From: Gert V. <ger...@wx...> - 2001-08-02 17:33:37
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Billy Biggs wrote: > > Gert Vervoort (Ger...@wx...): > > > Attached to this E-mail is a patch of a LPCM audio decoder plugin, to > > get program streams with LPCM working in xine 0.5 (CVS). > > Your code assumes all LPCM streams on a DVD are stereo, 48khz, 16 bit. > My code assumes that too, but I've been told that there's actually a > header which indicates the format and sampling rate. Do you know if > this is documented anywhere? I know there is a header (6 bytes?), which indicates sampling frequency and the number of bits used and such. But, I haven't found any documentation about the meaning of this header. Unfortunatly the MPEG encoder I used to encode my test stream, can only use 2 channels, 16 bits and 48 kHz for LPCM. So, I'm not able to compare streams containing LPCM with different settings to see what changes in the header. > > Here are some sites which indicate to me that we should figure out > this header: > > http://www.disctronics.co.uk/dvd/dvdvideo/dvdv_aud4.htm > http://seneschal.net/papers/dvd.htm > > They both at least seem to think it's more than just 48khz stereo. Are these modes really used in practice? A 2 channel 48 kHz, 16 bit stream already uses a bitrate for the audio of about 1.5 Mbps (total DVD stream 9.8 Mbps max.). If you use multiple channels it can use up to 6.144 Mbps, which leaves little bitrate for the video. This will limit the video quality and also the playing time of the disc. Gert |