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

[Paul B Mahol]

On 3/21/17, Chris Hennes <chennes at pioneerlibrarysystem.org> wrote:
> 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.

That should give 1 second of silence at start of audio.

> ________________________________
> 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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