[mythtv] A prelude to transcoding MPEG2->MPEG2
James L. Paul
james at mauibay.net
Mon Dec 8 19:37:39 EST 2003
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On Monday 08 December 2003 13:40, James L. Paul wrote:
> On Monday 08 December 2003 13:17, Derek Atkins wrote:
> > "Geoffrey Hausheer" <ou401cru02 at sneakemail.com> writes:
> > > Note that I have yet to see a PVR250 stream which is DVD compliant.
> > > DVD requires either an AC3 or PCM stream to be present, and I'm not
> > > aware of any way to get such a thing from the PVR250. I've yet to find
> > > an AC3 encoder which is really compliant (the one that comes with
> > > ffmpeg is not compatible with my DVD player, and I've had to use
> > > commercial encoders in Windows to get compliant streams). Anyhow, that
> > > isn't really relevant as it has nothing to do with the issue at hand, I
> > > just thought I'd mention it.
> > Not quite true.. A DVD can also use MP2 audio, which the PVR will do.
> > I was able to make a video DVD without any audio transcoding, and
> > it works just fine in my set-top DVD player.
> I just posted to this effect as well. Here's some specifics on DVD support
> for MPEG audio, from the excellent dvddemystified.com website:
> MPEG audio is multi-channel digital audio, using lossy compression from
> original PCM format with sample rate of 48 kHz at 16 or 20 bits. Both
> MPEG-1 and MPEG-2 formats are supported. The variable bit rate is 32 kbps
> to 912 kbps, with 384 being the normal average rate. MPEG-1 is limited to
> 384 kbps. Channel combinations are (front/surround): 1/0, 2/0, 2/1, 2/2,
> 3/0, 3/1, 3/2, and 5/2. The LFE channel is optional with all combinations.
> The 7.1 channel format adds left-center and right-center channels, but is
> rare for home use. MPEG-2 surround channels are in an extension stream
> matrixed onto the MPEG-1 stereo channels, which makes MPEG-2 audio
> backwards compatible with MPEG-1 hardware (an MPEG-1 system will only see
> the two stereo channels.) MPEG Layer 3 (MP3) and MPEG-2 AAC (also known as
> NBC or unmatrix) are not supported by the DVD-Video standard. MPEG audio is
> not used much on DVDs, although some inexpensive DVD recording software
> programs use MPEG audio, even on NTSC discs, which goes against the DVD
> standard and is not supported by all NTSC players.
Ack.. replying to myself. I just re-read the last sentence above. I took this
to mean that MP3 audio is not supported on DVDs, although it reads as if MPEG
audio in general is not supported on NTSC discs. (Which would contradict all
the info earlier in the paragraph.) It's my understanding that MP2 audio is
supported with the parameters above, although it's admittedly rarely used.
Perhaps somebody here can confirm/clarify this. I'll do more researching when
I get a chance.
FWIW, I have never had one of my DVDs with MP2 audio fail to play in any of
the dozens of standalone players I've tried that can play burned discs. :) So
this is little more than curiosity on my part.
> > > .Geoff
> > -derek
> mythtv-dev mailing list
> mythtv-dev at mythtv.org
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