Re: My Microdia (SN9C201) webcam doesn't work properly in Linux anymore

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 03/05/2012 01:03 PM, Jean-Francois Moine wrote:
> On Mon, 05 Mar 2012 09:33:18 +0100
> Hans de Goede<hdegoede@redhat.com>  wrote:
>
>> I guess that motion is using the JPG compressed frames rather then
>> the i420 like special format these cameras also support, and it looks
>> like we don't reserve enoug space to buffer these frames. To fix this
>> we need to enlarge the size we reserve per frame in the sn9c20x driver,
>> edit sn9c20x.c and search for vga_mode, in that table you will
>> find a factor "4 / 8" (its in there 3 times), change all 3 occurences
>> to "5 / 8" and try again, then "6 / 8", etc.
>>
>> Normally I would be suspicious about SOF / EOF detection when we
>> need such a factor, but the timestamps in your log exactly match 30
>> fps, so that seems to be fine. And in my experience with the USB bandwidth
>> stuff the sn9c20x does seem to compress less then other JPG cams, so
>> it makes sense that it needs bigger buffers to store the frames too.
>
> Hi Hans,
>
> The JPEG compression quality of the sn9c20x is 95%. That's why the
> frames are so big. Then, if the quality is not settable, I wonder why
> to use the JPEG format.

I think the quality is settable, and we are just not setting it to a very
useful value. I'm afraid I don't have time to work on this atm, but if you
are willing to take a shot at this, then I can test (I've such a camera).

I'll send you a private mail with info on how to set the compression
ratio.

> BTW, I wonder also about the SN9C20X_I420: this format asks for a
> buffer greater than the native image.

Yes, but then the data is ready to use, since most apps actuall want i420,
where as raw bayer needs a lot of CPU intensive processing before we get
useful data out of it.

Regards,

Hans