[FFmpeg-devel] One pass volume normalization (ebur128)

Nicolas George nicolas.george at normalesup.org
Tue Jul 16 15:36:31 CEST 2013

L'octidi 28 messidor, an CCXXI, Jan Ehrhardt a écrit :
> No, that is no deep misunderstanding. On a SD card, you really do not
> want to use FFMpeg's logs, because they slow down things terribly. For
> instance, volume detection on a concatenated stream of 2 2GB Sony
> Camcorder files takes 17 seconds with no logging and 27 seconds with
> logging. Redirecting the screen output (stderr) to a file is 40% faster
> than using the log.

It seems clear to me your problem here is of system programming:
establishing pipes with auxiliary processes to get their output without
writing to a temporary file nor using "screen output" (and slightly more
subtle: get two output streams from the same program without blocking).

> I thought that would be obvious.

I thought it would be obvious that, to measure the speed of a process, you
try to isolate this process as much as possible, not drown within unrelated

> Sometimes you do want volumedetect on concatenated audio, sometimes you
> do not. In my case, the first recording is often a short intro on what
> the interview with the client will be about. It is very often taken
> under different sound conditions than the remainder of the recording(s).
> I have seen people recording the introduction inside a car before
> entering a house et cetera.

That is reasonable, but I do not see that it creates additional difficulty.

> PS. With respect to the slowness of writing to SD cards see this patch:
> https://github.com/FFmpeg/FFmpeg/commit/f4d9148fe282879b9fcc755767c9c04de9ddbcfa
> By simply increasing the copy-buffer from 1K to 32K qt-faststart became
> 400 times as fast.

It seems to me this is a sign of a crappy (or badly configured) operating
system, but it is completely unrelated to the problem at hand since there is
absolutely nothing to write in any permanent file until the final phase.


  Nicolas George
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