PCM for H264 ... ???

[Sagittaire]

What is the PCM for H264 codec?
It's usefull for quality?

[Sirber]

never heard of that... :confused:

[Manao]

PCM is a coding mode in which you don't predict the macroblock, you don't transform it, you don't quantize it and you don't compress the coefficients with cabac/cavlc. You just write the values directly, without any encoding, in the bitstream.

Two things though :
- you can't code the value 0 ( so if a pixel is 0, you must write 1 instead )
- it resets the contexts, so it's an error resilience tool, but a pricy one, since you need to write 384 bytes for that macroblock.

It's useless for common encoding - well actually, for pretty much anything.

[akupenguin]

you can't code the value 0 ( so if a pixel is 0, you must write 1 instead )
That only applies to <=main profile. The standard isn't so stupid as to require the use of PCM blocks in certain cases during lossless compression, and then not allow you to losslessly compress with them.