Mailing List Archive

On Tue, 2003-05-20 at 13:20, Vinton Coffman wrote:
> Can someone post their capture settings for the PVR-250
> frame size
> video quality ?%
> audio rate kb/s
> file size

The only setting for the PVR-250 that Myth can configure is the
resolution (at least as far as I know). I noticed a slight bit of
ghosting when capturing at 480x480, but that went away when I switched
to 720x480.

Joe

At 02:20 PM 5/20/2003 -0400, you wrote:
>I see ghosting on my pvr-250 too. Not real noticeable to watch, but I'm
>sure its contributing to the large file size. I'm not using the best
>cables but I saw some other people mention ghosting. Has anyone used
>their pvr-250 card under Windows in the same setup and NOT seen the
>ghosting. I can't try it myself since I don't have Windows. This would
>indicate its the ivtv driver rather than defective hardware or bad cabling.

Hi Vinton, I'm using a 250 and am not seeing any ghosting in Linux or in
Windows. Good quality cables as directly connected to the feed in to the
house as possible.

-Jeff

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As I think I've posted before, I'm using custom profiles that are
hardcoded for the PVR-250 to differentiate them from the standard
profiles I use for my Bt8x8 cards. The ghost issue you're seeing is
related to the ivtv driver where the capture resolution isn't
720x480.

The sound is hardcoded for 384Kbps, so the audio quality that you put
in the setup is ignored.

The 16Mbps is a maximum; the average (if you do your math) is
probably going to come out closer to 8Mbps.

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I switched the frame size to 720x480 and that did take care of the
ghosts. I bought some better cables too.

I set the video quality to 50% but that doesn't seem to effect the bit
rate. Mythbackend now reports
Stream #0.0: Video: mpegvideo, 720x480, 29.97 fps, 16000 kb/s
Stream #0.1: Audio: mp2, 48000 Hz, stero, 384 kb/s

Now the average file size is ~3.8 GB/hour.

Can someone post their settings or the procedure necessary to reduce
the bit rate. I was under the impression that people were getting
about 2 GB/h with the pvr-250. Can anyone with a 250 card verify this.

BTW, I hooked my GeForce 4 440MX card up to a sony 20" tonight using a
really good s-video cable. The picture detail is nice but the color is
a little flat compared to the same recording viewed on a 17" Apple
monitor. I haven't mucked with the XF86Config file yet. I still need
to set up the over scanning. I was running at 1024x768. I'm going to
try 800x600 and see if the color brightens up any and if the mythtv
menus are any more readable. Just a little on the fuzzy side. I seem
to remember reading something about changing a line in the code to
enable better font rendering.

TIA

On Tuesday 20 May 2003 10:46 pm, Vinton Coffman wrote:
> I switched the frame size to 720x480 and that did take care of the
> ghosts. I bought some better cables too.
>
> I set the video quality to 50% but that doesn't seem to effect the bit
> rate. Mythbackend now reports
> Stream #0.0: Video: mpegvideo, 720x480, 29.97 fps, 16000 kb/s
> Stream #0.1: Audio: mp2, 48000 Hz, stero, 384 kb/s
>
> Now the average file size is ~3.8 GB/hour.
>
> Can someone post their settings or the procedure necessary to reduce
> the bit rate. I was under the impression that people were getting
> about 2 GB/h with the pvr-250. Can anyone with a 250 card verify this.

Everyone that's mentioned the default bitrate of the wintv-pvr cards has said
it's set to VBR 8000 kbps (4GB/hour). You're the only one that's (wrongly)
said that they're 2GB/hour at the default bitrate.

There's stuff in the ivtv driver now to change the bitrate, but it's going to
be changing sometime so it's not really worthwhile to support it yet.

Isaac

For what it's worth since no one actually answered Vinton's question, this is the relavant piece of ivtv-api.c:

/* Initial settings */
itv->v4l2.codec.bitrate = 8000000;
itv->v4l2.codec.bitrate_peak = 16000000;
itv->v4l2.codec.stream_type = IVTV_STREAM_PS;

Change the bitrate to 4M and the bitrate_peak to 8M and recompile for roughly 2G/hr file sizes.

