wip: transcoding

Cargo.toml

@@ -14,3 +14,4 @@ tracing = "0.1.37"
 tracing-subscriber = { version = "0.3.16", features = ["env-filter"] }
 tower-http = { version = "0.5.2", features = ["trace"] }
 num_cpus = "1.16.0"
+ffmpeg-next = "7.0.1"

Dockerfile

@@ -0,0 +1,2 @@
+FROM alpine:latest
+RUN apk add --no-cache ffmpeg-libavutil ffmpeg-libavformat ffmpeg-libavfilter ffmpeg-libavdevice clang16

src/dto.rs

@@ -19,6 +19,7 @@ pub struct ConvertRequest {
     pub codec: String,
     pub bit_rate: usize,
     pub max_bit_rate: usize,
+    pub sample_rate: i32,
     pub channel_layout: String,
     pub upload_url: String,
 

src/main.rs

@@ -9,6 +9,7 @@ mod dto;
 mod server;
 mod task;
 mod thread_pool;
+mod transcoder;
 
 #[tokio::main]
 async fn main() {

src/server.rs

@@ -1,7 +1,7 @@
 use std::path::Path;
 use std::sync::Arc;
 
-use axum::{debug_handler, Json, Router};
+use axum::{Json, Router};
 use axum::extract::{DefaultBodyLimit, State};
 use axum::http::StatusCode;
 use axum::routing::post;
@@ -81,6 +81,7 @@ async fn enqueue_file(
                 req.codec,
                 req.bit_rate,
                 req.max_bit_rate,
+                req.sample_rate,
                 req.channel_layout,
                 req.upload_url,
                 input_path.unwrap().to_string(),

src/task.rs

@@ -1,10 +1,14 @@
-use tracing::debug;
+use tracing::{debug, error};
+use ffmpeg_next::{Error, format};
+use ffmpeg_next::channel_layout::ChannelLayout;
+use crate::transcoder::{Transcoder, TranscoderParams};
 
 pub struct Task {
     id: uuid::Uuid,
     codec: String,
     bit_rate: usize,
     max_bit_rate: usize,
+    sample_rate: i32,
     channel_layout: String,
     input_path: String,
     output_path: String,
@@ -17,6 +21,7 @@ impl Task {
         codec: String,
         bit_rate: usize,
         max_bit_rate: usize,
+        sample_rate: i32,
         channel_layout: String,
         upload_url: String,
         input_path: String,
@@ -27,6 +32,7 @@ impl Task {
             codec,
             bit_rate,
             max_bit_rate,
+            sample_rate,
             channel_layout,
             input_path,
             output_path,
@@ -34,7 +40,51 @@ impl Task {
         }
     }
 
-    pub fn execute(&self) {
-        debug!("Executing task with id: {}", self.id.to_string());
+    pub fn execute(self) {
+        debug!("performing transcoding for task with id: {}", self.id.to_string());
+        let mut ictx = format::input(&self.input_path).unwrap();
+        let mut octx = format::output_as(&self.output_path, &self.codec).unwrap();
+        let transcoder = Transcoder::new(&mut ictx, &mut octx, TranscoderParams {
+            codec: self.codec,
+            bit_rate: self.bit_rate,
+            max_bit_rate: self.max_bit_rate,
+            sample_rate: self.sample_rate,
+            channel_layout: match self.channel_layout.as_str() {
+                "stereo" => ChannelLayout::STEREO,
+                "mono" => ChannelLayout::MONO,
+                "stereo_downmix" => ChannelLayout::STEREO_DOWNMIX,
+                _ => ChannelLayout::STEREO,
+            }
+        });
+        let mut transcoder = match transcoder {
+            Ok(val) => val,
+            Err(err) => {
+                error!("couldn't initialize FFmpeg transcoder: {:?}", err);
+                return
+            }
+        };
+        octx.set_metadata(ictx.metadata().to_owned());
+        octx.write_header()
+            .unwrap_or_else(|err| error!("couldn't start transcoding: {:?}", err));
+
+        for (stream, mut packet) in ictx.packets() {
+            if stream.index() == transcoder.stream {
+                packet.rescale_ts(stream.time_base(), transcoder.in_time_base);
+                transcoder.send_packet_to_decoder(&packet);
+                transcoder.receive_and_process_decoded_frames(&mut octx);
+            }
+        }
+
+        transcoder.send_eof_to_decoder();
+        transcoder.receive_and_process_decoded_frames(&mut octx);
+
+        transcoder.flush_filter();
+        transcoder.get_and_process_filtered_frames(&mut octx);
+
+        transcoder.send_eof_to_encoder();
+        transcoder.receive_and_process_encoded_packets(&mut octx);
+
+        octx.write_trailer()
+            .unwrap_or_else(|err| error!("couldn't finish transcoding: {:?}", err));
     }
 }

src/thread_pool.rs

@@ -39,20 +39,25 @@ struct Worker {
 
 impl Worker {
     fn new(id: usize, receiver: Arc<Mutex<Receiver<Task>>>) -> Self {
-        let thread = thread::spawn(move || loop {
-            let task = {
-                let lock = receiver.lock().unwrap();
-                lock.recv()
-            };
+        let thread = thread::spawn(move || {
+            ffmpeg_next::init()
+                .unwrap_or_else(|err| tracing::error!("couldn't init FFmpeg: {:?}", err));
 
-            match task {
-                Ok(task) => {
-                    debug!("worker {} got a task; executing.", id);
-                    task.execute();
-                }
-                Err(e) => {
-                    error!("worker {} failed to receive task: {:?}", id, e);
-                    thread::sleep(Duration::from_secs(1)); // sleep to avoid busy-looping
+            loop {
+                let task = {
+                    let lock = receiver.lock().unwrap();
+                    lock.recv()
+                };
+
+                match task {
+                    Ok(task) => {
+                        debug!("worker {} got a task; executing.", id);
+                        task.execute();
+                    }
+                    Err(e) => {
+                        error!("worker {} failed to receive task: {:?}", id, e);
+                        thread::sleep(Duration::from_secs(1)); // sleep to avoid busy-looping
+                    }
                 }
             }
         });

src/transcoder.rs

@@ -0,0 +1,214 @@
+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)
+}