[pvrusb2] Fuzzy Video using Hauppauge WinTV PVR USB2

[Mike Isely]

On Mon, 12 Dec 2005, cardboil wrote:

> I am using the Hauppauge WinTV PVR USB2 card and Mike's pvrusb2 driver, with
> MythTV.  When I watch live TV, the picture is a little fuzzy, i.e., when
> there is any motion in the video, it starts to look blurred.  Video that
> doesn't contain a lot of movement looks OK.
>
> Has anyone else encountered this?  Is this an issue with the fact that the
> stream is coming over USB or does it have something to do with my settings
> in Myth?  Is there a way to tell Myth to use the card's hardware
> encoder/decoder or does that happen by default?
>
> Thanks in advance for any guidance.

I'd appreciate hearing if anyone else has seen this effect.  I haven't.

Hmm, have you tried playing with the deinterlace settings in MythTV?

The fact that the stream is coming over USB should not affect anything. 
The "bits" are going to be the same regardless of the transport over which 
they arrive.  MythTV should already be using the card's hardware encoder - 
there's no way to do it any other way right now since the pvrusb2 driver 
is only capable of emitting just the mpeg2 video stream.

USB can in theory add more latency to the video stream, but that will not 
affect its quality.  Since this is mpeg2 compressed video coming over the 
wire, the timing information of the frames is embedded in the stream data 
and therefore does not rely on the timing of the arrival of the data.  So 
long as the stream data arrives quickly enough to not stall anything then 
it should be perfect.

One thing I have found is that if you are receiving a weak signal, then 
the mpeg2 compression in the hardware can make the picture even worse. 
This is because the noise component of the weak signal isn't going to 
compress very well and thus the mpeg2 compression algorithm in the capture 
hardware is probably wasting bandwidth trying to preserve the noise. 
I've seen this effect on weak stations both with my PVR USB2 device and 
through a PVR-250.  The way to mitigate that is to try to digitally filter 
the noise out before the video frames are compressed into mpeg2.  For a 
PVR-250, there are ivtv ioctl() controls you can issue to control such 
filtering.  For the pvrusb2 driver right now that ability does not exist, 
but I know how to do this (it's just some additional control input to the 
encoder chip in the device) and it's on my to-do list.  However from your 
description it sounds like that is not what you are seeing.

MythTV can do various post-processing of a video signal.  For example, it 
can transcode the video down to mpeg4.  This will lower the overall video 
quality (ESPECIALLY it was poor to begin with due to a weak signal as I 
just described).  But you said you saw this during live TV so there 
probably isn't any transcoding going on.

   -Mike

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