Re: [FFmpeg-devel] [PATCH v2 2/2] ffmpeg: fix implementation of updated input start time

[Gyan Doshi <ffmpeg@gyani.pro>]

Ping.

On 2022-10-21 10:01 pm, Gyan Doshi wrote:
> The current adjustment of input start times just adjusts the tsoffset.
> And it does so, by resetting the tsoffset to nullify the new start time.
> This leads to breakage of -copyts, ignoring of input_ts_offset, breaking
> of -isync as well as breaking wrap correction.
>
> Fixed by taking cognizance of these parameters, and by correcting start times
> just before sync offsets are applied.
> ---
>   fftools/ffmpeg.c       |  2 +-
>   fftools/ffmpeg.h       |  5 ++++-
>   fftools/ffmpeg_demux.c |  4 ++--
>   fftools/ffmpeg_opt.c   | 33 +++++++++++++++++++++++----------
>   4 files changed, 30 insertions(+), 14 deletions(-)
>
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index 0fe582be3b..c564b2649e 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -1815,7 +1815,7 @@ static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *p
>           start_time = 0;
>           if (copy_ts) {
>               start_time += f->start_time != AV_NOPTS_VALUE ? f->start_time : 0;
> -            start_time += start_at_zero ? 0 : f->ctx->start_time;
> +            start_time += start_at_zero ? 0 : f->start_time_effective;
>           }
>           if (ist->pts >= f->recording_time + start_time) {
>               close_output_stream(ost);
> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
> index 5966cac60e..2d97ccaa15 100644
> --- a/fftools/ffmpeg.h
> +++ b/fftools/ffmpeg.h
> @@ -447,7 +447,10 @@ typedef struct InputFile {
>       AVRational time_base; /* time base of the duration */
>       int64_t input_ts_offset;
>       int input_sync_ref;
> -
> +    /**
> +     * Effective format start time based on enabled streams.
> +     */
> +    int64_t start_time_effective;
>       int64_t ts_offset;
>       /**
>        * Extra timestamp offset added by discontinuity handling.
> diff --git a/fftools/ffmpeg_demux.c b/fftools/ffmpeg_demux.c
> index 6e89f5999a..220fda56da 100644
> --- a/fftools/ffmpeg_demux.c
> +++ b/fftools/ffmpeg_demux.c
> @@ -120,7 +120,7 @@ static int seek_to_start(InputFile *ifile)
>   static void ts_fixup(InputFile *ifile, AVPacket *pkt, int *repeat_pict)
>   {
>       InputStream *ist = input_streams[ifile->ist_index + pkt->stream_index];
> -    const int64_t start_time = ifile->ctx->start_time;
> +    const int64_t start_time = ifile->start_time_effective;
>       int64_t duration;
>   
>       if (debug_ts) {
> @@ -367,7 +367,7 @@ int ifile_get_packet(InputFile *f, AVPacket **pkt)
>       if (f->readrate || f->rate_emu) {
>           int i;
>           int64_t file_start = copy_ts * (
> -                              (f->ctx->start_time != AV_NOPTS_VALUE ? f->ctx->start_time * !start_at_zero : 0) +
> +                              (f->start_time_effective != AV_NOPTS_VALUE ? f->start_time_effective * !start_at_zero : 0) +
>                                 (f->start_time != AV_NOPTS_VALUE ? f->start_time : 0)
>                                );
>           float scale = f->rate_emu ? 1.0 : f->readrate;
> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> index 28b7d4dc27..a6fa9b7801 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -216,13 +216,15 @@ int parse_and_set_vsync(const char *arg, int *vsync_var, int file_idx, int st_id
>       return 0;
>   }
>   
> +/* Correct input file start times based on enabled streams */
>   static void correct_input_start_times(void)
>   {
> -    // Correct starttime based on the enabled streams
>       for (int i = 0; i < nb_input_files; i++) {
>           InputFile       *ifile = input_files[i];
>           AVFormatContext    *is = ifile->ctx;
> -        int64_t new_start_time = INT64_MAX;
> +        int64_t new_start_time = INT64_MAX, diff, abs_start_seek;
> +
> +        ifile->start_time_effective = is->start_time;
>   
>           if (is->start_time == AV_NOPTS_VALUE ||
>               !(is->iformat->flags & AVFMT_TS_DISCONT))
> @@ -234,9 +236,20 @@ static void correct_input_start_times(void)
>                   continue;
>               new_start_time = FFMIN(new_start_time, av_rescale_q(st->start_time, st->time_base, AV_TIME_BASE_Q));
>           }
> -        if (new_start_time > is->start_time) {
> -            av_log(is, AV_LOG_VERBOSE, "Correcting start time by %"PRId64"\n", new_start_time - is->start_time);
> -            ifile->ts_offset = -new_start_time;
> +
> +        diff = new_start_time - is->start_time;
> +        if (diff) {
> +            av_log(NULL, AV_LOG_VERBOSE, "Correcting start time of Input #%d by %"PRId64" us.\n", i, diff);
> +            ifile->start_time_effective = new_start_time;
> +            if (copy_ts && start_at_zero)
> +                ifile->ts_offset = -new_start_time;
> +            else if (!copy_ts) {
> +                abs_start_seek = is->start_time + (ifile->start_time != AV_NOPTS_VALUE) ? ifile->start_time : 0;
> +                ifile->ts_offset = abs_start_seek > new_start_time ? -abs_start_seek : -new_start_time;
> +            } else if (copy_ts)
> +                ifile->ts_offset = 0;
> +
> +            ifile->ts_offset += ifile->input_ts_offset;
>           }
>       }
>   }
> @@ -269,9 +282,9 @@ static int apply_sync_offsets(void)
>           if (self->ctx->start_time_realtime != AV_NOPTS_VALUE && ref->ctx->start_time_realtime != AV_NOPTS_VALUE) {
>               self_start_time = self->ctx->start_time_realtime;
>               ref_start_time  =  ref->ctx->start_time_realtime;
> -        } else if (self->ctx->start_time != AV_NOPTS_VALUE && ref->ctx->start_time != AV_NOPTS_VALUE) {
> -            self_start_time = self->ctx->start_time;
> -            ref_start_time  =  ref->ctx->start_time;
> +        } else if (self->start_time_effective != AV_NOPTS_VALUE && ref->start_time_effective != AV_NOPTS_VALUE) {
> +            self_start_time = self->start_time_effective;
> +            ref_start_time  =  ref->start_time_effective;
>           } else {
>               start_times_set = 0;
>           }
> @@ -1918,8 +1931,6 @@ int ffmpeg_parse_options(int argc, char **argv)
>           goto fail;
>       }
>   
> -    apply_sync_offsets();
> -
>       /* create the complex filtergraphs */
>       ret = init_complex_filters();
>       if (ret < 0) {
> @@ -1936,6 +1947,8 @@ int ffmpeg_parse_options(int argc, char **argv)
>   
>       correct_input_start_times();
>   
> +    apply_sync_offsets();
> +
>       check_filter_outputs();
>   
>   fail:

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