[MPlayer-users] What are b_frames for and should I use them for my mpeg2 encodings(for DVD) ?

[Rich Felker]

On Sun, May 22, 2005 at 09:20:28PM +0100, James Courtier-Dutton wrote:
> On 5/20/05, VJ <vijay.s.gill at gmail.com> wrote:
> > Hi,
> >    As the subjects says, I want to learn what B-frames are, what is
> > their role and will they benefit my mpeg2 encodings which eventually
> > end up on burnt DVD's?
> > 
> > Regards from
> > 
> > VJ
> > 
> 
> I-Frames are encoded frames that can be decoded as a stand alone entity.
> P-Frames (Predicted) use a previous frame and just code motion vectors
> and changes from the previous frame.
> B-Frames (Predicted) use both a previous frame and a following frame to encode.
> I am talking about "previous" and "following" frames in display order.
> They do not appear in the stream in display order.
> 
> So, if you have a scene where not much changes between frames, then
> B-Frames are ideal as they provide the best quality with the minimum
> of space.

This may or may not be true, but does not follow from your reasoning.

> Any rapid action scene is unlikely to benefit from B-Frames.

Unlikely to be true.

> Encoding B-Frames is only possible using a 2-pass process.

Completely false.

> The introduction of B-Frames into a stream results in the Frames in
> stream order not being the same as the display order, so applying
> video editing to streams with B-frames is a lot harder to do than to a
> stream with only I and P frames. In a stream with only I and P frames,
> the stream frame order is the same as the display frame order.

Correct.

Rich