VideoEncoder first pass, round trip test (#866)

Co-authored-by: Daniel Flores <danielflores3@fb.com>

Author: Dan-Flores

src/torchcodec/_core/Encoder.cpp

@@ -511,4 +511,283 @@ void AudioEncoder::flushBuffers() {
 
   encodeFrame(autoAVPacket, UniqueAVFrame(nullptr));
 }
+
+namespace {
+
+torch::Tensor validateFrames(const torch::Tensor& frames) {
+  TORCH_CHECK(
+      frames.dtype() == torch::kUInt8,
+      "frames must have uint8 dtype, got ",
+      frames.dtype());
+  TORCH_CHECK(
+      frames.dim() == 4,
+      "frames must have 4 dimensions (N, C, H, W), got ",
+      frames.dim());
+  TORCH_CHECK(
+      frames.sizes()[1] == 3,
+      "frame must have 3 channels (R, G, B), got ",
+      frames.sizes()[1]);
+  // TODO-VideoEncoder: Investigate if non-contiguous frames can be accepted
+  return frames.contiguous();
+}
+
+} // namespace
+
+VideoEncoder::~VideoEncoder() {
+  if (avFormatContext_ && avFormatContext_->pb) {
+    avio_flush(avFormatContext_->pb);
+    avio_close(avFormatContext_->pb);
+    avFormatContext_->pb = nullptr;
+  }
+}
+
+VideoEncoder::VideoEncoder(
+    const torch::Tensor& frames,
+    int frameRate,
+    std::string_view fileName,
+    const VideoStreamOptions& videoStreamOptions)
+    : frames_(validateFrames(frames)), inFrameRate_(frameRate) {
+  setFFmpegLogLevel();
+
+  // Allocate output format context
+  AVFormatContext* avFormatContext = nullptr;
+  int status = avformat_alloc_output_context2(
+      &avFormatContext, nullptr, nullptr, fileName.data());
+
+  TORCH_CHECK(
+      avFormatContext != nullptr,
+      "Couldn't allocate AVFormatContext. ",
+      "The destination file is ",
+      fileName,
+      ", check the desired extension? ",
+      getFFMPEGErrorStringFromErrorCode(status));
+  avFormatContext_.reset(avFormatContext);
+
+  status = avio_open(&avFormatContext_->pb, fileName.data(), AVIO_FLAG_WRITE);
+  TORCH_CHECK(
+      status >= 0,
+      "avio_open failed. The destination file is ",
+      fileName,
+      ", make sure it's a valid path? ",
+      getFFMPEGErrorStringFromErrorCode(status));
+  // TODO-VideoEncoder: Add tests for above fileName related checks
+
+  initializeEncoder(videoStreamOptions);
+}
+
+void VideoEncoder::initializeEncoder(
+    const VideoStreamOptions& videoStreamOptions) {
+  const AVCodec* avCodec =
+      avcodec_find_encoder(avFormatContext_->oformat->video_codec);
+  TORCH_CHECK(avCodec != nullptr, "Video codec not found");
+
+  AVCodecContext* avCodecContext = avcodec_alloc_context3(avCodec);
+  TORCH_CHECK(avCodecContext != nullptr, "Couldn't allocate codec context.");
+  avCodecContext_.reset(avCodecContext);
+
+  // Set encoding options
+  // TODO-VideoEncoder: Allow bitrate to be set
+  std::optional<int> desiredBitRate = videoStreamOptions.bitRate;
+  if (desiredBitRate.has_value()) {
+    TORCH_CHECK(
+        *desiredBitRate >= 0, "bit_rate=", *desiredBitRate, " must be >= 0.");
+  }
+  avCodecContext_->bit_rate = desiredBitRate.value_or(0);
+
+  // Store dimension order and input pixel format
+  // TODO-VideoEncoder: Remove assumption that tensor in NCHW format
+  auto sizes = frames_.sizes();
+  inPixelFormat_ = AV_PIX_FMT_GBRP;
+  inHeight_ = sizes[2];
+  inWidth_ = sizes[3];
