[pvrusb2] Some MPEG-controls questions

[Hans Verkuil]

On Thursday 26 February 2009 10:51:24 Carsten Meier wrote:
> Hi again,
>
> now I'm allowing users to change all controls on a channel-switch,
> including MPEG ones. (To make the filter-controls accessible) Is it save
> to change e.g. V4L2_CID_MPEG_VIDEO_BITRATE_PEAK during streaming? If I
> change it during streaming video to vlc through the sysfs-interface,
> vlc crashes. But I don't know if this is due to a corrupted stream or
> just a bug in vlc. Is it save to change even the stream type? Or should
> I better stop and restart streaming on a channel-switch due to possible
> stream-parameter changes?

Looking at the code pvrusb2 is supposed to remember the change but only 
apply it the next time a capture is started. A lot of these properties 
cannot be modified on the fly. I'm not entirely sure whether pvrusb2 takes 
the correct approach by remembering the change for the next time. ivtv for 
example just returns -EBUSY.

How pvrusb2 handles these requests when they come from the sysfs interface, 
that's something Mike can answer.

> Another less important question: What is meant by "audio emphasis"?

audio emphasis: Filtering applied to an audio signal before storage or 
transmission to improve the signal-to-noise ratio at high frequencies.

It's part of the MPEG specification, but normally this is always set to 
None.

I've tried to find out when the other emphasis options might be used, but it 
is hard to get decent information on that. I know I read something about 
this in the past, but I can't remember where. It would actually be useful 
if someone knows more about this so that I can improve the v4l2 
specification.

Regards,

	Hans

-- 
Hans Verkuil - video4linux developer - sponsored by TANDBERG