For the reasons I can’t disclose I really hate DTS codecs. For those who don’t know there are about three and a half codecs in this family:
- DTS Core
- DTS Core extensions (bitrate extension, two extensions for more channels and an extension for upsampling e.g. 48 kHz -> 96 kHz)
- DTS Lossless (which might depend on core and extend/replace its channels)
- DTS LBR (aka Express profile)
You need to be Jean-Baptiste Kempf to love these formats: DTS Core uses annoyingly large tables, DTS Lossless relies on DTS Core part being decoded properly for it, DTS LBR is a special beast that I’ll describe below. And the best part â€” all those formats are poorly documented (tables are missing for DTS Core, something was missing for DTS Core X96k extension too, bitexact core reconstruction and some other things needed for real lossless decoder implementation are not documented, LBR is not much better either).
So, what makes DTS LBR special? Its coding mode of course. This is a weird codec that employs MDCT (nothing special so far), codes tones separately (that’s not so common) and spreads it all among many chunks for different resolutions that make it “scalable” or whatever.
Nevertheless this post is not about how horrible are all those codecs (if you have ever worked with them it’s obvious and Jean-Baptiste Kempf won’t believe anyway), it’s about obscure relations with other codecs.
When I looked at QDesign Music codec (unsupported by Libav currently) I found that it has suspiciously familiar coding scheme for tones (QDesign Music 1/2 also use tone detection in MDCT frames) â€” I’ve seen it in DTS LBR. And indeed, it seems the same guy created some codec called LBpack that was first to use that approach, then he was employed by QDesign and then by DTS. No wonder it looked similar.
Another piece of trivia â€” there was one guy working on so-called adaptive prediction and transform scheme. Later the prototype known as APT100 was turned into DTS Core. But looks like the same work gave birth to lesser-known codec APT-X (that I’m currently REing but that’s beside the point). And it’s not just the name â€” one codec employs QMF and ADPCM on subbands, another one employs QMF and optional ADPCM on subbands.
All that makes one wonder whether DTS Lossless is related to some lossless codec outside DTS (not necessarily APT Lossless but might be, no details are known about that one). Currently I cannot name any other lossless codec that employs the same coding approach (block coding with different coding for large and small coefficients plus non-adaptive filter). Of course such knowledge won’t change anything but it would be still interesting to know.
P.S. There are rumours that DTS LBR will be made scalable for adaptive streaming, what a fun that will be!
P.P.S. This post was written mainly to test how well new Mike’s setup works.