Bug 1765480 - "send" before "receive"-ing when decoding audio using ffmpeg. r=alwu

This is what the documentation says we should be doing (and it's clearly the
right thing to do). We miss decoding a packet otherwise.

Depends on D150974

Differential Revision: https://phabricator.services.mozilla.com/D150975

dom/media/platforms/ffmpeg/FFmpegAudioDecoder.cpp

@@ -269,21 +269,7 @@ MediaResult FFmpegAudioDecoder<LIBAV_VER>::DoDecode(MediaRawData* aSample,
     }
 #else
 #  define AVRESULT_OK 0
-
-    int ret = mLib->avcodec_receive_frame(mCodecContext, mFrame);
-    switch (ret) {
-      case AVRESULT_OK:
-        decoded = true;
-        break;
-      case AVERROR(EAGAIN):
-        break;
-      case AVERROR_EOF: {
-        FFMPEG_LOG("  End of stream.");
-        return MediaResult(NS_ERROR_DOM_MEDIA_END_OF_STREAM,
-                           RESULT_DETAIL("End of stream"));
-      }
-    }
-    ret = mLib->avcodec_send_packet(mCodecContext, &packet);
+    int ret = mLib->avcodec_send_packet(mCodecContext, &packet);
     switch (ret) {
       case AVRESULT_OK:
         bytesConsumed = packet.size;
@@ -299,6 +285,20 @@ MediaResult FFmpegAudioDecoder<LIBAV_VER>::DoDecode(MediaRawData* aSample,
         return MediaResult(NS_ERROR_DOM_MEDIA_DECODE_ERR,
                            RESULT_DETAIL("FFmpeg audio error"));
     }
+
+    ret = mLib->avcodec_receive_frame(mCodecContext, mFrame);
+    switch (ret) {
+      case AVRESULT_OK:
+        decoded = true;
+        break;
+      case AVERROR(EAGAIN):
+        break;
+      case AVERROR_EOF: {
+        FFMPEG_LOG("  End of stream.");
+        return MediaResult(NS_ERROR_DOM_MEDIA_END_OF_STREAM,
+                           RESULT_DETAIL("End of stream"));
+      }
+    }
 #endif
 
     if (decoded) {