[FFmpeg-devel] [PATCHv2 2/3] avformat/utils: increase detected start_time with skip_samples

[wm4]

On Tue,  8 Mar 2016 21:29:52 +0100
Marton Balint <cus at passwd.hu> wrote:

> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  libavformat/utils.c               | 10 ++++--
>  tests/ref/fate/gapless2-ipod-aac1 | 72 +++++++++++++++++++--------------------
>  tests/ref/fate/gapless2-ipod-aac2 | 72 +++++++++++++++++++--------------------
>  3 files changed, 80 insertions(+), 74 deletions(-)
> 
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index f4ae8b4..bb1c290 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -971,8 +971,11 @@ static void update_initial_timestamps(AVFormatContext *s, int stream_index,
>          if (is_relative(pktl->pkt.dts))
>              pktl->pkt.dts += shift;
>  
> -        if (st->start_time == AV_NOPTS_VALUE && pktl->pkt.pts != AV_NOPTS_VALUE)
> +        if (st->start_time == AV_NOPTS_VALUE && pktl->pkt.pts != AV_NOPTS_VALUE) {
>              st->start_time = pktl->pkt.pts;
> +            if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO && st->codec->sample_rate)
> +                st->start_time += av_rescale_q(st->skip_samples, (AVRational){1, st->codec->sample_rate}, st->time_base);
> +        }
>  
>          if (pktl->pkt.pts != AV_NOPTS_VALUE && delay <= MAX_REORDER_DELAY && has_decode_delay_been_guessed(st)) {
>              pts_buffer[0] = pktl->pkt.pts;
> @@ -983,8 +986,11 @@ static void update_initial_timestamps(AVFormatContext *s, int stream_index,
>          }
>      }
>  
> -    if (st->start_time == AV_NOPTS_VALUE)
> +    if (st->start_time == AV_NOPTS_VALUE) {
>          st->start_time = pts;
> +        if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO && st->codec->sample_rate)
> +            st->start_time += av_rescale_q(st->skip_samples, (AVRational){1, st->codec->sample_rate}, st->time_base);
> +    }
>  }

I'm a probably bit late here, but what's the rationale of increasing the
start time?

Maybe it's like this: the first packet has a negative timestamp, so
utils.c sets the start_time to something negative, so this has to be
compensated again so that the start time is 0?