[FFmpeg-user] Questions about the concat video filter

Katherine Frances knfrances at gmail.com
Wed Jan 24 00:40:49 EET 2018

Kia ora Dave,

> Some audio encodings don’t support arbitrary sample counts, so it’s not uncommon that the audio and video encodings of a file has minor fluctuations in their duration. Also video and audio sampling rates often has different timebases so it’s usually not feasible for their durations to be the same. For instance you may have a second of 48000 Hz audio, but it is not possible to have one second of an NTSC (30000/1001 fps) recording.
> So for instance concatenating a segment of video + audio with another segment of video + audio would be more accurate, then concatenating 2 audio encodings and separately concatenating 2 video encodings and then hopefully that they will still align.

Yes, it makes total sense that audio & video streams should be
specified as such, so that everything stays in step. Thank you for the

> No unless you provide that black slug. In this case the duration of the last frame will be longer to cover the missing video.

Thanks. That command is a perfect demo.

> If you know what you want the output to be then you should clarify, otherwise it leaves the guesswork to ffmpeg which may or may not be want you want.

Haha, got it.

Cheers Dave, I really appreciate your thoughtful answers!

Best, K

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