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

[Shiwang.Xie]

Ping.

Thanks,
Shiwang.Xie

On Sat, 29 May 2021, Shiwang.Xie wrote:

> Hi, any updates for this?
>
> Thanks,
> Shiwang.Xie
>
> On Wed, 19 May 2021, Shiwang.Xie wrote:
>
>> Hi, is there objection?
>> 
>> Thanks,
>> Shiwang.Xie
>> 
>> On Sat, 15 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(-)
>>> 
>>> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
>>> index b3658d8f65..309d9dfa6e 100644
>>> --- a/fftools/ffmpeg.c
>>> +++ b/fftools/ffmpeg.c
>>> @@ -2082,9 +2082,11 @@ static void do_streamcopy(InputStream *ist, 
>>> OutputStream *ost, const AVPacket *p
>>>     }
>>>
>>>     if (f->recording_time != INT64_MAX) {
>>> -        start_time = f->ctx->start_time;
>>> -        if (f->start_time != AV_NOPTS_VALUE && copy_ts)
>>> -            start_time += f->start_time;
>>> +        start_time = 0;
>>> +        if (copy_ts) {
>>> +            start_time += f->start_time != AV_NOPTS_VALUE ? f->start_time 
>>> : 0;
>>> +            start_time += start_at_zero ? 0 : f->ctx->start_time;
>>> +        }
>>>         if (ist->pts >= f->recording_time + start_time) {
>>>             close_output_stream(ost);
>>>             return;
>>> -- 
>>> 2.18.5
>>> 
>>> 
>> 
>