Re: [SoX-users] Reading a broken WAV file?

[Thor A. <th...@bi...>]

On Fri, May 28, 2010 at 07:54:58PM +0200, Chris Bagwell wrote:
> > On Sun, May 23, 2010 at 07:08:05PM +0000, Michael Chapman wrote:
> > 
> > [...]
> > 
> > > perpetuates the error.
> > > Not SoX's fault (I suspect the flavour of WAV it writes is limited
> > > to 4GB).
> > >
> > > IT WOULD BE NICE if SoX did 'WARN' when doing this though,
> > > i.e. "I cannot write a proper header to the output file because
> > > it is >4GB".
> > 
> > Maybe something like the attached should be applied? Not sure if
> > this covers all eventualities, still getting acquainted with the
> > source code.
> 
> [...]
> 
> I was about to submit this patch but think I may have detect a logic
> error in existing code.  Thor (or anyone), do you think you could help
> me debug?

I'll try my best.

> Bottom line is if a WAV length of a single chunk is beyond the size
> that can be represented in the 32-bit length field of WAV files then
> issues will occur with certain applications that depend on valid
> lengths.

As far as I can tell, and I am no expert, the problem is that the RIFF
format header should contain the total file size [1] in bytes in the
first chunk header. This will of course be wrong when chunk sizes of
greater than 2**32 are created.

> Some applications understand the basic issue and will go into special
> modes if it see maximum chunk length value of 0xffffffff and thats
> what SoX is attempting to do in these cases.

This is not my experience when creating large wav files with sox, but I
may be doing something wrong. I'll do some further checking.

[...]

> Thor, was there a special reason you used lsx_filelength() instead of
> looking at numSamples with your warning patch?  I ask because file
> length != wav chunk length.

Based on what I read about the header format [2, 3 and others], the
"master" chunk length parameter == file length - first header size -
padding.

> I suspect SoX has some logic error here and is not writing special
> length value of 0xffffffff into header. Code reviews of this area
> appreciated and patches especially welcomed.

This is my experience as well, I'll take a look during the next week.

[...]

[1] Minus header and padding
[2] http://en.wikipedia.org/wiki/WAV
[3] http://www.dragonwins.com/wav/

-- 
best regards
Thor Andreassen