Mailing List Archive

> Since all of the compression is done on the G200 card,
> the speed of CPU shouldn't matter much. CPU
> utilization with the G200 during
> compression/decompression was usually only 3-4 percent
> using MJPEG and decimation 2. The G200 drops frames if
> you increase the decimation to d 1 (640x480).
>
> I put a WinTV card in when I took the G200 out.
>
> ./jj


So, why did you put in a WinTV card instead of just switching compression
codecs?

I figured I'd order up a fast new Athlon mb, and either use the G200 with hw
mjpeg and decimation 1 (which you say doesn't work) or go to Mpeg4. Are you
saying that won't work?

Thanks,
JC

--- JC <johnmythtv@crombe.com> wrote:
> So, why did you put in a WinTV card instead of just
> switching compression
> codecs?
>
> I figured I'd order up a fast new Athlon mb, and
> either use the G200 with hw
> mjpeg and decimation 1 (which you say doesn't work)
> or go to Mpeg4. Are you
> saying that won't work?

It won't work any better than your current setup. You
can't get decimation 1 with the G200 without dropping
a lot of frames. For more information, see the mailing
lists at marvel.sourceforge.net.

I replaced the G200 TV with a WinTV for two reasons:
higher resolution and wanting it to "just work."

I did this before 0.8 came out, and getting the G200
working sounded pretty hairy. There appeared to be
more problems than success stories on this list with
the G200, and my initial attempts to get it working
under Myth didn't work. At this point, I might try
reinstalling it and see if I can get it working.

After much frustration, I decided to go with new
hardware that was well-understood and worked well for
a lot of people.

Of course, at this point, I'm having image quality,
stability, and CPU utilization problems with the WinTV
based setup, so I may put the G200 back in even though
I'll have lower resolution.

./jj

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I also have problems with CPU load in the areas you mentioned. I'm running
Myth on a 1600x1200 X display; XP 2000, 64meg GeForce3 Ultra DDR (pre-Ti).

I can't run MPEG4 at anything approaching a reasonable quality level, but
RTjpeg at 720x480 is perfectly fine for recording and playing. From your
testing, it sounds like I would be fine if I dropped the resolution and
colordepth.

FWIW, if this turns out to be partially the fault of the most recent nVidia
drivers, version 1.0.3123 is still available from Gentoo...

Thanks for the legwork,


#if Jason James /* Mar 20, 19:39 */
> To test my video performance, I ran glxgears. I got a slow 418
> FPS. Turning ACPI off in the kernel improved performance to about 520
> FPS. I got it up to 1200 FPS by switching from 24 bit to 16 bit graphics.
#endif /* jason_james_97@yahoo.com */

Andy Davidoff wrote:
> I also have problems with CPU load in the areas you mentioned. I'm running
> Myth on a 1600x1200 X display; XP 2000, 64meg GeForce3 Ultra DDR (pre-Ti).
>
> I can't run MPEG4 at anything approaching a reasonable quality level, but
> RTjpeg at 720x480 is perfectly fine for recording and playing. From your
> testing, it sounds like I would be fine if I dropped the resolution and
> colordepth.
>

There are a lot of people searching for the magic setup to get good
quality w/o using up a lot of the processor. I had a real hard time
with this also for a while, because I started with the assumption that
the Myth defaults for MP4 quality were correct and that I just needed to
turn up the resolution. This is very wrong (at least for me)

I've found that it works much better to turn down the resolution and
cracking up the MP4 min quality.

Try:

Resolution to 480x480
MP4 Min Quality = 4
Max Quality = 1
Max Diff = 2

See what happens. I think you will be happy. I'm getting a great
picture and only using like 50% of my Athlon XP1700.

Also, if it helps, my understanding of MP4 settings:
Resolution - by far the biggest factor in determining the amount of
processing power. Increasing this increases processor requirement by a
factor of 4.
Bitrate - lowering this will reduce quality by dropping data, therefore
no affect on processor power, but will affect disk space.
Max/Min Quality - lowering this will improve quality by using more
compression and more processor power. I haven't seen swing of more then
10% changing from the default quality settings and max settings.

If anyone else has a better understanding, please correct me.

-rac

Ryan A. Carris wrote:
...
> Also, if it helps, my understanding of MP4 settings:
> Resolution - by far the biggest factor in determining the amount of
> processing power. Increasing this increases processor requirement by a
> factor of 4.
> Bitrate - lowering this will reduce quality by dropping data, therefore
> no affect on processor power, but will affect disk space.
> Max/Min Quality - lowering this will improve quality by using more
> compression and more processor power. I haven't seen swing of more then
> 10% changing from the default quality settings and max settings.

So if I drop the bit rate to zero and set the quality to all
1s I'd get perfect recordings that take up no disk space? ;-)

To get fewer artifacts, you need more information which
means a higher bit rate. The Quality factors are artificial
limits to mark when to do something desperate. They don't
add more information to the stream. In fact, you can cause
encoding to go screwy if they are too far out of line.

