[FFmpeg-devel] [PATCH v2] fftools/ffmpeg: accelerate seeking while reading input at native frame rate

[Linjie Fu]

On Sun, Jul 4, 2021 at 10:50 PM Linjie Fu <fulinjie at zju.edu.cn> wrote:
>
> From: Linjie Fu <linjie.justin.fu at gmail.com>
>
> Skip the logic of frame rate emulation until the input reaches the
> specified start time.
>
> Test CMD:
>    $ffmpeg -re -ss 30 -i input.mp4 -pix_fmt yuv420p -f sdl2 -
>
> Before the patch:
> first time to got frame, it takes 257305 us
> After this patch:
> first time to got frame, it takes 48879 us
>
> Signed-off-by: Linjie Fu <linjie.justin.fu at gmail.com>
> ---
> [v2]: fixed the mixed declaration and code warning
> Calculate the time to get the first frame:
> https://github.com/fulinjie/ffmpeg/commit/2aa4762e1e65709997b1ab9dd596332244db80ed
>  fftools/ffmpeg.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index e97d879cb3..c8849e4250 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -4221,10 +4221,14 @@ static int get_input_packet(InputFile *f, AVPacket **pkt)
>  {
>      if (f->rate_emu) {
>          int i;
> +        int64_t pts;
> +        int64_t now;
>          for (i = 0; i < f->nb_streams; i++) {
>              InputStream *ist = input_streams[f->ist_index + i];
> -            int64_t pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
> -            int64_t now = av_gettime_relative() - ist->start;
> +            if (!ist->got_output)
> +                continue;
> +            pts = av_rescale(ist->dts, 1000000, AV_TIME_BASE);
> +            now = av_gettime_relative() - ist->start;
>              if (pts > now)
>                  return AVERROR(EAGAIN);
>          }
> --
> 2.31.1
ping, thx.

- linjie