[FFmpeg-user] How to add padding silence for MP4 container?

Paul B Mahol onemda at gmail.com
Sat May 25 15:21:57 CEST 2013

On 5/25/13, Liam Condron-Farnos <23liam at googlemail.com> wrote:
> On 25 May 2013 13:45, Tom Horsley <horsley1953 at gmail.com> wrote:
>>> So instead of using timestamps with MP4, is there a way to tell ffmpeg
>>> to
>>> insert 2s of silence at the beginning of the audio?
>> I don't know about using ffmpeg itself, but I fiddle with audio
>> sync problems all the time and I use sox to generate silence
>> when I need it. For example:
> To generate silence with ffmpeg, use the aevalsrc audio filter
> http://ffmpeg.org/ffmpeg-all.html#aevalsrc
> Then, you can use either the concat demuxer (for which you'll have to
> generate the sound separately, ad then prepend it to your existing
> audio in two distinct commands) or the concat filter (requires
> re-encoding, but will allow you to work with a single ffmpeg command).
> ffmpeg -filter_complex 'aevalsrc=0:d=2' silence.aac
> ffmpeg -f concat -i <(for f in silence.aac audio.aac; do echo file
> "'$f'"; done) -c copy out-audio.aac
> OR:
> ffmpeg -i audio.aac  -filter_complex
> 'aevalsrc=0:d=2[slug];[slug][0]concat=n=2:v=0:a=1[out]' -map '[out]'
> -c:a libfdk_aac -vbr 3 out-audio.aac
> (change depending on the AAC encoder you have)
> http://ffmpeg.org/trac/ffmpeg/wiki/How to concatenate (join, merge) media
> files

That is veeery complicated way to do something when there is very fast
and easy way.

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