[MEncoder-users] How important are B-frames?

[James Hastings-Trew]

On 12-05-03 9:23 PM, Sylvester 4 wrote:
> How important are B-frames and does a video really need them?
>
> "MEncoder's libavformat muxing is presently broken and can generate
> INCORRECT files in the presence of B-frames. Moreover, due to bugs MPlayer
> will play these INCORRECT files as if nothing were wrong!"
>
> If I encode using -of lavf, the above is displayed.  So, I would set
> bframes=0 thinking this must be the correct procedure.  But I am now
> wondering if a video is suffering in quality due to zero B-frames in
> the video.
>
> Also, in MPEG-2 files, I notice they have - 99% of the time - BVOP.  I
> think I remember it stands for bidirectional video object plane.  Is
> this just another name for B-frames?
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B-frames allow for a greater amount of compression because they 
represent a diff from both following frames and previous frames, in both 
temporal directions. Therefore they are not essential, and basically for 
years I used mencoder to create mp4 files with zero b-frames with no ill 
visual effect. Just slightly larger files. I should also note that some 
devices with very small frame buffers cannot handle video streams with 
b-frames correctly anyway - the original appleTV comes to mind, as well 
as many portable devices. The presence of b-frames requires buffering 
x-number of frames because b-frames can be delivered out of stream order 
and must be buffered at playback time.