[FFmpeg-devel] [PATCH 1/2] Decode DTS XXCH extension

Nick Brereton nick at nbrereton.net
Sun Jun 24 20:36:12 CEST 2012


The attached patch will decode the DTS XXCH extension giving > 5.1 
channels for DTS-HRA streams. The second patch handling signalling the 
extra channels and their positions.

Note that most 7.1 DTS streams use the XLL (lossless) extension to 
carry the channels, rather than XXCH, so will generally only decode as a 
5.1 core stream.

I also noticed that in the ETSI specification there is a bit called 
FixedBit in the core frame header which is said to always be zero; the 
current decoder takes that bit to indicate the presense of stereo 
downmix coefficients (sets s->downmix) -- presumably DTS changed their 
mind at some-stage as to the meaning of this bit; but if they've decided 
to specify it as always zero does this mean that the option was never 
used? In which case the dca decoder could be cleaned up by removing 
handling for the stereo downmix coefficients?


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