[mythtv-users] Pixelation Issues
daspiras at gmail.com
Tue Mar 6 02:32:46 UTC 2007
Thanks for all the feedback guys. Upping the encode rates has seemed
to help. A related question: resolutions and aspect ratios
Currently I record and play at 720x480 but I have to set the aspect
ratio to square in order to have it fill the screen. If I set it to
4:3 there are black bars on each side (and possibly the top, its hard
to tell). This happens even if I record/play in 640x480 as well. If
I don't have it set to square, 4:3 zoom/fill using the W key during
playback works, although it looks worse than set to square. I don't
seem to be losing any of the video when I compare it to what the
direct cable to the tv shows, but I am a little confused as to why 4:3
doesn't work properly?
On 3/5/07, Rod Smith <mythtv at rodsbooks.com> wrote:
> On Monday 05 March 2007 19:21, Brad DerManouelian wrote:
> > On Mar 5, 2007, at 4:18 PM, D wrote:
> > > What are the ideal settings for recording SDtv? I know that it will
> > > differ depending on HW setups, but I feel like I must have something
> > > set up wrong. I've got a pvr-150 encoding to MPEG-PS @ 720x480 at
> > > 2200-2400 kbps and I'm getting pixelation on movement. Should I up the
> > > encoding rate? Should I try a different encoding option such as DVD-2?
> > > What settings do you guys run? What settings would provide the best
> > > possible image?
> My Hauppauge PVR-USB2 is stuck 6000kbps. This seems to be a driver/MythTV
> disconnect concerning the API used to change the encoding rate. At that rate,
> I don't see a lot of pixellation at that rate.
> Many moons ago I had a standalone TiVo, which supported encoding rates that
> ranged from (IIRC) ~1GB/hour to ~4GB/hour. Since 2200kbps is ~1GB/hour, that
> means your setting is equivalent to the standalone TiVo's low-quality
> setting, which may be a useful reference point. Of course, this could be
> comparing apples and oranges, since the encoding hardware may be different.
> It's certainly possible to get much higher quality video at a ~2200kbps rate;
> that's in the neighborhood of what DirecTV and Dish Network use for their
> broadcasts, for instance. These companies, though, use much more expensive
> encoders than a TiVo or a typical MythTV box uses. It's also possible to
> improve the quality by doing multi-pass encoding, but you certainly won't get
> that with on-the-fly encoding from a consumer-grade video encoding card. You
> CAN do multi-pass encoding when transcoding after the fact, though.
> > I run at 640x480 at around 6400 kbps and then transcode down from
> > there to about 4400 kbps if it's something I don't care that much
> > about. I thought 2200 looked pretty awful when I was recording at
> > that bitrate.
> One extra point: When you transcode using MythTV's built-in options, you'll be
> doing one of three things:
> 1) Cutting out sections of the recording without changing the encoding
> method used. This will reduce the file size but shouldn't affect the
> quality of video, except for brief periods around your cut points.
> 2) Converting from whatever encoding method you used to MPEG-4. MPEG-4
> has a reputation for producing higher quality at any given bitrate
> than MPEG-2, so in theory you can reduce the size of an MPEG-2 video
> while retaining most of the quality. (A conversion from one lossy
> format to another WILL degrade the quality slightly, though, even
> if you INCREASE the file size in the process. Hence my use of the
> phrase "most of the quality.")
> 3) Converting from whatever encoding method you use to RTJpeg. This
> encoding method produces larger files than MPEG-4, if you try to
> match the quality. I'm not sure how it compares to MPEG-2. RTJpeg
> consumes less CPU time, though, so it's sometimes used on systems
> with weak CPUs and frame grabber cards. My own experiences with it
> have been pretty negative.
> After encoding with an MPEG-2 card, chances are you'd do #1 or #2, and what
> you (Brad) describe is definitely #2. You might even be able to squeeze a
> 6400 kbps MPEG-2 recording down to less than 4400 kbps without causing too
> much degradation in quality, although of course this is a subjective matter.
> Overall, for long-term storage with an MPEG-2 card, it's probably best to
> encode with a high bitrate (say, 6000-10000 kbps) and then transcode to
> MPEG-4 with a significantly lower bitrate (perhaps 2000-4500 kbps). If you
> expect to watch the show soon, I'd recommend just encoding with a moderate
> bitrate (4000-6000) and then watching it without transcoding it. Of course,
> different people have different ideas of quality, so you should experiment
> yourself. Disk space and CPU speed (for transcoding to a different format)
> can also be important considerations.
> Rod Smith
> mythtv-users mailing list
> mythtv-users at mythtv.org
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