CBR streams and b-frames

[jared1999]

I'm currently involved in a VoD project where we'll be using ASP streams (and maybe H.264). Filesize is not an issue but bitrate, quality and error resilience are. The test encodes are done as 1-pass CBR at 768x576x25 with a maximum I-frame interval of 25, and bitrate at either 2 or 2.5 mbit.

Will I benefit from B-frames in such a scenario? Preliminary tests with two test clips of 2 minutes length show little perceived difference between streams with B-frames and streams with only I- and P-frames.

Also, since B-frames have more than 1 reference, won't they be less error tolerant?

Any other comments regarding encoding for streaming purposes are most welcome.

[Manao]

Bframes actually increase error resilience ( because if they are b0rked, they won't degrade quality of the next frames ), but I'd say it hardly matters.

I'd use bframes, because encoding D1 in CBR at 2 mbits/sec is rather hard, especially when the video gets complicated, and in such case, any bitrate saving here and there is good to take.