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

[Linjie Fu]

Hi Gyan,
On Sun, Jul 18, 2021 at 12:24 PM Gyan Doshi <ffmpeg at gyani.pro> wrote:
>
>
>
> On 2021-07-18 09:32, Linjie Fu wrote:
> > On Wed, Jul 7, 2021 at 9:42 AM Linjie Fu <linjie.justin.fu at gmail.com> wrote:
> >> 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.
> >>
> > Another ping, thx.
>
> I pushed changes to this code yesterday. I don't think it's required
> anymore, but do test.
>

Thanks for the review, tested after applying the readrate patch, I'm
afraid that it's not identical as hope,
since ist->nb_packets would increase no matter input stream got output or not:

(lldb) p ist->nb_packets
(uint64_t) $4 = 1

(lldb) p ist->got_output
(int) $5 = 0

Hence we still need to add the check for  ist->got_output, or replace
the ist->nb_packets.
Also there is a new warning caught by the check in patchwork, probably
"mixed declaration and code warning".
Will send patches to rebase and fix.

- linjie