FFMPEG Core - Video Decoding Modification

I changed the way video decoding works slightly in the FFMPEG
core to, hopefully, enable CODECs that don't play well--such
as AV1 in my experience--with the current strategy.

The changes I've made have been done to more precisely follow
the recommendations of the FFMPEG developers with respect to
swapping between sending packets and receiving frames.

Author: kaysedwards

cores/libretro-ffmpeg/ffmpeg_core.c

@@ -1570,11 +1570,12 @@ static void sws_worker_thread(void *arg)
 }
 
 #ifdef HAVE_SSA
-static void decode_video(AVCodecContext *ctx, AVPacket *pkt, size_t frame_size, ASS_Track *ass_track_active)
+static int decode_video(AVCodecContext *ctx, AVPacket *pkt, size_t frame_size, ASS_Track *ass_track_active)
 #else
-static void decode_video(AVCodecContext *ctx, AVPacket *pkt, size_t frame_size)
+static int decode_video(AVCodecContext *ctx, AVPacket *pkt, size_t frame_size)
 #endif
 {
+   static bool receiving = false;
    int ret = 0;
    video_decoder_context_t *decoder_ctx = NULL;
 
@@ -1584,72 +1585,83 @@ static void decode_video(AVCodecContext *ctx, AVPacket *pkt, size_t frame_size)
       if (main_sleeping)
       {
          if (!do_seek)
+         {
             log_cb(RETRO_LOG_ERROR, "[FFMPEG] Thread: Video deadlock detected.\n");
+            return -1;
+         }
          tpool_wait(tpool);
          video_buffer_clear(video_buffer);
-         return;
+         return 1;
       }
    }
 
-   if ((ret = avcodec_send_packet(ctx, pkt)) < 0)
-   {
-#ifdef __cplusplus
-      log_cb(RETRO_LOG_ERROR, "[FFMPEG] Can't decode video packet: %d\n", ret);
-#else
-      log_cb(RETRO_LOG_ERROR, "[FFMPEG] Can't decode video packet: %s\n", av_err2str(ret));
-#endif
-      return;
-   }
-
-   while (!decode_thread_dead && video_buffer_has_open_slot(video_buffer))
+   if (!receiving)
    {
-      video_buffer_get_open_slot(video_buffer, &decoder_ctx);
+      ret = avcodec_send_packet(ctx, pkt);
 
-      ret = avcodec_receive_frame(ctx, decoder_ctx->source);
-      if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
+      if (ret == AVERROR(EAGAIN) || ret >= 0)
       {
-         ret = -42;
-         goto end;
+         receiving = true;
+         return 1;
       }
       else if (ret < 0)
       {
 #ifdef __cplusplus
-         log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error while reading video frame: %d\n", ret);
+         log_cb(RETRO_LOG_ERROR, "[FFMPEG] Can't decode video packet: %d\n", ret);
 #else
-         log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error while reading video frame: %s\n", av_err2str(ret));
+         log_cb(RETRO_LOG_ERROR, "[FFMPEG] Can't decode video packet: %s\n", av_err2str(ret));
 #endif
-         goto end;
+         return -1;
       }
+   }
+   else
+   {
+      if (video_buffer_has_open_slot(video_buffer))
+      {
+         video_buffer_get_open_slot(video_buffer, &decoder_ctx);
 
-#if ENABLE_HW_ACCEL
-      if (hw_decoding_enabled)
-         /* Copy data from VRAM to RAM */
-         if ((ret = av_hwframe_transfer_data(decoder_ctx->hw_source, decoder_ctx->source, 0)) < 0)
+         ret = avcodec_receive_frame(ctx, decoder_ctx->source);
+
+         if (ret >= 0)
+         {
+#ifdef HAVE_SSA
+            decoder_ctx->ass_track_active = ass_track_active;
+#endif
+            tpool_add_work(tpool, sws_worker_thread, decoder_ctx);
+            return 1;
+         }
+         else if (ret == AVERROR(EAGAIN))
          {
+#if ENABLE_HW_ACCEL
+            if (hw_decoding_enabled)
+               /* Copy data from VRAM to RAM */
+               if ((ret = av_hwframe_transfer_data(decoder_ctx->hw_source, decoder_ctx->source, 0)) < 0)
+               {
 #ifdef __cplusplus
-               log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error transferring the data to system memory: %d\n", ret);
+                  log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error transferring the data to system memory: %d\n", ret);
 #else
-               log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error transferring the data to system memory: %s\n", av_err2str(ret));
+                  log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error transferring the data to system memory: %s\n", av_err2str(ret));
 #endif
-               goto end;
-         }
+               }
 #endif
 
-#ifdef HAVE_SSA
-      decoder_ctx->ass_track_active = ass_track_active;
+            video_buffer_return_open_slot(video_buffer, decoder_ctx);
+            receiving = false;
+            return 0;
+         }
+         else if (ret < 0)
+         {
+#ifdef __cplusplus
+            log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error while reading video frame: %d\n", ret);
+#else
+            log_cb(RETRO_LOG_ERROR, "[FFMPEG] Error while reading video frame: %s\n", av_err2str(ret));
 #endif
-
-      tpool_add_work(tpool, sws_worker_thread, decoder_ctx);
-
-   end:
-      if (ret < 0)
-      {
-         video_buffer_return_open_slot(video_buffer, decoder_ctx);
-         break;
+            return -1;
+         }
       }
    }
 
-   return;
+   return 0;
 }
 
 static int16_t *decode_audio(AVCodecContext *ctx, AVPacket *pkt,
@@ -1922,9 +1934,9 @@ static void decode_thread(void *data)
          packet_buffer_get_packet(video_packet_buffer, pkt);
 
          #ifdef HAVE_SSA
-         decode_video(vctx, pkt, frame_size, ass_track_active);
+         while(decode_video(vctx, pkt, frame_size, ass_track_active) > 0);
          #else
-         decode_video(vctx, pkt, frame_size);
+         while(decode_video(vctx, pkt, frame_size) > 0);
          #endif
 
          av_packet_unref(pkt);
@@ -2231,8 +2243,8 @@ bool CORE_PREFIX(retro_load_game)(const struct retro_game_info *info)
       { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_RIGHT, "Increment Subtitle Index" },
       { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_UP,    "Increment Audio Index" },
       { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_DOWN,  "Decrement Audio Index" },
-      { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_L,     "Seek -60 seconds" },
-      { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_R,     "Seek +60 seconds" },
+      { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_L,     "Seek -30 seconds" },
+      { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_R,     "Seek +30 seconds" },
       { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_L2,     "Seek Decrementally" },
       { 0, RETRO_DEVICE_JOYPAD, 0, RETRO_DEVICE_ID_JOYPAD_R2,     "Seek Incrementally" },