Re: [SoX-devel] patch to set dwChannelMask to reasonable values

[Chris B. <ch...@cn...>]

On Tue, Jan 4, 2011 at 10:26 PM, David Bryant <da...@wa...> wrote:
> Hi,
>
> A couple times in the past I have received e-mail from WavPack users who
> were having trouble encoding 24-bit wav files written by SoX. The problem
> turned out to be that when SoX creates wav files with the extensible wav
> header it unconditionally sets the dwChannelMask field to zero, which
> implies all channels are unassigned, even in the case of a 1 or 2 channel
> file.
>
> Strictly speaking, this is not a problem for WavPack, but it does mean that
> WavPack will put each channel into its own mono stream (instead of combining
> them into a single stereo stream), and some versions of the WavPack decoder
> (like the one in Rockbox) will not correctly handle multiple-stream WavPack
> files (because they can take more memory to decode).
>
> Setting the channel mask to zero causes problems with other programs as
> well, for example Foobar2000 refuses to play them.
>
> I could not find discussion of this issue anywhere, so I decided to just
> provide a quick patch to set the channel mask to reasonable values for
> common channel counts (1, 2, 4, 6, and 8). It's possible to argue that
> unless the channel configuration is actually known for certain, then a
> channel mask of zero is safest, and it's also true that a real solution
> would allow the channel configuration to pass through SoX from input to
> output. However, I feel that for the overwhelming majority of cases, this
> solution will provide the user with the most usable result.
>

If I recall correctly, 24-bit support was partially driven by
Foobar2000 users liking that format.  So for sure we should try to
accommodate that application.  I do not personally use Foobar2000 so
I'll trust your indication of issue.

I recall talking briefly about topic way back and seemed like sample
applications at the time were OK with but we understood basic issue
could occur.

The patch seems reasonable to me so I'll commit soon.

Perhaps longer term we might have a Ogg-like tag "ChannelMask=0xff".
This is only way sox passes meta data between formats right now (see
vorbis.c and mp3.c) for most part and would allow the channel mask to
be passed from input file to output file... And user can pass in
options using --add-comment syntax.

Thanks again for all the patches!

Chris