Quality-equivalent bitrates between codecs

[Overwind]

Are there any rules of thumb on what bitrates between various codecs will give results of the same quality when transcoding?

For example, if I have a DIVX video encoded at 1300kbps and want to transcode it to H264, what H264 bitrate do I need to use to prevent noticeable quality degradation?

[jagabo]

Use constant quality (or constant quantizer) encoding and you don't have to worry about it. Pick a quality/quantizer you're happy with and encode in a single pass. The codec will use whatever bitrate is necessary (at each frame) to give the quality you specify.

[redwudz]

The only 'rules' I would say exist is that higher compression codecs need less bitrate than lower compression codecs for the same quality. But it would be difficult to make exact comparisons.

H264 = very high compression

WMV and RM and Quicktime fall somewhere in here from high to very high

Xvid & Divx = high compression

MPEG = medium compression

DV = low compression

HuffyUV or similar = very low

If you throw in encoder losses, framesize conversions, available space on the media, audio formats, filtering, source quality, compressibility of the source video, among a few possible variables, it becomes all but impossible to compare formats vs bitrate vs quality with any accuracy, IMO.

[edDV]

One rule of thumb used for true broadcast quality or commercial DVD is VC-1 and H.264 are good for half the bit rate of MPeg2 when encoded from the same high quality source. The goal for MPeg4 AVC codec developement is to push this ratio to 3:1.

A key point is when encoded from the same high quality source. If you encode MPeg4 from an already compressed MPeg2 source, there will be quality loss at half the bit rate.

All this becomes subjective at the user level. Your eyes and monitor may not detect quality loss until much higher compression ratios. Best to test this with your own eyes but remember your next monitor will probably reveal more flaws especially the larger screens.