?;

        let mut output = octx.add_stream(codec)?;
        let context = codec::context::Context::from_parameters(output.parameters())?;
        let mut encoder = context.encoder().audio()?;

        if global {
            encoder.set_flags(codec::flag::Flags::GLOBAL_HEADER);
        }

        let sample_rate = if params.sample_rate > 0 {
            params.sample_rate
        } else {
            decoder.rate() as i32
        };

        encoder.set_rate(sample_rate);
        encoder.set_channel_layout(params.channel_layout);
        #[cfg(not(feature = "ffmpeg_7_0"))]
        {
            encoder.set_channels(params.channel_layout.channels());
        }
        encoder.set_format(
            codec
                .formats()
                .expect(format!("failed to get supported formats for codec: {}", codec.name()).as_str())
                .next()
                .unwrap(),
        );

        if params.bit_rate > 0 {
            encoder.set_bit_rate(params.bit_rate);
        } else {
            encoder.set_bit_rate(decoder.bit_rate());
        }

        if params.max_bit_rate > 0 {
            encoder.set_max_bit_rate(params.bit_rate);
        } else {
            encoder.set_max_bit_rate(decoder.max_bit_rate());
        }

        encoder.set_time_base((1, sample_rate));
        output.set_time_base((1, sample_rate));

        let encoder = encoder.open_as(codec)?;
        output.set_parameters(&encoder);

        let filter = filter("anull", &decoder, &encoder)?;

        let in_time_base = decoder.time_base();
        let out_time_base = output.time_base();

        Ok(Transcoder {
            stream: input.index(),
            params: Arc::new(params),
            filter,
            decoder,
            encoder,
            in_time_base,
            out_time_base,
        })
    }

    fn send_frame_to_encoder(&mut self, frame: &ffmpeg::Frame) -> Result<(), ffmpeg::Error> {
        self.encoder.send_frame(frame)
    }

    pub(crate) fn send_eof_to_encoder(&mut self) {
        self.encoder.send_eof().unwrap();
    }

    pub(crate) fn receive_and_process_encoded_packets(&mut self, octx: &mut format::context::Output) {
        let mut encoded = ffmpeg::Packet::empty();
        while self.encoder.receive_packet(&mut encoded).is_ok() {
            encoded.set_stream(0);
            encoded.rescale_ts(self.in_time_base, self.out_time_base);
            encoded.write_interleaved(octx).unwrap();
        }
    }

    fn add_frame_to_filter(&mut self, frame: &ffmpeg::Frame) {
        self.filter.get("in").unwrap().source().add(frame).unwrap();
    }

    pub(crate) fn flush_filter(&mut self) {
        self.filter.get("in").unwrap().source().flush().unwrap();
    }

    pub(crate) fn get_and_process_filtered_frames(&mut self, octx: &mut format::context::Output) {
        let mut filtered = frame::Audio::empty();
        while self
            .filter
            .get("out")
            .unwrap()
            .sink()
            .frame(&mut filtered)
            .is_ok()
        {
            self.send_frame_to_encoder(&filtered);
            self.receive_and_process_encoded_packets(octx);
        }
    }

    pub(crate) fn send_packet_to_decoder(&mut self, packet: &ffmpeg::Packet) {
        self.decoder.send_packet(packet).unwrap();
    }

    pub(crate) fn send_eof_to_decoder(&mut self) {
        self.decoder.send_eof().unwrap();
    }

    pub(crate) fn receive_and_process_decoded_frames(&mut self, octx: &mut format::context::Output) {
        let mut decoded = frame::Audio::empty();
        while self.decoder.receive_frame(&mut decoded).is_ok() {
            let timestamp = decoded.timestamp();
            decoded.set_pts(timestamp);
            self.add_frame_to_filter(&decoded);
            self.get_and_process_filtered_frames(octx);
        }
    }
}

fn filter(
    spec: &str,
    decoder: &codec::decoder::Audio,
    encoder: &codec::encoder::Audio,
) -> Result<filter::Graph, ffmpeg::Error> {
    let mut filter = filter::Graph::new();

    let args = format!(
        "time_base={}:sample_rate={}:sample_fmt={}:channel_layout=0x{:x}",
        decoder.time_base(),
        decoder.rate(),
        decoder.format().name(),
        decoder.channel_layout().bits()
    );

    filter.add(&filter::find("abuffer").unwrap(), "in", &args)?;
    filter.add(&filter::find("abuffersink").unwrap(), "out", "")?;

    {
        let mut out = filter.get("out").unwrap();

        out.set_sample_format(encoder.format());
        out.set_channel_layout(encoder.channel_layout());
        out.set_sample_rate(encoder.rate());
    }

    filter.output("in", 0)?.input("out", 0)?.parse(spec)?;
    filter.validate()?;

    println!("{}", filter.dump());

    if let Some(codec) = encoder.codec() {
        if !codec
            .capabilities()
            .contains(codec::capabilities::Capabilities::VARIABLE_FRAME_SIZE)
        {
            filter
                .get("out")
                .unwrap()
                .sink()
                .set_frame_size(encoder.frame_size());
        }
    }

    Ok(filter)
}