[FFmpeg-devel] [PATCH] ffmpeg: apply discontinuity adjustment per-stream

[Gyan Doshi <ffmpeg@gyani.pro>]

At present, the offset for discontinuity adjustment is applied per-file but
the check for discontinuity is intra-stream so the same discontinuity when
seen in multiple streams with copyts, leads to compounded adjustment of the
discontinuity offset. This introduces gaps in streams, leading to loss of sync
or even de facto loss of stream.

The ts_offset_discont parameter is transferred to InputStream and adjusted
based on intra-stream gaps.
---
Here's a simulated example to demonstrate the issue:
1) generate input
ffmpeg -f lavfi -i nullsrc=s=32x32:r=1,format=gray -f lavfi -i anullsrc=cl=mono:r=8000 -c:v libx264 -preset superfast -bf 0 -crf 50 -c:a aac -b:a 64k -muxpreload 0 -muxdelay 0 -output_ts_offset 95000 -t 100000 src-100000s.ts

2) demo
ffmpeg -copyts -i "src-100000.ts" -vf "showinfo=checksum=0" -af "ashowinfo" -f null - -report

==Before patch==

timestamp discontinuity for stream #0:1 (id=257, type=audio): -95443717689, new offset= 95443717689
timestamp discontinuity for stream #0:0 (id=256, type=video): -95443717689, new offset= 190887435378

[Parsed_ashowinfo_0 @ 000002700af98800] n:0 pts:759998976 pts_time:94999.9
[Parsed_ashowinfo_0 @ 000002700af98800] n:1 pts:760000000 pts_time:95000
 ... 
[Parsed_ashowinfo_0 @ 000002700af98800] n:745202 pts:1523085824 pts_time:190386
[Parsed_ashowinfo_0 @ 000002700af98800] n:745203 pts:1523086848 pts_time:190386
[Parsed_ashowinfo_0 @ 000002700af98800] n:745204 pts:2286637614 pts_time:285830
[Parsed_ashowinfo_0 @ 000002700af98800] n:745205 pts:2286638638 pts_time:285830


[Parsed_showinfo_0 @ 000002700ec34700] n:   0 pts:8550000000 pts_time:95000
[Parsed_showinfo_0 @ 000002700ec34700] n:   1 pts:8550090000 pts_time:95001
 ... 
[Parsed_showinfo_0 @ 000002700ec34700] n:95380 pts:17134200000 pts_time:190380
[Parsed_showinfo_0 @ 000002700ec34700] n:95381 pts:17134290000 pts_time:190381
[Parsed_showinfo_0 @ 000002700ec34700] n:95382 pts:25724314592 pts_time:285826
[Parsed_showinfo_0 @ 000002700ec34700] n:95383 pts:25724404592 pts_time:285827

==After patch==

timestamp discontinuity for stream #0:1 (id=257, type=audio): -95443717689, new stream offset= 95443717689
timestamp discontinuity for stream #0:0 (id=256, type=video): -95443717689, new stream offset= 95443717689

[Parsed_ashowinfo_0 @ 0000023c773c8880] n:0 pts:759998976 pts_time:94999.9
[Parsed_ashowinfo_0 @ 0000023c773c8880] n:1 pts:760000000 pts_time:95000
 ... 
[Parsed_ashowinfo_0 @ 0000023c773c8880] n:745202 pts:1523085824 pts_time:190386
[Parsed_ashowinfo_0 @ 0000023c773c8880] n:745203 pts:1523086848 pts_time:190386
[Parsed_ashowinfo_0 @ 0000023c773c8880] n:745204 pts:1523087872 pts_time:190386
[Parsed_ashowinfo_0 @ 0000023c773c8880] n:745205 pts:1523088896 pts_time:190386


