Re: [Hampshire] Editing DVD content?

On 28/01/07, Vic <lug@???> wrote:
> > DVD is a problem. It uses MPEG2. It uses compressions that relies of
> > prediction from previous frames.
>
> MPEG2 uses bidirectional prediction; each GOP may contain the first image
> (I-frame) to be displayed, the last to be displayed (P-frame), and then
> the ones in the middle (B-frames)
> .
> > As such, it is considerably more
> > difficult to edit, because if you try to cut out one of the frames
> > used to predict another frame, the editor has to re-encode the stream.
>
> It has to re-encode the GOP. That's not exactly onerous...
>
> > Generally, editing a MPEG2 stream results is a
> > loss of quality on the output, due to the re-encoding requirement. DV
> > streams do not require any re-encoding so the quality is preserved.
>
> Errr - I don't think you're comparing apples with apples there...
>
> Any time you re-encode video you run the risk of dropping the quality
> because blocking artefact noise becomes general HF noise as soon as you do
> a motion prediction - but that's not what you're seeing. You're seeing the
> difference between a 25Mb/s DV stream with a DVD stream that is generally
> <10Mb/s (often much less). VBR is a Good Thing(tm), but DVD I-frames are
> inevitably bandwidth-limited in the general case...
>
> Vic.
>

I think you missed my point here.
Editing MPEG2 requires re-encoding so quality at the cut/fade/wipe
point results in a degradation of image quality for the GOP containing
the cut/fade/wipe point.
Editing DV does not require re-encoding at all so never looses quality.

Minor point, DVD stream must be <= 10Mbits/s at all times due to the
max read rate of 1x DVD.