e deleflie <edeleflie at gmail.com> ...> ok, I do realise that the extending the maximum channel count may be > difficult ... there's gotta be a way to do it though.Perhaps a comparison of the FLAC structure with that of Vorbis will help. Within a FLAC stream the audio is split into blocks which are grouped (interleaved). But within each block the eight channels are chained (sequential). This makes sense when there is a maximum of only eight channels. Within a Vorbis stream the audio is split into frames which are grouped (interleaved). Because a Vorbis stream can contain up to 256 channels, within each frame the channels are also grouped (interleaved). So, significantly increasing the number of channels in a FLAC stream is not simple. It would require a second level of grouping (interleaving). In fact, it would require a whole new file format. Regards, Martin -- Martin J Leese E-mail: martin.leese stanfordalumni.org Web: http://members.tripod.com/martin_leese/
Isn't there a standard option to place FLAC data within an Ogg container? I don't use it myself, but I understand that it is quite popular. Would it be possible to interleave multiple FLAC blocks this way? In other words, can Ogg suffice as the second level of grouping that you refer to? Brian Willoughby Sound Consulting On Sep 21, 2009, at 15:04, Martin Leese wrote: e deleflie <edeleflie at gmail.com> ...> ok, I do realise that the extending the maximum channel count may be > difficult ... there's gotta be a way to do it though.Perhaps a comparison of the FLAC structure with that of Vorbis will help. Within a FLAC stream the audio is split into blocks which are grouped (interleaved). But within each block the eight channels are chained (sequential). This makes sense when there is a maximum of only eight channels. Within a Vorbis stream the audio is split into frames which are grouped (interleaved). Because a Vorbis stream can contain up to 256 channels, within each frame the channels are also grouped (interleaved). So, significantly increasing the number of channels in a FLAC stream is not simple. It would require a second level of grouping (interleaving). In fact, it would require a whole new file format. Regards, Martin
I always thought that the best way to put ambisonic media in flac was to use an ogg container, with the 0-order w channel in one flac stream, the three first-order channels in a second flac stream, the five second-order channels in a third flac stream and the seven third-order channels in a forth flac stream. An alternative would be to group the 0-order and first order into the first stream and continue as above for the second and third order channels. Keeping the same-level channels together should help the compression, but different-order channels are likely to have less inter-dependence. Limiting each flac stream to just same-order channels requires four flac streams for a sixteen-channel third-order ambisonic, rather than just two streams, but makes it easier to drop the higher-order channels when desired. Allocation of forth and higher order ambison channels into the flac streams is left open, but higher orders are increasingly difficult to record and therfore are increasingly rare. Forth and higher level may be a purely theoretical concern. -JimC -- James Cloos <cloos at jhcloos.com> OpenPGP: 1024D/ED7DAEA6
On Oct 4, 2009, at 16:48, James Cloos wrote:> I always thought that the best way to put ambisonic media in flac > was to > use an ogg container, with the 0-order w channel in one flac > stream, the > three first-order channels in a second flac stream, the five second- > order > channels in a third flac stream and the seven third-order channels > in a > forth flac stream.Excellent idea!> An alternative would be to group the 0-order and first order into the > first stream and continue as above for the second and third order > channels.This was my first thought, but I did not know how well received the idea would be.> Keeping the same-level channels together should help the compression, > but different-order channels are likely to have less inter-dependence.Very true. I'm not sure how the three (?) first order channels would allow FLAC to take advantage of inter-dependence, because I cannot remember the limits of the current algorithm. Certainly, stereo is analyzed, as are mid-side and a few other variations. I'm just not sure whether any advantage is gained beyond two channels. Archives of this list should have comments from Josh about the current algorithm's capabilities.> Limiting each flac stream to just same-order channels requires four > flac streams for a sixteen-channel third-order ambisonic, rather > than just two streams, but makes it easier to drop the higher-order > channels when desired.Agreed.> Allocation of forth and higher order ambison channels into the flac > streams is left open, but higher orders are increasingly difficult > to record and therfore are increasingly rare. Forth and higher level > may be a purely theoretical concern.This also makes sense. Perhaps you should write up an official recommendation! Brian Willoughby Sound Consulting