The FLAC format specification never defined the semantics of 7- and 8-channel files, which has caused some pain for some years now. Attached is a patch to define them. I don't know if this follows "follows SMPTE/ITU-R recommendations," but it follows common tool practice. I chose the set of surround speaker designations used by home theatre systems, which is the same set used by the Vorbis and Opus mappings. The ordering follows the WAVE file format, rather than the Vorbis order of other Xiph codecs. This matches what flac has done for the existing mappings, and it allegedly what current tools like libavformat are doing. Please consider applying this patch to have a definitive statement on the channel map for implementors to follow. -r P.S. This doesn't update the flac command-line tool to enforce this mapping. That needs to be done as well, along with test files. -------------- next part --------------
On 09/21/2012 05:22 PM, Ralph Giles wrote:> The FLAC format specification never defined the semantics of 7- and > 8-channel files, which has caused some pain for some years now. > > Attached is a patch to define them. I don't know if this follows > "follows SMPTE/ITU-R recommendations," but it follows common tool > practice. I chose the set of surround speaker designations used by home > theatre systems, which is the same set used by the Vorbis and Opus mappings. > > The ordering follows the WAVE file format, rather than the Vorbis order > of other Xiph codecs. This matches what flac has done for the existing > mappings, and it allegedly what current tools like libavformat are doing. > > Please consider applying this patch to have a definitive statement on > the channel map for implementors to follow. > > -r > > P.S. This doesn't update the flac command-line tool to enforce this > mapping. That needs to be done as well, along with test files.Yes please! I doubt it will stop tool developers from using metadata to define other layouts, but this is a step in the right direction. Thanks, Justin
I like the idea of standardizing the channel maps. I would suggest the following channel orderings: 6.1: L R C LFE Ls Rs Cs (MPEG 6.1 A layout) 7.1: L R C LFE Ls Rs Rls Rrs (MPEG 7.1 B layout) I think this more closely matches what Apple has done and what the default WAVE channel order is (http://msdn.microsoft.com/en-us/windows/hardware/gg463006.aspx). Stephen On Friday, September 21, 2012 at 5:22 PM, Ralph Giles wrote:> The FLAC format specification never defined the semantics of 7- and > 8-channel files, which has caused some pain for some years now. > > Attached is a patch to define them. I don't know if this follows > "follows SMPTE/ITU-R recommendations," but it follows common tool > practice. I chose the set of surround speaker designations used by home > theatre systems, which is the same set used by the Vorbis and Opus mappings. > > The ordering follows the WAVE file format, rather than the Vorbis order > of other Xiph codecs. This matches what flac has done for the existing > mappings, and it allegedly what current tools like libavformat are doing. > > Please consider applying this patch to have a definitive statement on > the channel map for implementors to follow. > > -r > > P.S. This doesn't update the flac command-line tool to enforce this > mapping. That needs to be done as well, along with test files. > > _______________________________________________ > flac-dev mailing list > flac-dev at xiph.org (mailto:flac-dev at xiph.org) > http://lists.xiph.org/mailman/listinfo/flac-dev > > > > > Attachments: > - channel-mapping.patch >-------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.xiph.org/pipermail/flac-dev/attachments/20120921/2f647c0f/attachment.htm
On Fri Sep 21 16:31:21 2012, Stephen F. Booth wrote:> 6.1: L R C LFE Ls Rs Cs (MPEG 6.1 A layout)I'm confused. WAV puts the rear centre before everything but 'Front left of center' and 'Front right of center'. Are you saying you prefer the extra front channels to to side/rear surround, or that you prefer the MPEG order to the WAVE order? -r
Ralph Giles wrote:> The FLAC format specification never defined the semantics of 7- and > 8-channel files, which has caused some pain for some years now. > > Attached is a patch to define them. I don't know if this follows > "follows SMPTE/ITU-R recommendations," but it follows common tool > practice. I chose the set of surround speaker designations used by home > theatre systems, which is the same set used by the Vorbis and Opus mappings.There is some value in having the FLAC mappings be the same as Vorbis and Opus. I've read through this thread and it didn't really come to any conclusion. Can we try again and make a decision this time? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/
On 12-10-12 4:47 AM, Erik de Castro Lopo wrote:> I've read through this thread and it didn't really come to any > conclusion. Can we try again and make a decision this time?Anyone else have thoughts on this? I'd like to get this added before the 1.3.x release. Especially helpful would be research into what current tools actually do. -r