[Libav-user] Using libav to insert silence at the beginning of an audio clip

[Chris Hennes]

I started with adelay=1000|1000,atrim... and expected that to give me one second of silence  (for a stereo track), but it did not. I take it that it should have, so I should go back to debugging that? I gave up on it when I couldn't make sense of the output.
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From: Libav-user <libav-user-bounces at ffmpeg.org> on behalf of Paul B Mahol <onemda at gmail.com>
Sent: Tuesday, March 21, 2017 10:53:15 AM
To: This list is about using libavcodec, libavformat, libavutil, libavdevice and libavfilter.
Subject: Re: [Libav-user] Using libav to insert silence at the beginning of an audio clip

On 3/21/17, Chris Hennes <chennes at pioneerlibrarysystem.org> wrote:
> The software I am writing allows a user to combine multiple
> potentially-overlapping audio clips by specifying an in and out point for
> each clip, plus when in the final stream that clip starts. I'm trying to
> string together a single filter graph that will do this and am struggling
> with the start point bit. My thought was to take each of the audio files and
> construct a filter chain for them that inserts silence of the required
> length at the beginning, then the atrim'ed audio clip, then an apad to the
> end of the required length, so (for just a single audio file), something
> like:
>
> (some kind of silence-generator here)[delay0];[in0]atrim=start=1:end=3,apad
> [end0];[delay0][end0]concat=n=2,v=0,a=1[final0]
>
> I can't seem to figure out how to make the concat work, though. No matter
> what technique I use to generate the silence (or non-silence, I've tried
> using sine and anoisesrc), I am getting an "invalid argument". I've tried
> playing around with the ffmpeg exe on the command line, but still can't make
> heads or tails of concat. What am I missing? Or is there a better way to do
> what I am describing?
>

Yes, see adelay filter.
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