[FFmpeg-user] Is there a way to cut a video at an exact time ?

[Jim Worrall]

> On Apr 13, 2024, at 01:57, bbb <ffmpeg-user at bugblatterbeast.de> wrote:
> 
> Sorry for bothering you. It only behaves like this when I use "-codec copy". Without that option it accepts the exact time I've specified.
> 
> On 4/13/24 13:47, bbb wrote:
>> I want to cut off the start of a video. When I tell ffmpeg to start at an exact time, it refuses to do so and instead starts at a time that's somehow "convenient" for ffmpeg. I can only assume that it's probably depending on something like a keyframe or an important frame for the compression algorithm but I don't really know.
>> 
>> the command:
>> ffmpeg -ss 0:32.08 -i video.mkv -codec copy -map 0 video.cut.mkv
>> makes the output start around 0:31 (even when I change the parameter value a bit, the result is exactly the same).
>> 
>> Is there a way to make ffmpeg start at the exact time that I specified?
>> Does it maybe depend on the codec and would it help if I recode it before cutting?
>> 
>> It would be even better if I were able to start at a specific frame number but I didn't find a parameter to set that. To set a frame offset seems only possible when you're exporting to images.
>> _______________________________________________

I think this has everything you need to know.  Bottom line as I understand it: it’s not possible to cut video precisely while copying streams.
https://trac.ffmpeg.org/wiki/Seeking