-----Original Message-----
From: Isaac Richards [mailto:ijr@po.cwru.edu]
Sent: Tuesday, May 20, 2003 9:25 PM
To: Discussion about mythtv
Subject: Re: [mythtv-users] RE:prv-250 capture settings and video
quality


On Tuesday 20 May 2003 10:46 pm, Vinton Coffman wrote:
> I switched the frame size to 720x480 and that did take care of the
> ghosts. I bought some better cables too.
>
> I set the video quality to 50% but that doesn't seem to effect the bit
> rate. Mythbackend now reports
> Stream #0.0: Video: mpegvideo, 720x480, 29.97 fps, 16000 kb/s
> Stream #0.1: Audio: mp2, 48000 Hz, stero, 384 kb/s
>
> Now the average file size is ~3.8 GB/hour.
>
> Can someone post their settings or the procedure necessary to reduce
> the bit rate. I was under the impression that people were getting
> about 2 GB/h with the pvr-250. Can anyone with a 250 card verify this.

Everyone that's mentioned the default bitrate of the wintv-pvr cards has said
it's set to VBR 8000 kbps (4GB/hour). You're the only one that's (wrongly)
said that they're 2GB/hour at the default bitrate.

There's stuff in the ivtv driver now to change the bitrate, but it's going to
be changing sometime so it's not really worthwhile to support it yet.

Isaac
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On Tuesday 20 May 2003 10:46 pm, Vinton Coffman wrote:
> Now the average file size is ~3.8 GB/hour.
>
> Can someone post their settings or the procedure necessary to reduce
> the bit rate. I was under the impression that people were getting
> about 2 GB/h with the pvr-250. Can anyone with a 250 card verify
this.

Another option is to add the following to one of your system init
scripts:

/path/to/ivtv/utils/test_ioctl -c bitrate=2500000,bitrate_peak=8000000

On my system, this reduced the file size for a 576x480 recording from
4.3 Gb/hr to 1.6 Gb per hour.

p.

Jason, thanks for answering my question. I plan to try it tonight. Is
there a formula or spec for choosing bitrate and peak bitrate? Is peak
always 2x the base bitrate?

> > Can someone post their settings or the procedure necessary to reduce
> > the bit rate. I was under the impression that people were getting
> > about 2 GB/h with the pvr-250. Can anyone with a 250 card verify
this.

> Everyone that's mentioned the default bitrate of the wintv-pvr cards
has said
> it's set to VBR 8000 kbps (4GB/hour). You're the only one that's
(wrongly)
> said that they're 2GB/hour at the default bitrate.

> There's stuff in the ivtv driver now to change the bitrate, but it's
going to
> be changing sometime so it's not really worthwhile to support it yet.
>
> Isaac

As for being the only one "wrongly" saying 2GB/hour, I read this before
I started using the project when I was still spec'ing the hardware I
wanted to buy. It's from a HOW-TO draft that was being circulated on
this list. I didn't know that it didn't apply to the pvr-250 and I was
asking for confirmation, not stating a fact.

> 3.3.3 Hard Disk(s)
>
> Encoded video takes up a lot of hard disk space. The exact amount
depends
> on the encoding scheme, the size of the raw images, and the frames per
> second, but a typical value for MythTV is 2 GB/hour. Allow enough
space.

FWIW, the box the pvr-250 plainly states on the left end of the box
"Hardware MPEG-2 video and audio encoder, so you only need 1-2
Gigabytes per hour of recorded video."

Moving on, I want to thank Isaac and company for a great piece of
software.

I just read an article on excite that future versions of ReplayTV will
possibly lose their ability to automatically skip commercials. This
happens to be the major "Wow!" feature when I show people MythTV.

BTW, I would be willing to build, maintain, and host a FAQ page
compiling info on using the pvr-250 with MythTV. Presently, it seems
one has to dig through the list archives or cvs repository to find
basic info. I would like to give back to the project and thought this
might be a useful source for people new to the project wanting to use
this card.

Let me know if I should move forward with this idea. It would need a
link on the MythTV site to be useful.

Thanks,
Vinton