Re: debconf5 - videos of the talks and BOFs available
[Cross-posted to debconf5-video now that I'm subscribed to it; perhaps
this should move away from debconf5-event.]
On Mon, 2005-07-25 at 13:16 +0200, Herman Robak wrote:
> On Mon, 2005-07-25 at 11:25 +0100, Ben Hutchings wrote:
> > Herman Robak wrote:
> >
> > > Does this process involve recoding, or can vanilla DVD players
> > > handle the non-constrained MPEG1 streams that we have published?
> >
> > I originally hoped to be able to use the MPEG1 streams unaltered, so
> > that the DVD could be distributed as a jigdo, but I have now resorted
> > to using mencoder to recode into MPEG2 and scale to full size at the
> > same time.
>
> Recoding back to a higher resolution is a no-no, when avoidable.
Is it avoidable? I suppose it would be possible to scale down to
352x288/240, but I wonder how that would look.
> > > We still have most of the raw material, and John has the rest in
> > > high quality full resolution XviD. Recoding from that would yield
> > > more pleasant results.
> >
> > Yes - though they would also be much larger. I'm getting everything
> > onto two single-layer or one dual-layer disc by recoding to roughly
> > the same bit rate as the source files from dc5video.
>
> You could encode from the original sources with the same bitrate,
> but that would probably result in a lot of ugly artifacts. 400 kbit/s
> is not a reasonable bitrate for 720x576 video using MPEG2.
Well, I'm still using MPEG2 in my second attempt. It is not difficult
to change the encoding parameters; there's just a long wait afterwards!
> If I recall
> correctly, DVD players can handle 352x288, too. I don't remember what
> the exact constraints were on the audio. I suspect 32 KHz is out of
> spec, and that 44.1 KHz is required.
I believe only 48 kHz MP2 is allowed (which is odd, because DVD players
are required to play CDs too). So I'm resampling at 48 kHz in my second
attempt. For a compliant "NTSC" disc the audio track needs to be AC3
(or LPCM, but that would be silly).
> > > And a 48 frames GOP is way beyond the 12-15 of VCD and DVD.
> >
> > Assuming that the GOP length is the same as what mencoder calls
> > "keyframe interval", it claims the maximum is 132,
>
> I think the maximum for unconstrained MPEG is even higher,
> but you can't expect that to work on a standalone DVD player!
The mencoder manual page says that "[f]or a strict MPEG-1/2/4 compliance
this would have to be <=132."
> > so that's what I selected when recording. Which would explain
> > why seeking doesn't work very well on my test discs... So I'll
> > fix that.
>
> If you want to be sure that the video is playable on all DVD
> players, the GOP should not be larger than 12 for PAL and 15 for
> NTSC.
The Wikipedia page <http://en.wikipedia.org/wiki/MPEG-2#MPEG-2_on_DVD>
says 15 and 18 respectively. Where do you get those lower figures from?
> This is less efficient for low-motion content like these
> conference recordings. However, it is prudent to make sure that
> the DVD plays without a hitch even on the most inept players.
Right.
Ben.
--
Ben Hutchings
Unix is many things to many people,
but it's never been everything to anybody.
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