[mythtv-users] PVR250 Settings?

Jarod C. Wilson jcw at wilsonet.com
Thu Feb 12 14:28:04 EST 2004


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On Thursday 12 February 2004 08:07, Jeff wrote:
> Probably because I don't necessarily know what I'm doing. :-)
> I played around a bit and this seems to be ok.
>
> About transcoding though, I'm going from MPEG2 off the PVR250 to
> MPEG4...at least that what I think I'm doing. As far as the bitrate, I
> really didn't know what the bitrate does for the transcoding setting so
> I left it alone. I guessed that since MPEG4 is compressed the bitrate
> setting doesn't mean much on the output file side so perhaps it might
> be limiting the sample rate taken from the input file.
>
> As I said, I'm guessing at a lot of this.

The bitrate setting means a whole lot. Like Derek said, a file captured at 
1331Kbps is going to be 1331Kbps, regardless of encoding type. The end result 
will be files of the exact same size. An mpeg2 capture at 6000Kbps should 
have about the same visual quality of an mpeg4 at 2000Kbps (ymmv).

To make matters worse (in your case), you're tossing out half your lines of 
resolution in that transcode, so you're only preserving half the resolution 
of the mpeg2 capture, but the same bitrate. Effectively, you're using just as 
much space as the mpeg2 capture for an mpeg4 with half the resolution. This 
is a Very Bad Thing (tm).

I'd recommend capturing your mpeg2 stuff at roughly 3x the bitrate of what you 
want the mpeg4 to be. Capture 4500Kbps mpeg2, then transcode down to your 
1331Kbps mpeg4, or something like that. I find it hard to imagine a 352x480 
1331Kbps mpeg2 results in something that is actually bearable to watch...


> At 09:20 AM 2/12/2004 -0600, you wrote:
> >ummm. y?
> >
> >a 1331 bitrate file is going to take up the same amount of space no matter
> >how you encode it.  you're just throwing away cpu cycles transcoding, not
> >to mention quality.
> >
> >Jeff wrote:
> >>>  On Wed, 11 Feb 2004, Matthew Daubenspeck wrote:
> >>> > I finally purchased a PVR250 and got it installed. Let the fun begin!
> >>> >
> >>> > What are other PVR people using for their bitrate settings? I want to
> >>> > find a happy middle between space and quality, and would be
> >>> > interested in finding out what the rest of you think...
> >>
> >>I use 352x480 for a resolution and 1331 (not scaled) for a bitrate.
> >>I transcode these to 352x240 at the same bitrate.


- -- 
Jarod C. Wilson, RHCE

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