DIVX slow or fast motion?

[egov]

What is the difference between DIVX slow motion and DIVX fast motion?

[Sciascia]

Thay are the same codec, just different encoding algorythms. Most people would think that Fast motion looks better, but the opposite is true. Fast motion uses a hardcoded DRF (Detail reduction filter) of 5x-6x that results in higher compression than taht of slow motin of 2x. The file size of fast motio would be smaller, but lower in quality due to the higher compression level. In 99% of cases it is recommended to use only slow motion as it generally looks better.

Another option is to try using an encoder like NanDub (a version of VirtualDub) that performs multipass and uses both codecs resulting in a much better looking end product. It is a free program and there is an extensive guide and some good forums here. It may look a little daunting at first, but the defaults are pretty good.

[TnT]

Fast Motion will only give better results on heavy action scenes at very low bitrates.

I just use the new http://www.divx.com and the 2-pass VBR.

[Marshmallowman]

I think newer version of divx 4.01, actually switch on the fly(between scenes) between the algorythms (part of mpeg 4 spec).

The lastest DIVx 4.01 has no explicit fast/slow motion setting

[Sciascia]

I haven't played with the newest DivX although it is installed on my machine. The playback quality is better, even for clips encoded with the older 3.11 and Nandub. If it does do multipass and switch between fast and slow automatically, it sounds like the best option. Question is how configurable is it and does it do Scene change detection?

[Aryko]

My naive impression of the difference between the two codecs. Say for example you choose a bitrate of 1500 kbps.

Low-motion operates so that the average bitrate is equal to what you set. So the encoder will try to keep the bitrate at as close to 1500 kbps as possible.

Fast-motion operates so that the maximum bitrate is equal to what you set. So the encoder will try to keep the bitrate beneath 1500 kbps.

At least, that's what I've read, and I've seen smaller file sizes as a result.

- A

[TnT]

Sciascia, it seems to be very configurable since it has options for changing quantizers and such. The scene detection is pretty good, and the key frame setting is actually maximum interval not exact interval. So it'll put in key frames whenever it thinks there is a scene change.

Aryko, I think you are basically correct, but I believe the fast was pretty bad at determining how much it should compress, and usually overdid it.