Explicitly set frames pts values

Author: NicolasHug

src/torchcodec/_core/Encoder.cpp

@@ -293,8 +293,7 @@ void AudioEncoder::encode() {
     encodeInnerLoop(autoAVPacket, convertedAVFrame);
 
     numEncodedSamples += numSamplesToEncode;
-    // TODO-ENCODING set frame pts correctly, and test against it.
-    // avFrame->pts += static_cast<int64_t>(numSamplesToEncode);
+    avFrame->pts += static_cast<int64_t>(numSamplesToEncode);
   }
   TORCH_CHECK(numEncodedSamples == numSamples, "Hmmmmmm something went wrong.");
 

src/torchcodec/_core/FFMPEGCommon.cpp

@@ -274,6 +274,7 @@ UniqueAVFrame convertAudioAVFrameSamples(
       convertedAVFrame,
       "Could not allocate frame for sample format conversion.");
 
+  convertedAVFrame->pts = srcAVFrame->pts;
   convertedAVFrame->format = static_cast<int>(outSampleFormat);
 
   convertedAVFrame->sample_rate = outSampleRate;