Custom matrices and encoding speed

[microchip8]

Hi,

Maybe a silly question, but do custom matrices have an impact on encoding speed?

Thank you.

[Sagittaire]

no ...

[Sharktooth]

uhm... i'd say, yes.
a custom matrix can force the encoder to put more or less bits in certaain or all frequencies rising or lowering the bitrate at a certain quantizer. having a higher bitrate means CABAC will take more time to compress data while a lower bitrate means it will take less.

[Sergey A. Sablin]

uhm... i'd say, yes.
a custom matrix can force the encoder to put more or less bits in certaain or all frequencies rising or lowering the bitrate at a certain quantizer. having a higher bitrate means CABAC will take more time to compress data while a lower bitrate means it will take less.

this only applies to encoding without target bitrate.
for the case you encode to given bitrate using CQM might change encoding analysis, which in turn may affect encoding speed. not that much though as using more advanced ME, RDO...

[microchip8]

mmmkay. So, I'm willing to encode a DVD here with an aspect ratio of 4:3 and I'd like to scale it down from 720x480 to 640x480 and use as bitrate 800 kbps. I'm doing a 2-pass encode. Will the M4G MRM v2 matrix do it? I'd like to keep a balance between blocks and detail. The movie is The Notebook, which doesn't have fast moving action scenes... shall I use the M4G LRM v4 matrix instead of the MRM one?

[Sharktooth]

you should firts try without ANY custom matrix. if it looks good, then keep it.
AVC is not like ASP...

[microchip8]

hmmm, correct me if I'm wrong, but I thought that by using a custom matrix, one could get a higher compression. Sorry for the noob questions, but I'm not really accustomed with matrices :-/

[Sharktooth]

while matrices for ASP were accounting for the quantizer scale limit, on AVC you have a wide range of quantizers and they're also better distributed, so the codec is already pretty good at compressing stuff.
ideally, quant matrices for AVC should have the same balance as the standard flat matrix or they can screw the rate control.
so the question is, why would anyone use a custom matrix with AVC?
the answer is simple: each matrix has it's own purpouse, but usually the standard flat matrix is better.

[microchip8]

okies, i understand. thanks for the answers guys :)