[mythtv-users] v4l Framegrabber Video Quality

[James Crow]

James Crow wrote:
> Brian Wood wrote:
>> On Monday 24 August 2009 12:53:23 James Crow wrote:
>>  
>>> Hello all,
>>>
>>> I recently lost my PVR-500 encoder and rather than purchase a new 
>>> analog
>>> recorder I am falling back to the framegrabbers built into my Pinnacle
>>> 800i QAM/ATSC cards.
>>>
>>> With the PVR-500 bitrate cranked up to 6000-9000 the video was as good
>>> as the cable fed directly into the TV. With the mpeg4 settings on 5000
>>> the quality is still well below the PVR recordings.
>>>
>>> I think I have enough CPU for mpeg4 (Athlon 64 x2 3800+ 2.0GHz). I have
>>> searched the archives and played with the Recording Profile options, 
>>> but
>>> am still not able to get decent quality from the framegrabbers. Does
>>> anyone have some pointers or settings I should try to improve the 
>>> quality?
>>>
>>> I am willing to trade increased disk space for better quality
>>> recordings. I do not store any shows on external media and only watch
>>> shows from a Myth FE.
>>>
>>> Any suggestions?
>>>     
>>
>> Just a few questions to think about:
>>
>> Obviously any sort of encoding can't make things better than the 
>> input video. Have you looked at the output of your frame grabber with 
>> xawtv or some such display program? Does that look as good as you 
>> think it should? Do you have sufficient level going into the capure 
>> card?
>>
>> What sort of problems are you seeing on your recordings? Is it macro 
>> blocking or other digital artifacts, or is it random noise or some 
>> other analog type problem? Does it just look "soft", which can be an 
>> indication of too low a bitrate.
>>
>> Have you tried the RTjpeg option to see if it looks better than the 
>> mpeg4? The file sizes will be bigger, but you said you don't care 
>> about that.
>>
>> What's your CPU usage while encoding? If it's very high you may be 
>> dropping frames.
>>   
>
> Encoding, with two of the four high quality options enabled, is about 
> 40% of one core per recording. This machine is used occasionally for 
> web browsing, but mainly it just handles Myth BE duties.
>
> I need to test outside of Myth to see what xawtv looks like. Signal 
> level should be fine. I have my cable split four ways (3 to myth, 1 to 
> second splitter that feeds tvs). I had no signal problems with the 
> PVR-500 and the Pinnacle cards record QAM (I know digital, but they 
> have signal) just fine.
>
> The analog cable feed, split twice, looks great on our TVs. The main 
> one used for live TV is a cheap 42" RCA. The internal 
> scaler/de-interlacer on it is good, but the PVR recordings using VDPAU 
> de-interlace looked just as good.
>
>
> The recordings have a ghost like outline. Some "blocking" is also 
> visible.
>
> I will try playing around with brightness/contrast/etc with xawtv 
> first. Once I know I have a good picture I will start on the recording 
> options in Myth. I also plan to try the settings from Bruce Markey 
> that were pointed out to me.
>
> Thanks,
> James
Just to follow this thread up with how things stand now, I have decent 
mpeg4 SD recordings. I moved the bitrate up to 4500. The quality options 
are 1 and 15 with min space 3 between frames. None of the four high 
quality boxes are checked. The recordings look very bad without a 
deinterlacer. I currently use JYA's repo and the VDPAU deinterlacer. 
Quality is pretty good and almost approaches the cable fed straight into 
the TV. I have not bothered to look at recording file size because I 
have plenty of storage space.

I can live with this for now. Once .22 is out I may get a HD-PVR and 
record everything in HD. :)

Thanks,
James