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

[Shiwang.Xie]

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
>> 
>> 
>