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

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2022-09-27 10:10 am, 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 user_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.

Comments?

> ---
>   fftools/ffmpeg.c       | 24 +-------------------
>   fftools/ffmpeg.h       |  5 ++++-
>   fftools/ffmpeg_demux.c |  4 ++--
>   fftools/ffmpeg_opt.c   | 50 +++++++++++++++++++++++++++++++++++++-----
>   4 files changed, 52 insertions(+), 31 deletions(-)
>
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index 0e1477299d..fabb0fb952 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -1898,7 +1898,7 @@ 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->enabled_start_time;
>           }
>           if (ist->pts >= f->recording_time + start_time) {
>               close_output_stream(ost);
> @@ -3323,28 +3323,6 @@ static int transcode_init(void)
>                   input_streams[j + ifile->ist_index]->start = av_gettime_relative();
>       }
>   
> -    // Correct starttime based on the enabled streams
> -    for (i = 0; i < nb_input_files; i++) {
> -        InputFile       *ifile = input_files[i];
> -        AVFormatContext    *is = ifile->ctx;
> -        int64_t new_start_time = INT64_MAX;
> -
> -        if (is->start_time == AV_NOPTS_VALUE ||
> -            !(is->iformat->flags & AVFMT_TS_DISCONT))
> -            continue;
> -
> -        for (int j = 0; j < is->nb_streams; j++) {
> -            AVStream *st = is->streams[j];
> -            if(st->discard == AVDISCARD_ALL || st->start_time == AV_NOPTS_VALUE)
> -                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;
> -        }
> -    }
> -
>       /* init input streams */
>       for (i = 0; i < nb_input_streams; i++)
>           if ((ret = init_input_stream(i, error, sizeof(error))) < 0)
> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
> index ede0b2bd96..b93c2427b6 100644
> --- a/fftools/ffmpeg.h
> +++ b/fftools/ffmpeg.h
> @@ -439,7 +439,10 @@ 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 enabled_start_time;
>       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..6125181f81 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->enabled_start_time;
>       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->enabled_start_time != AV_NOPTS_VALUE ? f->enabled_start_time * !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 5febe319e4..8df322c31c 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -293,6 +293,44 @@ static int parse_and_set_vsync(const char *arg, int *vsync_var, int file_idx, in
>       return 0;
>   }
>   
> +/* Correct input file start times based on enabled streams */
> +static int correct_input_start_times(void)
> +{
> +    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, diff, abs_start_seek;
> +
> +        ifile->enabled_start_time = is->start_time;
> +
> +        if (is->start_time == AV_NOPTS_VALUE ||
> +            !(is->iformat->flags & AVFMT_TS_DISCONT))
> +            continue;
> +
> +        for (int j = 0; j < is->nb_streams; j++) {
> +            AVStream *st = is->streams[j];
> +            if(st->discard == AVDISCARD_ALL || st->start_time == AV_NOPTS_VALUE)
> +                continue;
> +            new_start_time = FFMIN(new_start_time, av_rescale_q(st->start_time, st->time_base, AV_TIME_BASE_Q));
> +        }
> +
> +        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->enabled_start_time = 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;
> +            }
> +            ifile->ts_offset += ifile->input_ts_offset;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>   static int apply_sync_offsets(void)
>   {
>       for (int i = 0; i < nb_input_files; i++) {
> @@ -321,9 +359,9 @@ 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->enabled_start_time != AV_NOPTS_VALUE && ref->enabled_start_time != AV_NOPTS_VALUE) {
> +            self_start_time = self->enabled_start_time;
> +            ref_start_time  =  ref->enabled_start_time;
>           } else {
>               start_times_set = 0;
>           }
> @@ -3747,8 +3785,6 @@ int ffmpeg_parse_options(int argc, char **argv)
>           goto fail;
>       }
>   
> -    apply_sync_offsets();
> -
>       /* create the complex filtergraphs */
>       ret = init_complex_filters();
>       if (ret < 0) {
> @@ -3763,6 +3799,10 @@ int ffmpeg_parse_options(int argc, char **argv)
>           goto fail;
>       }
>   
> +    correct_input_start_times();
> +
> +    apply_sync_offsets();
> +
>       check_filter_outputs();
>   
>   fail:

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