[FFmpeg-user] FFmpeg accuracy issues.

[Shlomi Shalem]

I tried that as well:

'*ffmpeg -t 00:00:10.000 -analyzeduration 500000000  -i foo.wav
trimmed_foo.wav -ss 00:00:25.000'*
*
*
Full console output:

*ffmpeg version 0.11.1 Copyright (c) 2000-2012 the FFmpeg developers*
*  built on Jul 25 2012 19:55:05 with gcc 4.2.1 (Apple Inc. build 5664)*
*  configuration: --enable-gpl --enable-shared --enable-pthreads
--enable-libx264 --enable-libmp3lame*
*  libavutil      51. 54.100 / 51. 54.100*
*  libavcodec     54. 23.100 / 54. 23.100*
*  libavformat    54.  6.100 / 54.  6.100*
*  libavdevice    54.  0.100 / 54.  0.100*
*  libavfilter     2. 77.100 /  2. 77.100*
*  libswscale      2.  1.100 /  2.  1.100*
*  libswresample   0. 15.100 /  0. 15.100*
*  libpostproc    52.  0.100 / 52.  0.100*
*Guessed Channel Layout for  Input Stream #0.0 : mono*
*Input #0, wav, from 'foo.wav':*
*  Duration: 00:00:40.42, bitrate: 705 kb/s*
*    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono,
s16, 705 kb/s*
*File 'trimmed_foo.wav' already exists. Overwrite ? [y/N] y*
*Output #0, wav, to 'trimmed_foo.wav':*
*  Metadata:*
*    encoder         : Lavf54.6.100*
*    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono,
s16, 705 kb/s*
*Stream mapping:*
*  Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)*
*Press [q] to stop, [?] for help*
*size=     864kB time=00:00:10.03 bitrate= 705.6kbits/s    *
*video:0kB audio:864kB global headers:0kB muxing overhead 0.005199%*
*
*
Still didn't solve the problem. The output file is too long (even when I'm
checking it with another applications).


On Fri, Jul 27, 2012 at 5:46 PM, Michael Bradshaw <
mbradshaw at sorensonmedia.com> wrote:

> Please don't top post (if you need to you can google it).
>
> On Fri, Jul 27, 2012 at 8:27 AM, Shlomi Shalem <shlomi at shalem.co> wrote:
>
> > [...]
> >
> > As you can see, it didn't solve the problem. Am I misusing it? Any other
> > idea?
>
>
> Yeah, you're misusing it. Some files don't have the duration or other info
> stored in some header that FFmpeg can just parse. Some files, these things
> have to be guessed, and the only way to do that is to just read part of the
> file in. The more you read, the better your guess will be (if you read the
> whole file, you should have very accurate results). analyzeduration sets
> the amount that FFmpeg should read from the file in order to make the
> guesses it needs. Setting it to zero is like saying don't read it and just
> guess outright (iiuc). Setting it to a higher number allows FFmpeg to read
> more of the file. The default value is 5000000 (5MB).
>
> --Michael
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