Mailing List Archive: ivtv: devel

Re: Quality Issues

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duncan-v4l at linuxowl

Apr 23, 2007, 11:25 AM

Post #1 of 4 (1287 views)
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Re: Quality Issues

Duncan Webb wrote:
> Hi all,
>
> I've been noticing some quality issues with ivtv over the last months or
> so and am wondering if anybody else has the same issues.
>
> I have two types of Hauppauge PVR cards, a 350 and a 500. both running
> ivtv-0.10.1
>
> ivtv0: Encoder revision: 0x02060039
> ivtv0: Decoder revision: 0x02020023
>
> The PVR-350 is very jerky but the picture is quite sharp, at least as
> sharp as the TV.

Thanks to one of the Freevo users who spotted the problem. The
video_aspect and the video_b_frames start at 1 less than with the
drivers before 0.8.0. This means that the video_aspect was being set to
16x9 instead of 4x3 and the b-frames was being set to 3 instead of 2.

However having said the above I don't quite understand why the aspect
being set to 16x9 and the b-frames being set to 3 in a video_gop_size of
12 should make the mpeg stream jerky.

This leads to the question, what does the video_aspect control setting
actually do?

One other observation is that the default Video standard is now
0x0000000f whereas it was 0x000000ff. Will this have an effect on the
quality?

I've not yet had time to see if the default setting make a difference
with the quality of the picture on the PVR-500.

TIA
Duncan

>
> The PVR-500 has a smooth image but the picture is not sharp.
>
> The signal strength is good
>
> PVR-350 # v4l2-ctl -T
> Tuner:
> Capabilities : 62.5 kHz multi-standard stereo lang1 lang2
> Frequency range : 44.0 MHz - 958.0 MHz
> Signal strength : 99%
> Current audio mode : stereo
> Available subchannels: stereo
>
> The PVR-500 has a smooth image but the picture is not sharp.
>
> PVR-500 # v4l2-ctl -T
> Tuner:
> Capabilities : 62.5 kHz multi-standard stereo lang1 lang2
> Frequency range : 44.0 MHz - 958.0 MHz
> Signal strength : 100%
> Current audio mode : lang1
> Available subchannels: stereo
>
> The attached images show, quite clearly with the white jumper the
> difference in image quality.

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duncan-v4l at linuxowl

May 1, 2007, 10:42 PM

Post #2 of 4 (1154 views)
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Re: Quality Issues [In reply to]

> Duncan Webb wrote:
>> Hi all,
>>
>> I've been noticing some quality issues with ivtv over the last months or
>> so and am wondering if anybody else has the same issues.
>
> One other observation is that the default Video standard is now
> 0x0000000f whereas it was 0x000000ff. Will this have an effect on the
> quality?
>
> I've not yet had time to see if the default setting make a difference
> with the quality of the picture on the PVR-500.

Sorry to reply to my own post yet again.

I think that I've found why the picture quality is poorer with the PVR-500.

The temporal_filter is being set to 8.

The question is why, as I've not yet tracked down the reason. It's quite
possible that I've screwed up something in my own code mapping the old
codec information to the v4l2 external controls.

Is it possible that the driver sets the temporal_filter during other
operations, such as set format?

Why is this only being set with the PVR-500 and not with the PVR-350?

Any hints?

TIA
Duncan

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duncan-v4l at linuxowl

May 2, 2007, 10:25 AM

Post #3 of 4 (1147 views)
Permalink

Re: Quality Issues [In reply to]

Duncan Webb wrote:
>> Duncan Webb wrote:
>>> Hi all,
>>>
>>> I've been noticing some quality issues with ivtv over the last months or
>>> so and am wondering if anybody else has the same issues.
>> One other observation is that the default Video standard is now
>> 0x0000000f whereas it was 0x000000ff. Will this have an effect on the
>> quality?
>>
>> I've not yet had time to see if the default setting make a difference
>> with the quality of the picture on the PVR-500.
>
> Sorry to reply to my own post yet again.
>
> I think that I've found why the picture quality is poorer with the PVR-500.
>
> The temporal_filter is being set to 8.
>
> The question is why, as I've not yet tracked down the reason. It's quite
> possible that I've screwed up something in my own code mapping the old
> codec information to the v4l2 external controls.
>
> Is it possible that the driver sets the temporal_filter during other
> operations, such as set format?
>
> Why is this only being set with the PVR-500 and not with the PVR-350?

Well this is pretty obvious why when I determined that it was
VIDIOC_S_FMT call that was changing the temporal_filter.

in driver/ivtv-ioctl.c
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 18)
if (itv->params.width != 720 || itv->params.height !=
(itv->is_50hz ? 576 : 480))
itv->params.video_temporal_filter = 0;
else
itv->params.video_temporal_filter = 8;
#endif

Any reason for the temporal_filter being over written?

Duncan

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bmayland at leoninedev

May 4, 2007, 6:49 AM

Post #4 of 4 (1128 views)
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Re: Quality Issues [In reply to]

Duncan Webb wrote:
> Well this is pretty obvious why when I determined that it was
> VIDIOC_S_FMT call that was changing the temporal_filter.
>
> in driver/ivtv-ioctl.c
> #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 18)
> if (itv->params.width != 720 || itv->params.height !=
> (itv->is_50hz ? 576 : 480))
> itv->params.video_temporal_filter = 0;
> else
> itv->params.video_temporal_filter = 8;
> #endif
>
> Any reason for the temporal_filter being over written?
>
Setting it to 0 when the video frame size wasn't "full resolution"
was added because the temporal filter created some horrible ghosting
artifacts at other resolutions. This was probably back in 2005 when the
default was 8.

Now the default is 0 iirc, so maybe this code should be modified
accordingly?

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