[FFmpeg-user] Replacing First 90 Seconds of a Video with Silence or with Another Audio Clip

[Paul B Mahol]

On 1/17/16, Sam Logan <shapableline at gmail.com> wrote:
> I have a video AVI file, "Video.avi", consisting of a video and an audio
> track, and a separate audio file, "Audio.mp3". I want to do the following
> two things:
>
> (1)
>
> First, I want to produce a version of the video, "OutputSilenced.avi",
> which would be identical to the original video except that the first 90
> seconds of the video's audio are replaced with silence (to clarify, I want
> to REPLACE, as in overwrite, the first 90 seconds, NOT insert 90 seconds of
> silence to push the audio back 90 seconds).
>
> (2)
>
> Second, I want to produce a version of the video, "OutputReplaced.avi",
> which would be identical to the original video except that the first 90
> seconds of the video's audio are replaced with the first 90 seconds of
> "Audio.mp3" (again, to be clear, I want to REPLACE, as in overwrite, the
> first 90 seconds, NOT insert 90 seconds of audio to push the original audio
> back 90 seconds).
>
> How commands would I use to do this with FFmpeg? Ideally, I would like to
> just remux without doing any re-encoding. Thanks in advance.

With trimming original video's audio and using concat demuxer to
insert silence/audio.

So, some combination of trimming and concat demuxer.