[mythtv-users] How to improve capture quality

Jay Mallar jaymallar at gmail.com
Mon Oct 22 19:56:37 UTC 2007


Jay Mallar wrote:
> Steve Peters - Priority Electronics wrote:
>> What is your recording bitrate set at?
>>
>>     -----Original Message-----
>>     *From:* mythtv-users-bounces at mythtv.org
>>     [mailto:mythtv-users-bounces at mythtv.org] *On Behalf Of *Jay Mallar
>>     *Sent:* Monday, October 22, 2007 9:46 AM
>>     *To:* Discussion about mythtv
>>     *Subject:* [mythtv-users] How to improve capture quality
>>
>>     My machine:
>>
>>     Intel Quad Core (Q6600)
>>     Asus P5N32-Plus MB
>>     EVGA GeForce 6200-LE
>>     Hauppauge PVR-250
>>
>>     My video card is connected to my monitor via the VGA port and to
>>     my TV.   The TV connection is S-video out to an RF Modulator to
>>     my TV's cable input.
>>
>>     The quality of video captured via the PVR-250 isn't what I'd
>>     hoped for.  I thought at first that the video card or the
>>     connection to my TV had been the problem, but that isn't the
>>     case.  I've watched DVDs and AVIs on the machine via the same
>>     video connection to my TV and the images are sharp and clean.
>>
>>     However when I capture video and replay it, it is grainy at
>>     best.  When the image changes rapidly, I get what I can only hope
>>     to describe as problems with refresh timing; I see this big
>>     horizontal lines where it looks like the image was painted to a
>>     certain point and then repainted again before it finished.  It's
>>     worse with high-contrast, fast action.
>>
>>     I suspect I need to tweak the capture settings, but I'm curious
>>     what the best values are.  I tried using the settings from the
>>     Wiki (http://www.mythtv.org/wiki/index.php/Recording_Parameters),
>>     but those don't seem to be getting me where I'd hoped to be. 
>>
>>     At the very least, shouldn't I be able to get the quality I see
>>     when I hook my TV directly to the satellite STB or to the output
>>     from my TiVo  (Are these TiVo values accurate? 
>>     http://alfter.us/tivo2svcd.shtml?)
>>
>>     Setting the resolution to anything higher than width of 480 seems
>>     to have no effect.    Myth won't let me change height above 480. 
>>     I got a bit lost the settings for bitrate etc..    Not sure if
>>     bitrate is avg or min or both, and not sure if Myth uses VBR or
>>     CBR.  From what I've read avg bitrate should be set below max
>>     bitrate, but I'm not getting good results trying to tweak on my own.
>>
>> ------------------------------------------------------------------------
>>
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>> mythtv-users at mythtv.org
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>>   
> Right now It's set to 480x480, MPEG-2 PS, 4:3, BR 5800, MBR 8000, but 
> I've also used the defaults of 480x480, MPEG-2 PS, 4:3, BR 4500, MBR 
> 6000 as well and honestly can't tell the difference between them.
>
Here's some examples of the quality problems I'm having.

I recorded these by doing "cat /dev/video0 > file".

mysample.mpg
Notice at the beginning and end of the sample when the guys arms are 
flailing against the snow.  Notice the horizontal lines/blocks that are 
showing up.

mysample-2.mpg
When the guy is shaking the girl, notice how pixelated his jacket is.  
This sample really highlights the poor quality/grainiess.

Any ideas oh now to improve it?

Also - when I run "mplayer /dev/video0" it dumps out some useful stuff:

:mplayer /dev/video0
MPlayer 1.0rc2-4.1.2 (C) 2000-2007 MPlayer Team
CPU: Intel(R) Core(TM)2 Quad CPU           @ 2.40GHz (Family: 6, Model: 
15, Stepping: 7)
CPUflags:  MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled with runtime CPU detection.

Playing /dev/video0.
MPEG-PS file format detected.
VIDEO:  MPEG2  720x480  (aspect 2)  29.970 fps  9800.0 kbps (1225.0 kbyte/s)
==========================================================================
Opening video decoder: [mpegpes] MPEG 1/2 Video passthrough
VDec: vo config request - 720 x 480 (preferred colorspace: Mpeg PES)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
The selected video_out device is incompatible with this codec.
Try appending the scale filter to your filter list,
e.g. -vf spp,scale instead of -vf spp.
VDecoder init failed :(
Opening video decoder: [libmpeg2] MPEG 1/2 Video decoder libmpeg2-v0.4.0b
Selected video codec: [mpeg12] vfm: libmpeg2 (MPEG-1 or 2 (libmpeg2))
==========================================================================
==========================================================================
Opening audio decoder: [mp3lib] MPEG layer-2, layer-3
AUDIO: 48000 Hz, 2 ch, s16le, 256.0 kbit/16.67% (ratio: 32000->192000)
Selected audio codec: [mp3] afm: mp3lib (mp3lib MPEG layer-2, layer-3)
==========================================================================
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
Starting playback...
VDec: vo config request - 720 x 480 (preferred colorspace: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.33:1 - prescaling to correct movie aspect.
VO: [x11] 720x480 => 720x540 Planar YV12
[swscaler @ 0x87aaa70]SwScaler: using unscaled yuv420p -> bgr565 special 
converter
A:   5.7 V:   6.3 A-V: -0.679 ct: -0.454 137/137  3%  5%  1.1% 0 0
Exiting... (Quit)



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