[Parsed_showinfo_0 @ 0000023c795d07c0] n:   0 pts:8550000000 pts_time:95000
[Parsed_showinfo_0 @ 0000023c795d07c0] n:   1 pts:8550090000 pts_time:95001
 ... 
[Parsed_showinfo_0 @ 0000023c795d07c0] n:95380 pts:17134200000 pts_time:190380
[Parsed_showinfo_0 @ 0000023c795d07c0] n:95381 pts:17134290000 pts_time:190381
[Parsed_showinfo_0 @ 0000023c795d07c0] n:95382 pts:17134380000 pts_time:190382
[Parsed_showinfo_0 @ 0000023c795d07c0] n:95383 pts:17134470000 pts_time:190383



 fftools/ffmpeg.c | 12 ++++++------
 fftools/ffmpeg.h |  8 ++++----
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index 881d6f0af2..b967055059 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -3418,13 +3418,13 @@ static void ts_discontinuity_detect(InputFile *ifile, InputStream *ist,
         if (fmt_is_discont) {
             if (FFABS(delta) > 1LL * dts_delta_threshold * AV_TIME_BASE ||
                 pkt_dts + AV_TIME_BASE/10 < FFMAX(ist->pts, ist->dts)) {
-                ifile->ts_offset_discont -= delta;
+                ist->ts_offset_discont -= delta;
                 av_log(NULL, AV_LOG_DEBUG,
                        "timestamp discontinuity for stream #%d:%d "
-                       "(id=%d, type=%s): %"PRId64", new offset= %"PRId64"\n",
+                       "(id=%d, type=%s): %"PRId64", new stream offset= %"PRId64"\n",
                        ist->file_index, ist->st->index, ist->st->id,
                        av_get_media_type_string(ist->par->codec_type),
-                       delta, ifile->ts_offset_discont);
+                       delta, ist->ts_offset_discont);
                 pkt->dts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
                 if (pkt->pts != AV_NOPTS_VALUE)
                     pkt->pts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
@@ -3447,10 +3447,10 @@ static void ts_discontinuity_detect(InputFile *ifile, InputStream *ist,
                fmt_is_discont && ifile->last_ts != AV_NOPTS_VALUE) {
         int64_t delta = pkt_dts - ifile->last_ts;
         if (FFABS(delta) > 1LL * dts_delta_threshold * AV_TIME_BASE) {
-            ifile->ts_offset_discont -= delta;
+            ist->ts_offset_discont -= delta;
             av_log(NULL, AV_LOG_DEBUG,
                    "Inter stream timestamp discontinuity %"PRId64", new offset= %"PRId64"\n",
-                   delta, ifile->ts_offset_discont);
+                   delta, ist->ts_offset_discont);
             pkt->dts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
             if (pkt->pts != AV_NOPTS_VALUE)
                 pkt->pts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
@@ -3463,7 +3463,7 @@ static void ts_discontinuity_detect(InputFile *ifile, InputStream *ist,
 static void ts_discontinuity_process(InputFile *ifile, InputStream *ist,
                                      AVPacket *pkt)
 {
-    int64_t offset = av_rescale_q(ifile->ts_offset_discont, AV_TIME_BASE_Q,
+    int64_t offset = av_rescale_q(ist->ts_offset_discont, AV_TIME_BASE_Q,
                                   ist->st->time_base);
 
     // apply previously-detected timestamp-discontinuity offset
diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
index 5527dbe49b..d7bba8a190 100644
--- a/fftools/ffmpeg.h
+++ b/fftools/ffmpeg.h
@@ -352,6 +352,10 @@ typedef struct InputStream {
     int64_t       next_pts;  ///< synthetic pts for the next decode frame (in AV_TIME_BASE units)
     int64_t       pts;       ///< current pts of the decoded frame  (in AV_TIME_BASE units)
     int           wrap_correction_done;
+    /**
+     * Extra timestamp offset added by discontinuity handling.
+     */
+    int64_t ts_offset_discont;
 
     // the value of AVCodecParserContext.repeat_pict from the AVStream parser
     // for the last packet returned from ifile_get_packet()
@@ -444,10 +448,6 @@ typedef struct InputFile {
      */
     int64_t start_time_effective;
     int64_t ts_offset;
-    /**
-     * Extra timestamp offset added by discontinuity handling.
-     */
-    int64_t ts_offset_discont;
     int64_t last_ts;
     int64_t start_time;   /* user-specified start time in AV_TIME_BASE or AV_NOPTS_VALUE */
     int64_t recording_time;
-- 
2.36.1

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