When to use rate-distortion algorithm (slow/slowest mode)?

[w2e3r4]

Hello,

To quote divx guide
"rate-distortion algorithm is designed to dramatically improve video quality at low bitrates". At what bitrates it makes sense to turn it on, provided that it increases encoding time like 3 times?

Thanks,

[seewen]

"Bitrate" means nothing alone.

A bitrate of 500kbits. It's high or low bitrate ?

If your clip has a resolution of 32x32, and represent a white square inside a black one (without any motion)... The bitrate is really "high".

If your clip is the movie Matrix, with a resolution of 720x304, this very same bitrate is really "low".
--

You should try to encode a movie, in "standard" mode. Use "1 pass quality-based" with Quantizer = 2 (= 97%). Don't forget to check "Write log file" (and B-frame if you want B-frame, etc..).

At then end, you have an *.avi of (say) 1000Mo. After that, you can run a "second pass" (use the log file of the 1st pass, of course).

If you aim a target size which is 80-100% size of the 1st pass *.avi, you can say that it's "high bitrate".
Between 60-70%, it's "medium bitrate".
Under 50% it's "low bitrtate".

So if you want a target size of 400Mo (beccause you want a final *.avi of 700Mo, and you have an audio of 300Mo), you aim for 40% of the original size, which is a really "low bitrate".

[DevilsChild]

I wouldn't use Slow or Slowest modes unless you have a really low bits/pixel. Standard in 3 passes gives acceptable quality for all my encodes.