Disambiguate audio sample stride

Summary:
"Audio sample stride" has be used to designate the audio sample frame stride, meaning the stride of the group of audio samples captured synchronously, not the padded size of a single audio channel sample.
This diff changes the name of the constant and better documents what it means, without breaking compatibility with existing files, as the label saved in vrs files reamains unchanged.

Reviewed By: perdoch

Differential Revision: D64868230

fbshipit-source-id: 9ae1e85ccd1375f0812808cfcae84dfcd4bad2b9

vrs/DataLayoutConventions.h

@@ -112,8 +112,9 @@ class VideoFrameSpec : public AutoDataLayout {
 constexpr const char* kAudioFormat = "audio_format";
 /// DataLayout convention name for the audio sample format (see vrs::AudioSampleFormat).
 constexpr const char* kAudioSampleFormat = "audio_sample_format";
-/// DataLayout convention name for the padded number of bytes per sample.
-constexpr const char* kAudioSampleStride = "audio_sample_stride";
+/// DataLayout convention name for the padded number of bytes per sample frame.
+/// A sample frame is made of kAudioChannelCount synchronous audio channel samples.
+constexpr const char* kAudioSampleFrameStride = "audio_sample_stride";
 /// DataLayout convention name for the audio channel count: mono = 1, stereo = 2, etc.
 constexpr const char* kAudioChannelCount = "audio_channel_count";
 /// DataLayout convention name for the sample rate (samples per seconde).
@@ -137,7 +138,7 @@ class AudioSpec : public AutoDataLayout {
  public:
   DataPieceEnum<AudioFormat, uint8_t> audioFormat{kAudioFormat}; ///< optional
   DataPieceEnum<AudioSampleFormat, uint8_t> sampleType{kAudioSampleFormat};
-  DataPieceValue<uint8_t> sampleStride{kAudioSampleStride};
+  DataPieceValue<uint8_t> sampleStride{kAudioSampleFrameStride};
   DataPieceValue<uint8_t> channelCount{kAudioChannelCount};
   DataPieceValue<uint32_t> sampleRate{kAudioSampleRate};
   DataPieceValue<uint32_t> sampleCount{kAudioSampleCount};