On 11/26/2020 5:52 AM, Ram Shaffir wrote:
From: ffmpeg-user <ffmpeg-user-boun...@ffmpeg.org> On Behalf Of Ram
Shaffir
Sent: Thursday, November 26, 2020 2:53 PM
Is it possible to combine the following three calls into one call instead?
ffmpeg -y -f concat -safe 0 -copyts -i videoList.txt -muxpreload 0 -muxdelay 0
-c copy -b:a 128K -cpu-used 0 -preset slow -movflags +faststart -f mp4
concat.mp4
Make one file out of ??? files. Does this also re-encode anything? (What are
the input formats? see below)
ffmpeg -y -i concat.mp4 -itsoffset 1.9 -i concat.mp4 -c:a aac -c:v copy -map
0:v:0 -map 1:a:0 -f mp4 audioFixed.mp4
Shift the audio a bit and re-mux.
ffmpeg -y -i audioFixed.mp4 -ss 2 -to 17 -c:v copy -c:a aac -f mp4 final.mp4
Select part of the now-shifted file.
Sometimes, there is no gain to creating more complex directives. In this
case, it might reduce the amount of de/remux work, but the time-shift
suggests pretty much means you're stuck with intermediate file(s). Might
combine the 2nd and 3rd commands.
Since you only select 17 seconds from the output, you could add a 20 second
limit to the first step, which would potentially make the intermediate files
smaller. (Another thing we don't know.)
Consider using another _container_ type for the intermediate file(s) (e.g.
nut, avi, or mkv, which can hold the mp4 data).
You could also, in the first pass, write to separate files for audio and
video, which might simplify the shift/remux process and then apply the
time-based selection to that (see
https://trac.ffmpeg.org/wiki/Creating%20multiple%20outputs).
Move the "faststart" to the last step since that's where it would matter (it
gets in the way of piping, if used, and it adds a second file write pass).
I haven't yet tried any of this, and there's probably an error somewhere in
there.
As usual, it really helps to see the command output so we know the file
formats/etc.
z!
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