[FFmpeg-devel] [PATCH] ffmpeg.c - drain all decoded frames during stream_loop flush

[Gyan Doshi]

Revised patch only drains 1 packet per call and loops via 
transcode_step() till EOF, just like when decoders are truly closed. 
Functionally the same result as first version.

On 3/15/2018 3:31 PM, Gyan Doshi wrote:
> Fixes a bug with flushing decoders during stream_loop. Note that the 
> issue is also averted if we skip flushing altogether.
-------------- next part --------------
From a19b5586ae343a2b36d9dce5a1343629ec0fb40f Mon Sep 17 00:00:00 2001
From: Gyan Doshi <gyandoshi at gmail.com>
Date: Thu, 15 Mar 2018 16:45:51 +0530
Subject: [PATCH v2] ffmpeg.c - drain all decoded frames during stream_loop
 flush

When a decoded stream is being looped, after each post-EOF rewind,
decoders are flushed in seek_to_start(). This only drains 1 frame, and
thus the output has a few frames missing at the tail of each iteration
except the last.

With this patch, process_input is looped till process_input_packet
reaches EOF.

Fixes #7081
---
 fftools/ffmpeg.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index ee7258fcd1..3c18e06713 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -4170,12 +4170,6 @@ static int seek_to_start(InputFile *ifile, AVFormatContext *is)
         ist   = input_streams[ifile->ist_index + i];
         avctx = ist->dec_ctx;
 
-        // flush decoders
-        if (ist->decoding_needed) {
-            process_input_packet(ist, NULL, 1);
-            avcodec_flush_buffers(avctx);
-        }
-
         /* duration is the length of the last frame in a stream
          * when audio stream is present we don't care about
          * last video frame length because it's not defined exactly */
@@ -4244,6 +4238,17 @@ static int process_input(int file_index)
         return ret;
     }
     if (ret < 0 && ifile->loop) {
+        AVCodecContext *avctx;
+        for (i = 0; i < ifile->nb_streams; i++) {
+            ist = input_streams[ifile->ist_index + i];
+            avctx = ist->dec_ctx;
+            if (ist->decoding_needed) {
+                ret = process_input_packet(ist, NULL, 1);
+                if (ret>0)
+                    return 0;
+                avcodec_flush_buffers(avctx);
+            }
+        }
         ret = seek_to_start(ifile, is);
         if (ret < 0)
             av_log(NULL, AV_LOG_WARNING, "Seek to start failed.\n");
-- 
2.12.2.windows.2