Merge branch 'migrate_encoding_test' into encoding_sample_rate_lezzzgo

Author: NicolasHug

src/torchcodec/_core/Encoder.cpp

@@ -183,6 +183,8 @@ void AudioEncoder::initializeEncoder(
 
   numChannelsOutput_ = static_cast<int>(numChannels.value_or(wf_.sizes()[0]));
   validateNumChannels(*avCodec, numChannelsOutput_);
+  // The avCodecContext layout defines the layout of the encoded output, it's
+  // not related to the input sampes.
   setDefaultChannelLayout(avCodecContext_, numChannelsOutput_);
 
   sampleRateOutput_ =
@@ -239,6 +241,8 @@ void AudioEncoder::encode() {
   avFrame->format = AV_SAMPLE_FMT_FLTP;
   avFrame->sample_rate = sampleRateInput_;
   avFrame->pts = 0;
+  // We set the channel layout of the frame to the default layout corresponding
+  // to the input samples' number of channels
   setDefaultChannelLayout(avFrame, static_cast<int>(wf_.sizes()[0]));
 
   auto status = av_frame_get_buffer(avFrame.get(), 0);

src/torchcodec/_core/FFMPEGCommon.cpp

@@ -107,15 +107,17 @@ void validateNumChannels(const AVCodec& avCodec, int numChannels) {
     // eventually raise.
     return;
   }
-  for (auto i = 0; avCodec.ch_layouts[i].order != AV_CHANNEL_ORDER_UNSPEC;
-       ++i) {
+  // FFmpeg doc indicate that the ch_layouts array is terminated by a zeroed
+  // layout, so checking for nb_channels == 0 should indicate its end.
+  for (auto i = 0; avCodec.ch_layouts[i].nb_channels != 0; ++i) {
     if (numChannels == avCodec.ch_layouts[i].nb_channels) {
       return;
     }
   }
+  // At this point it seems that the encoder doesn't support the requested
+  // number of channels, so we error out.
   std::stringstream supportedNumChannels;
-  for (auto i = 0; avCodec.ch_layouts[i].order != AV_CHANNEL_ORDER_UNSPEC;
-       ++i) {
+  for (auto i = 0; avCodec.ch_layouts[i].nb_channels != 0; ++i) {
     if (i > 0) {
       supportedNumChannels << ", ";
     }
@@ -132,6 +134,8 @@ void validateNumChannels(const AVCodec& avCodec, int numChannels) {
       return;
     }
   }
+  // At this point it seems that the encoder doesn't support the requested
+  // number of channels, so we error out.
   std::stringstream supportedNumChannels;
   for (auto i = 0; avCodec.channel_layouts[i] != 0; ++i) {
     if (i > 0) {