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

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2023-01-03 03:52 pm, Gyan Doshi wrote:
> 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.

Comments?

> ---
> 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;

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