[mythtv-users] Resolution

[Joseph A. Caputo]

On Wednesday 03 December 2003 12:34, J. Lucha wrote:
> Ok, I have just been looking over the archives over the last few
> days, and just when I thought I was figuring things out, this thread
> comes along.
>
> I've been using 352x240 MPEG and have been happy with it for TV
> viewing.
>
> But now I want to delve into the archiving aspect with nuvexport, and
> haven't been having much success, I think because of the settings
> I've been using for the capture profile.
>
> When I look at peoples posts regarding nuvexport and doing the same
> things I want to do, I'm totally confused because almost all of them
> have a pvr-250/350 and its hardware encoding.  It appears to be
> easier to do the conversion with the native format produced by this
> card.  But because of my great luck, I'm using software encoding (the
> pvr's came out about 2 1/2 weeks after I bought my capture card).
>
> I'm rambling..
>
> Anyways, what I want to do for the most part is just do what we've
> been doing, and just record and watch shows.  The 352x240 was perfect
> on the TV and such I have.  Now, very rarely, I want to archive a
> recording.
>
> What I've gathered is in NTSC VCD's are at 352x240, SVCD's at
> 480x480, and DVD's are at 720x480.
>
> I tried changing my capture settings to 480x480.  When making SVCD's
> using nuvexport, both my DVD players reject it.  Nuvexport does ask a
> few questions when I select this output format, and so I may be
> answering them incorrectly.

I think there are only 2 likely problems in creating an SVCD (first of 
all, does your DVD player play SVCDs at all?  If you're not sure, try 
downloading a sample SVCD from http://www.vcdhelp.com/).  Assuming your 
player supports SVCD in general, there are still 2 issues.  First, I 
believe what gets created by nuvexport is an XSVCD, or non-standard 
SVCD.  At least, that's what it's telling mpeg2enc to do (it's using 
'-f 5' which is 'user SVCD', as opposed to '-f 4' or 'standard SVCD').  
This may or may not make a difference.  XSVCD allows you to specify a 
bitrate beyond the standard SVCD bitrate (2600 kbit/sec).  So, there 
are 2 things to play with:  try tweaking nuvexport to use '-f 4', and 
make sure your combined audio + video bitrate doesn't exceed 2778 kbit/
sec.  The second issue is that VCD & SVCD audio must be 44100 Hz.  If 
you're recording with a different sample rate, your player may choke.  
On my DVD player, using the wrong sample rate gave me video only; on 
your player it may just choke.  There are 2 possible solutions to this:  
(1) record audio at 44100 Hz.  This may not be possible depending on 
your sound card.  If you're using btaudio, it's likely that you are 
locked in to 32000 Hz, so you'll need option (2) resample the audio.  
The current official version of nuvexport doesn't support resampling, 
but I have a version that does, which I've submitted to the author, who 
I believe has been a bit too busy lately to clean up my changes.  But, 
if you need to resample, I'm attaching my version of nuvexport for you.

> When I use the VCD option of nuvexport, I don't get prompted with any
> question I can screw up :) .  But when I play the created VCD on
> either of my players, it is playing to fast.  Actually, I think the
> video is playing at the proper speed, but the sound is too fast.

This almost certainly sounds like you have an audio sample rate problem.  
See above.

> Since Nuvexport doesn't have a DVD option, I chose to use the DivX
> output to make the AVI file.  I was going to then use one of those
> AVI-->DVD programs, but scratched that when I viewed the AVI file.
> Sound was fine, but the video was very pixelated.
> Again, Nuvexport prompts for some questions that I'm probably
> answering incorrectly.  It prompts for resolution, which I changed
> from the defaults and made them the 480x480 that Myth originally
> captured at.  It also asks for some audio bitrates that I left at the
> default.

If you change the resolution, you need to pump up the video bitrate.  
The default bitrate is OK for 320x240, but for 480x480 (actually, you 
probably want 640x480 or you may get a screwed-up playback aspect 
ration, depending on your player software) you probably want a bitrate 
more in the 2200-3300 range, adjusted to taste.

Hope that helps.

-JAC
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