B-frames

[GonStarTrek]

Are B-frames really neccessary when encoding at high bitrates ? And what would be considered a high bitrate (e.g. 2000kbps or more - or less!). I'm not too bothered about file size. A simple answer would do thanks :D

I've done a search on the forum on this and not really come to a conclusion.:confused:

Ta
GonStarTrek

[jkwarras]

Originally posted by GonStarTrek
I've done a search on the forum on this and not really come to a conclusion.:confused:


B-frames compress some frames more, so it means that you have a loss in terms of quality *but* this bitrate you save on these frames are applied into others frames that will looks better. In fact, the general opinion is that b-frames are very good, and it makes your encode looks better in general, even if some frame swill get more compressed.

For high bitrates an dif you don't care about filesize, then maybe you don't need this extra-compression, as I only do XCD, I don't really know if b-frames are needed for high bitrates encodings.

Regards.

[Bogalvator]

You should always use B-frames!

Just set them at:
Max B-VOP = 2
Ratio = 1
Offset = 0

Then leave the B-VOP sensitivity at 0 (or maybe even lower it, to -10 say)

What is a high bitrate?
Depends on the source: if it's a very high motion film with lots of scene changes then high could be around 6000kbps, but if it's a very dark picture with low motion and not many scene changes then a high bitrate might be 1500kbps.

For your needs it sounds like you should encode at fixed quantizer 2 - this will give constant high quality but can't predict file size.

P.S. Try quant 2 without B-frames and also with the settings above - you probably won't notice ANY difference in quality, but you'll definitely notice the difference in filesize!

[Teegedeck]

Reducing the number of B-frames or not using them at all won't give you anything but a bigger filesize. And if you have to put any limitations on that filesize (like, because you want to burn the result onto CD-R), you'll loose quality by switching them off, not improve it.

Deactivating key features of MPEG-4 ASP won't help the quality of the outcome (and I strongly believe that goes for adaptive quantization, too), IMHO. You could as well go back to simple profile or even use MPEG-2. It doesn't make sense. If you want better quality use the HVS-best matrix (same output-size as MPEG standard) or Andreas78er (for clean sources only) and increase your resolution as much as possible. Switching off B-frames or AQ is something to think about if your encode is saturated, but only then.

[Prettz]

Originally posted by Teegedeck
Reducing the number of B-frames or not using them at all won't give you anything but a bigger filesize. And if you have to put any limitations on that filesize (like, because you want to burn the result onto CD-R), you'll loose quality by switching them off, not improve it.

Deactivating key features of MPEG-4 ASP won't help the quality of the outcome (and I strongly believe that goes for adaptive quantization, too), IMHO. You could as well go back to simple profile or even use MPEG-2. It doesn't make sense. If you want better quality use the HVS-best matrix (same output-size as MPEG standard) or Andreas78er (for clean sources only) and increase your resolution as much as possible. Switching off B-frames or AQ is something to think about if your encode is saturated, but only then.
For doing higher quality encodes, sometimes the higher quantization of b-frames causes unacceptable artifacts in some scenes (for instance, more severe and extremely ugly ringing around objects moving against a smooth-textured background, especially noticeable in animation).

Even in those cases, though, it would still probably be best to use b-frames in your video, but use zones to restrict or disable the use of b-frames in the scenes where the artifacts are most noticeable. Speaking of that, it would be really nice to be able to control more than just the b-frame sensitivity in the zone options...

[Teegedeck]

I cannot say I've ever seen artefacts at that sort of bitrate but that may be because I hardly do animation. Summing it up, nothing beats the good, old MJPEG-encode when it comes to quality. ;)

[JoeShrubbery]

Originally posted by Teegedeck
nothing beats the good, old MJPEG-encode when it comes to quality. ;)

I'd say Huffy personally ^',^