[FFmpeg-devel] [PATCH] dca: export profile information on decode

[Kostya]

On Mon, Dec 27, 2010 at 06:46:24PM +0200, Anssi Hannula wrote:
> On 27.12.2010 17:41, Kostya wrote:
[...]
> > And mind you, that HD header contains all extensions information coded
> > as flags, though it may be still easier to search for synccodes ;)
> 
> Well, I'd rather use the active extensions bitfield to avoid any false
> positives (as I don't skip the extension payloads as I don't know the
> extension header formats), but I didn't manage to parse it correctly. I
> can take another look, though. Do you have any information about the
> format/location of the active extensions bitmask? (to rule out any
> mistakes on my part)

IIRC, HD block structure is the following:

HD header
1-4 asset headers
asset 1 data
asset 2 data
....

This is all described in DTS-HD decoder substream interface document,
it's proprietary+confidential ^TM but maybe someone can pirately provide
you with a copy. The main PITA is that this information is stored after
mixing info, so you have to parse quite a lot, sometimes in non-trivial
way.

> Hmm, and are those bitmasks provided on a per-asset basis?

Of course. Though it may be missing because there are four asset
types:
0 - ordinary, extension mask present since that's the only case where
it's needed
1 - LBR (low bitrate stuff, I guess nobody cares about it) only
2 - XLL (lossless) only
3 - aux codec (yes, you can put some other codec like AC3 inside HD
    frame this way)

[...]
> > 
> > I meant this flow:
> > 1) determine HD frame position (from core frame length + size checks)
> > 2) if HD is present -> set profile to DTS_HD
> 
> Well there was no DTS_HD profile in the initial proposal. To get the
> distinct DTS_HD types, I guess one should add
> 
> 2.5) search the DTS_HD frame for extensions (or look at the bitmask if
> possible), and upgrade profile accordingly

as you like

> > 3) else do steps 4-5
> > 4) set profile to DTS_CORE
> > 5) search in core frame for XCh and X96 extensions, if found, upgrade
> >    profile to DTS_ES or DTS_96_24
> > 
> > Or, alternatively, you can reuse asset flags system just to signal what
> > extensions are present (0x1 -> core, 0x10 -> core in HD frame,
> > 0x200 -> lossless, etc).
> 
> Yep. As I said above, though, I'd prefer to not make profile a bitfield
> (I consider profiles to be defined collections of settings / encoding
> methods, not a variable that tells every aspect of the bitstream format).

Personally I think there are only two profiles - fully decoded by lavc
and not :) but I recognise other people's needs.
 
> > And let's wait for word from other DTS maintainer.
> 
> Ah, the more opinions the better :)

Opinions based on some knowledge at least.
 
> -- 
> Anssi Hannula