Re: QDMC progress, updated

Sascha Sommer wrote:

>>I once dug into Quicktime.qts and mapped out (what I think was)
>>the call tree for the QDM* decoder (apparently, QDMC and QDM2 are handled
>>by the same section of code). It was big; no, huge. Conceptually, it might
>>    
>>
>
>Just curious, but do you remember the version of this Quicktime.qts?
>Nowadays (QT5/6) the QDMC decoding function seems to be in
>QickTimeInternetExtras.qtx while the QDM2 decoder can be found in
>Quicktime.qts.
>
>Sascha
>  
>
Hmm, I was guessing that the codecs where the same but with slightly 
different bitstream. And I remembered checking the qt 3 dll. And in 
there I found a qdm2decompressor, abit strange when qdm2 was introduced 
in qt4. (http://www.oldversion.com for old quicktime versions.)

My guess is that the original bitstream header wasn't designed for 
streaming, so they just redid the header.  I don't have so many qdmc 
samples to analyse. But this is what I've found out so far about the 
qdmc1 header structure. (Analysing with 2 samples.)

B1 B2 B3 B4 B5    B6 B7 B8 B9 B10 BXX
Q  M  C  01 Checksum 59 48 B2 90  DATA

The checksum routine is the same as in qdm2 but with other bytes and 
swapped order. (Attached is a matlab routine for calculating the checksum).

For every compressedpacket to include QMC is by me not needed. So if one 
would need to know the length of the whole packet by just looking at the 
header just remove the QMD and replace it with something useful(as it is 
in qdm2).

If anybody has software for generating QDM1 files I would be intrested 
in that.

/Benjamin