I vote for documenting the --channel-map option in the --help I don't like the idea of rejecting a multichannel file merely for mapping, so there should be a documented option plus an error message pointing to the option. This should compare to the WAVE and AIFF errors where the utility suggests to the user how to get the file converted safely. Brian Willoughby Sound Consulting On Jan 17, 2013, at 17:34, Ralph Giles wrote:> On 13-01-01 4:36 PM, Tim W. wrote: >> - 4 channels: left, right, back left, back right (FL FR BL BR) >> - 5 channels: left, right, center, back/surround left, back/ >> surround right >> (FL FR FC BL BR or FL FR FC SL SR, same order so >> doesn't matter) >> - 6 channels: left, right, center, LFE, back/surround left, back/ >> surround right >> (FL FR FC LFE BL BR or FL FR FC LFE SL SR, same >> order so doesn't matter) > > I looked at the 'flac' command-line front-end code today, and it uses > Back Left and Back Right for 4 channel but Side Left and Side Right > for > 5 and 6 channel files when writing out WAVE from FLAC files without a > WAVFORMATEXTENSIBLE_CHANNEL_MASK metadata tag. > > As you say, the order is the same, and for less that 7 channels the > physical speaker configurations are equivalent. > > The encoder accepts both Side and Back in the input channel mask, but > passes them on in the tag, of course. If the input is AIFF the support > is more limited, rejecting any multichannel file unless the > undocumented > --channel-map=none is passed, followed by some dead code saying > only 1, > 2, 3, and 5 channels can be unambiguously mapped. > >> - 6.1: FL FR FC LFE BC SL SR (L R C LFE Cs Ls Rs) >> - 7.1: FL FR FC LFE BL BR SL SR (L R C LFE Rls Rrs Ls Rs) > > Again, I'm suggesting we update the spec to define these as the > default > channel maps for 7 and 8 channel FLAC files in the absence of the > overriding WAVFORMATEXTENSIBLE_CHANNEL_MASK metadata tag, and > modify the > included 'flac' front-end to write out those masks when decoding such > files. Likewise, we would modify 'flac' to accept files with those > channel masks as input when encoding. > > Untested patch attached.
On 13-01-17 7:26 PM, Brian Willoughby wrote:> I vote for documenting the --channel-map option in the --helpI suspect it's undocumented because 'none' is the only implemented argument, which is a way to work around the defined channel map signalling. I.e. it doesn't make interoperable files. -r
On 13-01-17 7:26 PM, Brian Willoughby wrote:> I vote for documenting the --channel-map option in the --helpDo you ever use --channel-map yourself, or recommend it to clients? -r
On Jan 17, 2013, at 21:41, Ralph Giles wrote:> On 13-01-17 7:26 PM, Brian Willoughby wrote: >> I vote for documenting the --channel-map option in the --help > > Do you ever use --channel-map yourself, or recommend it to clients?Professional surround mastering is delivered on very specific media, and FLAC is not an option (to my knowledge). I use FLAC for archival of original recordings, and I document the channel order along with the other details of the recording. I recommend the same practice to anyone. FLAC works best with mono and stereo. Only stereo can take advantage of compression options that share channels. More than two channels in a FLAC does not really offer any space savings beyond what you would get with multiple mono FLAC files. But if you do archive 8-channels recordings, you'd be well advised to document more than just the channel mapping. Actually, there's quite a large world of possibilities. There are recording devices, archival methods, media exchange standards for mastering, and only after all of those stages is there delivery to the consumer. I'm not aware of any surround material being delivered in FLAC yet, neither to mastering houses or consumers. It seems that surround is mostly limited to Dolby Digital, DTS, and is limited to DVD and BD (Blu-ray Disc). I have seen some new things popping up, but many of them look really ugly in one aspect or another. Are you aware of FLAC being used apart from recording devices (1 to 8 channels), archival (multiple mono and stereo), computer audio, or consumer stereo audio? It seems that there are two areas where surround FLAC could take off (mastering formats and consumer media). Brian