[FFmpeg-devel] [PATCH] ffmpeg: Do not fill gap before the first decodable frame on single stream input files in CFR mode.

[Michael Niedermayer]

Fixes different behavior to JM and probably several if not all
reference decoders.

We cannot just do this unconditionally as it would ruin AV sync in
some use cases.

Bug-Found-by: BugMaster
Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
---
 ffmpeg.c     |   10 ++++++++++
 ffmpeg.h     |    1 +
 ffmpeg_opt.c |    1 +
 3 files changed, 12 insertions(+)

diff --git a/ffmpeg.c b/ffmpeg.c
index 2a88535..be3513e 100644
--- a/ffmpeg.c
+++ b/ffmpeg.c
@@ -824,6 +824,16 @@ static void do_video_out(AVFormatContext *s,
         } else
             format_video_sync = (s->oformat->flags & AVFMT_VARIABLE_FPS) ? ((s->oformat->flags & AVFMT_NOTIMESTAMPS) ? VSYNC_PASSTHROUGH : VSYNC_VFR) : VSYNC_CFR;
     }
+    if (   ist
+        && format_video_sync == VSYNC_CFR
+        && input_files[ist->file_index]->ctx->nb_streams == 1
+        && input_files[ist->file_index]->input_ts_offset == 0
+        && ost->frame_number == 0
+        && delta - duration >= 0.5) {
+        av_log(NULL, AV_LOG_DEBUG, "Not duplicating %d initial frames\n", (int)lrintf(delta - duration));
+        delta = duration;
+        ost->sync_opts = lrint(sync_ipts);
+    }
 
     switch (format_video_sync) {
     case VSYNC_CFR:
diff --git a/ffmpeg.h b/ffmpeg.h
index 409525c..8e42e26 100644
--- a/ffmpeg.h
+++ b/ffmpeg.h
@@ -281,6 +281,7 @@ typedef struct InputFile {
     int eof_reached;      /* true if eof reached */
     int eagain;           /* true if last read attempt returned EAGAIN */
     int ist_index;        /* index of first stream in input_streams */
+    int64_t input_ts_offset;
     int64_t ts_offset;
     int64_t last_ts;
     int64_t start_time;   /* user-specified start time in AV_TIME_BASE or AV_NOPTS_VALUE */
diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
index 23e1c40..8da1ce4 100644
--- a/ffmpeg_opt.c
+++ b/ffmpeg_opt.c
@@ -852,6 +852,7 @@ static int open_input_file(OptionsContext *o, const char *filename)
     f->ist_index  = nb_input_streams - ic->nb_streams;
     f->start_time = o->start_time;
     f->recording_time = o->recording_time;
+    f->input_ts_offset = o->input_ts_offset;
     f->ts_offset  = o->input_ts_offset - (copy_ts ? 0 : timestamp);
     f->nb_streams = ic->nb_streams;
     f->rate_emu   = o->rate_emu;
-- 
1.7.9.5