Fix loop to make it exactly like torchaudio

Author: NicolasHug

src/torchcodec/decoders/_core/VideoDecoder.cpp

@@ -1063,12 +1063,18 @@ VideoDecoder::AVFrameStream VideoDecoder::decodeAVFrame(
   int ffmpegStatus = AVSUCCESS;
   bool reachedEOF = false;
   while (true) {
+    if (veryFirstCall_) {
+      veryFirstCall_ = false;
+      goto av_read_frame_call;
+    }
+  begin_loop:
     ffmpegStatus =
         avcodec_receive_frame(streamInfo.codecContext.get(), avFrame.get());
-    // printf("output of avcodec_receive_frame: %d\n", ffmpegStatus);
+    printf("output of avcodec_receive_frame: %d\n", ffmpegStatus);
 
     if (ffmpegStatus != AVSUCCESS && ffmpegStatus != AVERROR(EAGAIN)) {
       // Non-retriable error
+      printf("Non-retriable error\n");
       break;
     }
 
@@ -1078,55 +1084,65 @@ VideoDecoder::AVFrameStream VideoDecoder::decodeAVFrame(
       // Yes, this is the frame we'll return; break out of the decoding loop.
       // printf("%ld %ld\n", avFrame->pts, avFrame->duration);
 
+      printf("Found frame\n");
       break;
     } else if (ffmpegStatus == AVSUCCESS) {
       // No, but we received a valid frame - just not the kind we're looking
       // for. The logic below will read packets and send them to the decoder.
       // But since we did just receive a frame, we should skip reading more
       // packets and sending them to the decoder and just try to receive more
       // frames from the decoder.
+      printf("Got AVSUCCESS, continue\n");
       continue;
     }
 
     if (reachedEOF) {
       // We don't have any more packets to send to the decoder. So keep on
       // pulling frames from its internal buffers.
+      printf("Reached EOF, continue\n");
       continue;
     }
 
-    // We still haven't found the frame we're looking for. So let's read more
-    // packets and send them to the decoder.
+  av_read_frame_call:
     ReferenceAVPacket packet(autoAVPacket);
-    ffmpegStatus = av_read_frame(formatContext_.get(), packet.get());
-    decodeStats_.numPacketsRead++;
+    while (true) {
+      // We still haven't found the frame we're looking for. So let's read more
+      // packets and send them to the decoder.
+      ffmpegStatus = av_read_frame(formatContext_.get(), packet.get());
+      decodeStats_.numPacketsRead++;
+
+      if (ffmpegStatus == AVERROR_EOF) {
+        // End of file reached. We must drain the codec by sending a nullptr
+        // packet.
+        ffmpegStatus = avcodec_send_packet(
+            streamInfo.codecContext.get(),
+            /*avpkt=*/nullptr);
+        if (ffmpegStatus < AVSUCCESS) {
+          throw std::runtime_error(
+              "Could not flush decoder: " +
+              getFFMPEGErrorStringFromErrorCode(ffmpegStatus));
+        }
+
+        // We've reached the end of file so we can't read any more packets from
+        // it, but the decoder may still have frames to read in its buffer.
+        // Continue iterating to try reading frames.
+        reachedEOF = true;
+        goto begin_loop;
+        //   continue;
+      }
 
-    if (ffmpegStatus == AVERROR_EOF) {
-      // End of file reached. We must drain the codec by sending a nullptr
-      // packet.
-      ffmpegStatus = avcodec_send_packet(
-          streamInfo.codecContext.get(),
-          /*avpkt=*/nullptr);
       if (ffmpegStatus < AVSUCCESS) {
         throw std::runtime_error(
-            "Could not flush decoder: " +
+            "Could not read frame from input file: " +
             getFFMPEGErrorStringFromErrorCode(ffmpegStatus));
       }
 
-      // We've reached the end of file so we can't read any more packets from
-      // it, but the decoder may still have frames to read in its buffer.
-      // Continue iterating to try reading frames.
-      reachedEOF = true;
-      continue;
-    }
-
-    if (ffmpegStatus < AVSUCCESS) {
-      throw std::runtime_error(
-          "Could not read frame from input file: " +
-          getFFMPEGErrorStringFromErrorCode(ffmpegStatus));
-    }
-
-    if (packet->stream_index != activeStreamIndex_) {
-      continue;
+      if (packet->stream_index == activeStreamIndex_) {
+        printf("found packet for stream\n");
+        break;
+      } else {
+        printf("Not for stream, continue\n");
+      }
     }
 
     // We got a valid packet. Send it to the decoder, and we'll receive it in

src/torchcodec/decoders/_core/VideoDecoder.h

@@ -477,6 +477,7 @@ class VideoDecoder {
   // ATTRIBUTES
   // --------------------------------------------------------------------------
 
+  bool veryFirstCall_ = true;
   SeekMode seekMode_;
   ContainerMetadata containerMetadata_;
   UniqueAVFormatContext formatContext_;