If the bit rate is low, the encoder saves space by making
blocks instead of tracking each individual pixel. Therefore,
you can usually get more unique information on screen by
raising the bit rate rather than raising the resolution. And,
as you point out, raising the bit rate has less impact on the
CPU (but will use up more disk space).

Broadcast NTSC or PAL is crappy. Resolutions beyond a width
of 480 just give a more perfect reproduction of the crappy
picture. I believe this is why the commercial products use
widths from 352 thru 544. Higher widths are a waste of disk
space for no real perceivable quality improvement.

So, my favorite setup right now is 544x480, 4400 scaled bit
rate. This only use ~60% CPU time on a 1.3GHz Duron. A bit
rate of 5500 can look a little better for lots of motion but
not enough better to justify wasting more disk space. I record
lots of basketball games and it still looks okay despite the
motion. The T... commercial product attached to the same TV
has much more noticeable artifacts during basketball games.

-- bjm

> Broadcast NTSC or PAL is crappy. Resolutions beyond a width
> of 480 just give a more perfect reproduction of the crappy
> picture. I believe this is why the commercial products use
> widths from 352 thru 544. Higher widths are a waste of disk
> space for no real perceivable quality improvement.

I know that's the theory of broadcast NTSC/PAL signals, and I know it's
also the reality that anything over 480 is overkill. But I've found that
on my setup (BT878 card), using MP4, I get a better image by capturing at
720 horizontal. Everything in the image seems a lot sharper to me.

I don't know why--maybe some quirk with the BT878 driver, something with
the nuppel codecs, maybe even something weird with my video card (G400)
scaling the output to fullscreen during playback. I know it shouldn't be
that way, but that's just what I've observed on my system.

[.disclaimer: I haven't switched from 720 to a lower res for several
months, so it's possible it was just something in a previous CVS that was
squirrely which produced what I was seeing.]



>
> So, my favorite setup right now is 544x480, 4400 scaled bit
> rate. This only use ~60% CPU time on a 1.3GHz Duron. A bit
> rate of 5500 can look a little better for lots of motion but
> not enough better to justify wasting more disk space. I record
> lots of basketball games and it still looks okay despite the
> motion. The T... commercial product attached to the same TV
> has much more noticeable artifacts during basketball games.
>
> -- bjm
>
>
>
>
> _______________________________________________
> mythtv-users mailing list
> mythtv-users@snowman.net
> http://lists.snowman.net/cgi-bin/mailman/listinfo/mythtv-users

William Preston wrote:
>>Broadcast NTSC or PAL is crappy. Resolutions beyond a width
>>of 480 just give a more perfect reproduction of the crappy
>>picture. I believe this is why the commercial products use
>>widths from 352 thru 544. Higher widths are a waste of disk
>>space for no real perceivable quality improvement.
>
>
> I know that's the theory of broadcast NTSC/PAL signals, and I know it's
> also the reality that anything over 480 is overkill. But I've found that
> on my setup (BT878 card), using MP4, I get a better image by capturing at
> 720 horizontal. Everything in the image seems a lot sharper to me.

Yes, it is going to be better. The question is if it is enough
better to justify using the resources. If the files are
twice as big, would someone prefer a slightly better picture
or twice as much recording time. Since the commercial products
advertise their recording capacity, they tend to stick to
'good enough' resolution.

Also, if I connect a DVD player directly into the S-Video input
of a capture card, higher resolutions up to 720 are obviously
clearer. With coax cable, the law of diminishing returns rules
and I don't know if I could distinguish 640 from 544 in a taste
test.

-- bjm

> > I know that's the theory of broadcast NTSC/PAL signals, and I know it's
> > also the reality that anything over 480 is overkill. But I've found
that
> > on my setup (BT878 card), using MP4, I get a better image by capturing
at
> > 720 horizontal. Everything in the image seems a lot sharper to me.
>
> Yes, it is going to be better. The question is if it is enough
> better to justify using the resources. If the files are
> twice as big, would someone prefer a slightly better picture
> or twice as much recording time. Since the commercial products
> advertise their recording capacity, they tend to stick to
> 'good enough' resolution.

I'm seeing the same thing on my PAL setup. Using horizontal at 480 has a
lot of very visible artifacts and other cruft. It is like looking at a tv
with bad reception, wavy lines, etc. Raising to about 576 makes a dramatic
improvement in quality and going onwards to 720/768 gives a further
reasonable improvement in quality.

Curiously dropping horizonal res to less than 576 does not drop quality very
quickly. I might have expected artifacts due to the way the de-interlacer
works to start creeping in...? Currently 576x576 is what I am finding I
need for a high quality TV picture, I would like to go with more width but
the pc is not big enough I think (dual CPU 933Mhz intel - I think that Myth
does not take advantage of extra CPU's when encoding?)

Perhaps this is not so visible with NTSC, or perhaps it is just a feature of
whatever BT8xx chipset myself and William have (I have a leadtek 2000 XP)?