avformat/fifo: avoid repeated scaling of timestamps on failure and recovery

If fifo_thread_recover() succeeds immediately after
fifo_thread_dispatch_message() fails, the dts of the packet is scaled
twice, causing cur_dts to be abnormally large and "Application provided
invalid, non monotonically increasing dts to muxer in stream" to occur
repeatedly.

Steps to reproduce:
1. ffmpeg -f lavfi -i testsrc -c:v libx264 -map 0:v -flags +global_header -f fifo -fifo_format flv -attempt_recovery 1 -recover_any_error 1 rtmp://example.com/livekey
2. set a breakpoint on fifo_thread_recover
3. force disconnect from the rtmp server
4. wait for break
5. reconnect to the rtmp server
6. resume execution of ffmpeg

Signed-off-by: Ryoji Gyoda <gy.cft4@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/fifo.c

@@ -183,6 +183,7 @@ static int fifo_thread_write_packet(FifoThreadContext *ctx, AVPacket *pkt)
     AVFormatContext *avf2 = fifo->avf;
     AVRational src_tb, dst_tb;
     int ret, s_idx;
+    int64_t orig_pts, orig_dts, orig_duration;
 
     if (fifo->timeshift && pkt->dts != AV_NOPTS_VALUE)
         atomic_fetch_sub_explicit(&fifo->queue_duration, next_duration(avf, pkt, &ctx->last_received_dts), memory_order_relaxed);
@@ -198,14 +199,23 @@ static int fifo_thread_write_packet(FifoThreadContext *ctx, AVPacket *pkt)
         }
     }
 
+    orig_pts = pkt->pts;
+    orig_dts = pkt->dts;
+    orig_duration = pkt->duration;
     s_idx = pkt->stream_index;
     src_tb = avf->streams[s_idx]->time_base;
     dst_tb = avf2->streams[s_idx]->time_base;
     av_packet_rescale_ts(pkt, src_tb, dst_tb);
 
     ret = av_write_frame(avf2, pkt);
-    if (ret >= 0)
+    if (ret >= 0) {
         av_packet_unref(pkt);
+    } else {
+        // avoid scaling twice
+        pkt->pts = orig_pts;
+        pkt->dts = orig_dts;
+        pkt->duration = orig_duration;
+    }
     return ret;
 }