+
+  // Use specified dimensions or input dimensions
+  // TODO-VideoEncoder: Allow height and width to be set
+  outWidth_ = videoStreamOptions.width.value_or(inWidth_);
+  outHeight_ = videoStreamOptions.height.value_or(inHeight_);
+
+  // Use YUV420P as default output format
+  // TODO-VideoEncoder: Enable other pixel formats
+  outPixelFormat_ = AV_PIX_FMT_YUV420P;
+
+  // Configure codec parameters
+  avCodecContext_->codec_id = avCodec->id;
+  avCodecContext_->width = outWidth_;
+  avCodecContext_->height = outHeight_;
+  avCodecContext_->pix_fmt = outPixelFormat_;
+  // TODO-VideoEncoder: Verify that frame_rate and time_base are correct
+  avCodecContext_->time_base = {1, inFrameRate_};
+  avCodecContext_->framerate = {inFrameRate_, 1};
+
+  // TODO-VideoEncoder: Allow GOP size and max B-frames to be set
+  if (videoStreamOptions.gopSize.has_value()) {
+    avCodecContext_->gop_size = *videoStreamOptions.gopSize;
+  } else {
+    avCodecContext_->gop_size = 12; // Default GOP size
+  }
+
+  if (videoStreamOptions.maxBFrames.has_value()) {
+    avCodecContext_->max_b_frames = *videoStreamOptions.maxBFrames;
+  } else {
+    avCodecContext_->max_b_frames = 0; // No max B-frames to reduce compression
+  }
+
+  int status = avcodec_open2(avCodecContext_.get(), avCodec, nullptr);
+  TORCH_CHECK(
+      status == AVSUCCESS,
+      "avcodec_open2 failed: ",
+      getFFMPEGErrorStringFromErrorCode(status));
+
+  AVStream* avStream = avformat_new_stream(avFormatContext_.get(), nullptr);
+  TORCH_CHECK(avStream != nullptr, "Couldn't create new stream.");
+
+  // Set the stream time base to encode correct frame timestamps
+  avStream->time_base = avCodecContext_->time_base;
+  status = avcodec_parameters_from_context(
+      avStream->codecpar, avCodecContext_.get());
+  TORCH_CHECK(
+      status == AVSUCCESS,
+      "avcodec_parameters_from_context failed: ",
+      getFFMPEGErrorStringFromErrorCode(status));
+  streamIndex_ = avStream->index;
+}
+
+void VideoEncoder::encode() {
+  // To be on the safe side we enforce that encode() can only be called once
+  TORCH_CHECK(!encodeWasCalled_, "Cannot call encode() twice.");
+  encodeWasCalled_ = true;
+
+  int status = avformat_write_header(avFormatContext_.get(), nullptr);
+  TORCH_CHECK(
+      status == AVSUCCESS,
+      "Error in avformat_write_header: ",
+      getFFMPEGErrorStringFromErrorCode(status));
+
+  AutoAVPacket autoAVPacket;
+  int numFrames = frames_.sizes()[0];
+  for (int i = 0; i < numFrames; ++i) {
+    torch::Tensor currFrame = frames_[i];
+    UniqueAVFrame avFrame = convertTensorToAVFrame(currFrame, i);
+    encodeFrame(autoAVPacket, avFrame);
+  }
+
+  flushBuffers();
+
+  status = av_write_trailer(avFormatContext_.get());
+  TORCH_CHECK(
+      status == AVSUCCESS,
+      "Error in av_write_trailer: ",
+      getFFMPEGErrorStringFromErrorCode(status));
+}
+
+UniqueAVFrame VideoEncoder::convertTensorToAVFrame(
+    const torch::Tensor& frame,
+    int frameIndex) {
+  // Initialize and cache scaling context if it does not exist
+  if (!swsContext_) {
+    swsContext_.reset(sws_getContext(
+        inWidth_,
+        inHeight_,
+        inPixelFormat_,
+        outWidth_,
+        outHeight_,
