[FFmpeg-devel] [PATCH] libavfilter/af_showvolume: A Simple Audio Filter for Extracting Volume Information

Lars Kiesow lkiesow at uos.de
Wed Dec 24 00:57:07 CET 2014

Hi Stefano,
my first idea was to have ffmpeg generate the image but you are right,
that the unknown length is a problem. The only solution I could come up
with was to have something like a two-pass encoding so that you know
how many samples you have to deal with and in the second run generate
the image.

But then I thought that is not worth the effort since it's really easy
to just dump the data into something like gnuplot which is well tested
and much more flexible than doing things on your own :)

As I wrote already, I found another solution thanks to wm4 but maybe I
will have a look at the signalstats filter anyway. In any case: Thanks
for the hint.


On Tue, 23 Dec 2014 08:38:54 +0100
Stefano Sabatini <stefasab at gmail.com> wrote:

> I think a better approach would be to export the average per-frame
> volume to the metadata. Then you can use ffprobe to show such values
> and process them. Parsing the log is not robust.
> Also you could extend one of the existing filters to do that, or
> design a new audio filter based on signalstats (it could be
> named 'asignalstats').
> Also, I think ideally we should be able to generate an output showing
> as an image directly from ffmpeg (but could be more tricky due to the
> undefined length of an audio track).

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