[FFmpeg-devel] [PATCH] avformat/hls Implement support for using AVSEEK_FLAG_BACKWARD when seeking

[徐慧书]

On Sat, May 15, 2021 at 4:11 AM Gustav Grusell <gustav.grusell at gmail.com> wrote:
>
> Before, seeking in hls streams would always seek to the next keyframe after the given timestamp.
> With this fix, if AVSEEK_FLAG_BACKWARD is set, seeking will be to the first keyframe of the
> segment containing the given timestamp. This fixes #6850.
> ---
>  libavformat/hls.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/libavformat/hls.c b/libavformat/hls.c
> index 8fc6924c90..3f1fd2cb70 100644
> --- a/libavformat/hls.c
> +++ b/libavformat/hls.c
> @@ -2199,10 +2199,15 @@ static int hls_read_packet(AVFormatContext *s, AVPacket *pkt)
>
>                      tb = get_timebase(pls);
>                      ts_diff = av_rescale_rnd(pls->pkt->dts, AV_TIME_BASE,
> -                                            tb.den, AV_ROUND_DOWN) -
> -                            pls->seek_timestamp;
> -                    if (ts_diff >= 0 && (pls->seek_flags  & AVSEEK_FLAG_ANY ||
> -                                        pls->pkt->flags & AV_PKT_FLAG_KEY)) {
> +                                             tb.den, AV_ROUND_DOWN) -
> +                              pls->seek_timestamp;
> +                    /* If AVSEEK_FLAG_BACKWARD set and not AVSEEK_FLAG_ANY,
> +                     * we return the first keyframe encountered */
> +                    if ((pls->seek_flags & AVSEEK_FLAG_BACKWARD &&
> +                         !(pls->seek_flags & AVSEEK_FLAG_ANY) &&
> +                         pls->pkt->flags & AV_PKT_FLAG_KEY) ||
> +                        (ts_diff >= 0 && (pls->seek_flags  & AVSEEK_FLAG_ANY ||
> +                                          pls->pkt->flags & AV_PKT_FLAG_KEY))) {
>                          pls->seek_timestamp = AV_NOPTS_VALUE;
>                          break;
>                      }



I think you can put your code above this line ( tb =
get_timebase(pls). )  to avoid invalid code execution and keep the
code aligned

Regards,
bevis