+        outPixelFormat_,
+        SWS_BILINEAR,
+        nullptr,
+        nullptr,
+        nullptr));
+    TORCH_CHECK(swsContext_ != nullptr, "Failed to create scaling context");
+  }
+
+  UniqueAVFrame avFrame(av_frame_alloc());
+  TORCH_CHECK(avFrame != nullptr, "Failed to allocate AVFrame");
+
+  // Set output frame properties
+  avFrame->format = outPixelFormat_;
+  avFrame->width = outWidth_;
+  avFrame->height = outHeight_;
+  avFrame->pts = frameIndex;
+
+  int status = av_frame_get_buffer(avFrame.get(), 0);
+  TORCH_CHECK(status >= 0, "Failed to allocate frame buffer");
+
+  // Need to convert/scale the frame
+  // Create temporary frame with input format
+  UniqueAVFrame inputFrame(av_frame_alloc());
+  TORCH_CHECK(inputFrame != nullptr, "Failed to allocate input AVFrame");
+
+  inputFrame->format = inPixelFormat_;
+  inputFrame->width = inWidth_;
+  inputFrame->height = inHeight_;
+
+  uint8_t* tensorData = static_cast<uint8_t*>(frame.data_ptr());
+
+  // TODO-VideoEncoder: Reorder tensor if in NHWC format
+  int channelSize = inHeight_ * inWidth_;
+  // Reorder RGB -> GBR for AV_PIX_FMT_GBRP format
+  // TODO-VideoEncoder: Determine if FFmpeg supports planar RGB input format
+  inputFrame->data[0] = tensorData + channelSize;
+  inputFrame->data[1] = tensorData + (2 * channelSize);
+  inputFrame->data[2] = tensorData;
+
+  inputFrame->linesize[0] = inWidth_;
+  inputFrame->linesize[1] = inWidth_;
+  inputFrame->linesize[2] = inWidth_;
+
+  status = sws_scale(
+      swsContext_.get(),
+      inputFrame->data,
+      inputFrame->linesize,
+      0,
+      inputFrame->height,
+      avFrame->data,
+      avFrame->linesize);
+  TORCH_CHECK(status == outHeight_, "sws_scale failed");
+  return avFrame;
+}
+
+void VideoEncoder::encodeFrame(
+    AutoAVPacket& autoAVPacket,
+    const UniqueAVFrame& avFrame) {
+  auto status = avcodec_send_frame(avCodecContext_.get(), avFrame.get());
+  TORCH_CHECK(
+      status == AVSUCCESS,
+      "Error while sending frame: ",
+      getFFMPEGErrorStringFromErrorCode(status));
+
+  while (true) {
+    ReferenceAVPacket packet(autoAVPacket);
+    status = avcodec_receive_packet(avCodecContext_.get(), packet.get());
+    if (status == AVERROR(EAGAIN) || status == AVERROR_EOF) {
+      if (status == AVERROR_EOF) {
+        // Flush remaining buffered packets
+        status = av_interleaved_write_frame(avFormatContext_.get(), nullptr);
+        TORCH_CHECK(
+            status == AVSUCCESS,
+            "Failed to flush packet: ",
+            getFFMPEGErrorStringFromErrorCode(status));
+      }
+      return;
+    }
+    TORCH_CHECK(
+        status >= 0,
+        "Error receiving packet: ",
+        getFFMPEGErrorStringFromErrorCode(status));
+
+    packet->stream_index = streamIndex_;
+
+    status = av_interleaved_write_frame(avFormatContext_.get(), packet.get());
+    TORCH_CHECK(
+        status == AVSUCCESS,
+        "Error in av_interleaved_write_frame: ",
+        getFFMPEGErrorStringFromErrorCode(status));
+  }
+}
+
+void VideoEncoder::flushBuffers() {
+  AutoAVPacket autoAVPacket;
+  // Send null frame to signal end of input
+  encodeFrame(autoAVPacket, UniqueAVFrame(nullptr));
+}
+
 } // namespace facebook::torchcodec

