Re: [SoX-users] Piping problems with MP3 on XP

[Jan S. <ha...@st...>]

> > On my installation, the following works
> > (where the output of faad is indeed of the specified format
> > - edit for your format):
> > 
> > faad -q -w in.mp4 | sox -V -t raw -r 44100 -b 16 -c 2 -e signed - out.wav
> 
> I think there is a subtle problem with this because faad emits MS wav
> pcm. Interpreting that as raw would mix wav meta data with the audio.
> The right enchantment (according to faad(1)) then becomes:
> 
> faad -w -f 2 in.mp4 | sox -V -t raw -r 44100 -b 16 -c 2 -e signed - out.wav

Yes, you are right. 'faad -w' writes a WAV file to stdout,
while 'faad -f2' writes the raw data to stdout.

$ file in.mp4
in.mp4: ISO Media, MPEG v4 system, version 2

$ faad -w in.mp4 > out.wav
$ file out.wav
out.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz
$ soxi out.wav

Input File     : 'out.wav'
Channels       : 2
Sample Rate    : 44100
Precision      : 16-bit
Sample Encoding: 16-bit Signed Integer PCM


So it is really a WAV that goes to stdout,
and sox correctly recognizes it:

hans@mac:~$ faad -w in.mp4 | sox -V - out.wav
 *********** Ahead Software MPEG-4 AAC Decoder V2.7 ******************

 Build: Sep  9 2010
 Copyright 2002-2004: Ahead Software AG
 http://www.audiocoding.com
 Floating point version

 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License.

 **************************************************************************

in.mp4 file info:

LC AAC	2.900 secs, 2 ch, 44100 Hz

tool: FAAC 1.28

  ---------------------
 | Config:  2 Ch       |
  ---------------------
 | Ch |    Position    |
  ---------------------
 | 00 | Left front     |
 | 01 | Right front    |
  ---------------------

0% decoding in.mp4.1% decoding in.mp4.2% decoding in.mp4.3% decoding in.mp4.4% decoding in.mp4.5% decoding in.mp4.6% decoding in.mp4.sox: SoX v14.3.2
sox INFO formats: detected file format type `wav'

Input File     : '-' (wav)
Channels       : 2
Sample Rate    : 44100
Precision      : 16-bit
Sample Encoding: 16-bit Signed Integer PCM
Endian Type    : little
Reverse Nibbles: no
Reverse Bits   : no

sox INFO sox: Overwriting `out.wav'

Output File    : 'out.wav'
Channels       : 2
Sample Rate    : 44100
Precision      : 16-bit
Sample Encoding: 16-bit Signed Integer PCM
Endian Type    : little
Reverse Nibbles: no
Reverse Bits   : no
Comment        : 'Processed by SoX'

sox INFO sox: effects chain: input      44100Hz 2 channels
sox INFO sox: effects chain: output     44100Hz 2 channels


What puzzles me is that the out.wav so produced is incorrect;
namely, the header does not even include a duration. After doing

$ sox --ignore-length out.wav good.wav

the resulting good.wav is a correct WAV file, with the correct
duration stored in the header.


Also, if I explicitly tell sox about the stdin format

$ faad -w in.mp4 | sox -V -t raw -r 44100 -e signed -b 16 -c 2 - out.wav

(which is WRONG, because the '-' is not raw, it's a WAV)
then the out.wav so produced is correct.


	Jan