[FFmpeg-devel] [PATCH] fftools/ffmpeg: fix -t inaccurate recording time

[Shiwang.Xie]

Is there objection? will push it tomorrow.

On Thu, 6 May 2021, Shiwang.Xie wrote:

>
> if input start time is not 0 -t is inaccurate doing stream copy,
> will record extra duration according to input start time.
> it should base on following cases:
>
> input video start time from 60s, duration is 300s,
> 1. stream copy:
>       ffmpeg -ss 40 -t 60 -i in.mp4 -c copy -y out.mp4
>   open_input_file() will seek to 100 and set ts_offset to -100,
>   process_input() will offset pkt->pts with ts_offset to make it 0,
>   so when do_streamcopy() with -t, exits when ist->pts >= recording_time.
>
> 2. stream copy with -copyts:
>       ffmpeg -ss 40 -t 60 -copyts -i in.mp4 -c copy -y out.mp4
>   open_input_file() will seek to 100 and set ts_offset to 0,
>   process_input() will keep raw pkt->pts as ts_offset is 0,
>   so when do_streamcopy() with -t, exits when
>   ist->pts >= (recording_time+f->start_time+f->ctx->start_time).
>
> 3. stream copy with -copyts -start_at_zero:
>       ffmpeg -ss 40 -t 60 -copyts -start_at_zero -i in.mp4 -c copy -y out.mp4
>   open_input_file() will seek to 120 and set ts_offset to -60 as start_to_zero option,
>   process_input() will offset pkt->pts with input file start time,
>   so when do_streamcopy() with -t, exits when ist->pts >= (recording_time+f->start_time).
>
> 0      60     40      60                     360
> |_______|_____|_______|_______________________|
>      start   -ss     -t
>
> This fixes ticket #9141.
>
> Signed-off-by: Shiwang.Xie <shiwang.xie666 at outlook.com>
> ---
> fftools/ffmpeg.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
>