src/torchcodec/_core/Encoder.h

@@ -57,7 +57,6 @@ class AudioEncoder {
   bool encodeWasCalled_ = false;
   int64_t lastEncodedAVFramePts_ = 0;
 };
-} // namespace facebook::torchcodec
 
 /* clang-format off */
 //
@@ -121,3 +120,44 @@ class AudioEncoder {
 //
 //
 /* clang-format on */
+
+class VideoEncoder {
+ public:
+  ~VideoEncoder();
+
+  VideoEncoder(
+      const torch::Tensor& frames,
+      int frameRate,
+      std::string_view fileName,
+      const VideoStreamOptions& videoStreamOptions);
+
+  void encode();
+
+ private:
+  void initializeEncoder(const VideoStreamOptions& videoStreamOptions);
+  UniqueAVFrame convertTensorToAVFrame(
+      const torch::Tensor& frame,
+      int frameIndex);
+  void encodeFrame(AutoAVPacket& autoAVPacket, const UniqueAVFrame& avFrame);
+  void flushBuffers();
+
+  UniqueEncodingAVFormatContext avFormatContext_;
+  UniqueAVCodecContext avCodecContext_;
+  int streamIndex_;
+  UniqueSwsContext swsContext_;
+
+  const torch::Tensor frames_;
+  int inFrameRate_;
+
+  int inWidth_ = -1;
+  int inHeight_ = -1;
+  AVPixelFormat inPixelFormat_ = AV_PIX_FMT_NONE;
+
+  int outWidth_ = -1;
+  int outHeight_ = -1;
+  AVPixelFormat outPixelFormat_ = AV_PIX_FMT_NONE;
+
+  bool encodeWasCalled_ = false;
+};
+
+} // namespace facebook::torchcodec

src/torchcodec/_core/StreamOptions.h

@@ -38,6 +38,11 @@ struct VideoStreamOptions {
   std::optional<ColorConversionLibrary> colorConversionLibrary;
   // By default we use CPU for decoding for both C++ and python users.
   torch::Device device = torch::kCPU;
+
+  // Encoding options
+  std::optional<int> bitRate;
+  std::optional<int> gopSize;
+  std::optional<int> maxBFrames;
 };
 
 struct AudioStreamOptions {

src/torchcodec/_core/__init__.py

@@ -25,6 +25,7 @@
     encode_audio_to_file,
     encode_audio_to_file_like,
     encode_audio_to_tensor,
+    encode_video_to_file,
     get_ffmpeg_library_versions,
     get_frame_at_index,
     get_frame_at_pts,

src/torchcodec/_core/custom_ops.cpp

@@ -31,6 +31,8 @@ TORCH_LIBRARY(torchcodec_ns, m) {
   m.def("create_from_file(str filename, str? seek_mode=None) -> Tensor");
   m.def(
       "encode_audio_to_file(Tensor samples, int sample_rate, str filename, int? bit_rate=None, int? num_channels=None, int? desired_sample_rate=None) -> ()");
+  m.def(
+      "encode_video_to_file(Tensor frames, int frame_rate, str filename) -> ()");
   m.def(
       "encode_audio_to_tensor(Tensor samples, int sample_rate, str format, int? bit_rate=None, int? num_channels=None, int? desired_sample_rate=None) -> Tensor");
   m.def(
@@ -397,6 +399,19 @@ OpsAudioFramesOutput get_frames_by_pts_in_range_audio(
   return makeOpsAudioFramesOutput(result);
 }
 
+void encode_video_to_file(
+    const at::Tensor& frames,
+    int64_t frame_rate,
+    std::string_view file_name) {
+  VideoStreamOptions videoStreamOptions;
+  VideoEncoder(
+      frames,
+      validateInt64ToInt(frame_rate, "frame_rate"),
+      file_name,
+      videoStreamOptions)
+      .encode();
+}
+
 void encode_audio_to_file(
     const at::Tensor& samples,
     int64_t sample_rate,
@@ -701,6 +716,7 @@ TORCH_LIBRARY_IMPL(torchcodec_ns, BackendSelect, m) {
 
 TORCH_LIBRARY_IMPL(torchcodec_ns, CPU, m) {
   m.impl("encode_audio_to_file", &encode_audio_to_file);
+  m.impl("encode_video_to_file", &encode_video_to_file);
   m.impl("encode_audio_to_tensor", &encode_audio_to_tensor);
   m.impl("seek_to_pts", &seek_to_pts);
   m.impl("add_video_stream", &add_video_stream);