ffmpeg: Reset the flush packet after each keyframe.

This handles cases where the packet may contain a frame
that triggers a decoder reset - we do not want to cause
a reset during the flushing process.

ffmpeg/decoder.c

@@ -22,12 +22,12 @@ static int lpms_receive_frame(struct input_ctx *ictx, AVCodecContext *dec, AVFra
     return ret;
 }
 
-static int send_first_pkt(struct input_ctx *ictx)
+static int send_flush_pkt(struct input_ctx *ictx)
 {
   if (ictx->flushed) return 0;
-  if (!ictx->first_pkt) return lpms_ERR_INPUT_NOKF;
+  if (!ictx->flush_pkt) return lpms_ERR_INPUT_NOKF;
 
-  int ret = avcodec_send_packet(ictx->vc, ictx->first_pkt);
+  int ret = avcodec_send_packet(ictx->vc, ictx->flush_pkt);
   ictx->sentinel_count++;
   if (ret < 0) {
     LPMS_ERR(packet_cleanup, "Error sending flush packet");
@@ -68,9 +68,14 @@ int decode_in(struct input_ctx *ictx, AVPacket *pkt, AVFrame *frame, int *stream
     return 0;
   }
 
-  if (!ictx->first_pkt && pkt->flags & AV_PKT_FLAG_KEY && decoder == ictx->vc) {
-    ictx->first_pkt = av_packet_clone(pkt);
-    ictx->first_pkt->pts = -1;
+  // Set up flush packet. Do this every keyframe in case the underlying frame changes
+  if (pkt->flags & AV_PKT_FLAG_KEY && decoder == ictx->vc) {
+    if (!ictx->flush_pkt) ictx->flush_pkt = av_packet_clone(pkt);
+    else {
+      av_packet_unref(ictx->flush_pkt);
+      av_packet_ref(ictx->flush_pkt, pkt);
+    }
+    ictx->flush_pkt->pts = -1;
   }
 
   ret = lpms_send_packet(ictx, decoder, pkt);
@@ -104,7 +109,7 @@ int flush_in(struct input_ctx *ictx, AVFrame *frame, int *stream_index)
   // TODO this is unnecessary for SW decoding! SW process should match audio
   if (ictx->vc && !ictx->flushed && ictx->pkt_diff > 0) {
     ictx->flushing = 1;
-    ret = send_first_pkt(ictx);
+    ret = send_flush_pkt(ictx);
     if (ret < 0) {
       ictx->flushed = 1;
       return ret;

ffmpeg/decoder.h

@@ -20,7 +20,7 @@ struct input_ctx {
   char *xcoderParams;
 
   // Decoder flush
-  AVPacket *first_pkt;
+  AVPacket *flush_pkt;
   int flushed;
   int flushing;
   // The diff of `packets sent - frames recv` serves as an estimate of

ffmpeg/transcoder.c

@@ -43,7 +43,7 @@ const int lpms_ERR_UNRECOVERABLE = FFERRTAG('U', 'N', 'R', 'V');
 
 // MOVED TO decoder.[ch]
 //  Decoder: For audio, we pay the price of closing and re-opening the decoder.
-//           For video, we cache the first packet we read (input_ctx.first_pkt).
+//           For video, we cache the last keyframe read  (input_ctx.flush_pkt).
 //           The pts is set to a sentinel value and fed to the decoder. Once we
 //           receive all frames from the decoder OR have sent too many sentinel
 //           pkts without receiving anything, then we know the decoder has been
@@ -133,7 +133,7 @@ int transcode_shutdown(struct transcode_thread *h, int ret)
   ictx->flushing = 0;
   ictx->pkt_diff = 0;
   ictx->sentinel_count = 0;
-  if (ictx->first_pkt) av_packet_free(&ictx->first_pkt);
+  if (ictx->flush_pkt) av_packet_free(&ictx->flush_pkt);
   if (ictx->ac) avcodec_free_context(&ictx->ac);
   if (ictx->vc && (AV_HWDEVICE_TYPE_NONE == ictx->hw_type)) avcodec_free_context(&ictx->vc);
   for (int i = 0; i < nb_outputs; i++) {