What software/hardware dislikes mid-stream QM switching?

[shae]

What software and/or hardware will have issues with switching QMs (mixing MPEG and CQM) in the middle on an AVI?

In addition to switching in general, could it be a problem when a B-VOP using a certain QM is followed by an I-VOP of another?

[Brother John]

Afaik switching matrices violates MPEG-4 specs, so it’s a bad idea to try. Results will be entirely dependent on the decoder implementation, and I’m not aware of any compatibility tests. Why would you want to use different matrices in a movie anyway?

[shae]

I had to do some splicing of streams encoded with different QMs (among other things). It looks fine decoded with ffdshow. I know it's non-spec, but assuming it's easy to implement (which I think would be the case), there's no reason for players not to support it anyway.

[Manao]

It's easy to implement (some decoders will support it without having being designed to, others won't), but from a manufacturer's point of view, there are no reason to implement something that isn't standardized.

[shae]

Implementing a feature the competition doesn't have is something that could set a chip vendor apart. And if it's easy to do so it should be even more lucrative.

Anyway, I'll assume software playback will work okay and hardware might or might not work.

[Ranguvar]

Implementing a feature the competition doesn't have is something that could set a chip vendor apart. And if it's easy to do so it should be even more lucrative.
But I'm guessing less than .1% of the people that ever use that chip will use that feature... files with mid-steam QM switching aren't exactly all over the net, nor are they easy to inadvertently create.