libv4l problem decoding frames from pac7302

libv4l problem decoding frames from pac7302

[Németh Márton]

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Hi,

I have some problem that libv4l cannot decode all image coming from the
Labtec Webcam 2200. There are some cases when no image at all can be decoded.
This case can be reproduced always for example by setting the camera to test
mode to produce a color test bar. The raw data arrives from the driver (41472
bytes, see attached) and v4lconvert_convert() returns -1 and the errno is set
to EAGAIN. In this case the v4lconvert_get_error_message() reports the
following error message:

v4l-convert: error decompressing JPEG: Pixart JPEG error: invalid MCU marker: 0xff

Steps to reproduce:
1. get 13327:19c0469c02c3 from http://linuxtv.org/hg/v4l-dvb/
2. apply the patch http://www.spinics.net/lists/linux-media/msg11841.html
3. apply the patch http://www.spinics.net/lists/linux-media/msg11842.html
4. compile and install the new driver
5. plug Labtec Webcam 2200
6. start capturing
7. execute "v4l2-dbg --set-register=0x72 9", this will switch on the color
   test card of the webcam.

Current result: v4lconvert_convert() always return -1 and errno is EAGAIN until
the olor test card is not switched off with "v4l2-dbg --set-register=0x72 0".

How would you start to fix this?

Regards,

	Márton Németh


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Re: libv4l problem decoding frames from pac7302

[Hans de Goede]

Hi,

On 11/08/2009 02:29 PM, Németh Márton wrote:
> Hi,
>
> I have some problem that libv4l cannot decode all image coming from the
> Labtec Webcam 2200. There are some cases when no image at all can be decoded.
> This case can be reproduced always for example by setting the camera to test
> mode to produce a color test bar. The raw data arrives from the driver (41472
> bytes, see attached) and v4lconvert_convert() returns -1 and the errno is set
> to EAGAIN. In this case the v4lconvert_get_error_message() reports the
> following error message:
>
> v4l-convert: error decompressing JPEG: Pixart JPEG error: invalid MCU marker: 0xff
>

See:

libv4lconvert/tinyjpeg.c, lines 1611-1620 for some info on the magical byte
pixart puts between Huffman data blocks.

The 0xff value probably is normal for the test mode, so I would start with trying
to change the MCU test to also except 0xff as a valid MCU marker

Regards,

hans


> Steps to reproduce:
> 1. get 13327:19c0469c02c3 from http://linuxtv.org/hg/v4l-dvb/
> 2. apply the patch http://www.spinics.net/lists/linux-media/msg11841.html
> 3. apply the patch http://www.spinics.net/lists/linux-media/msg11842.html
> 4. compile and install the new driver
> 5. plug Labtec Webcam 2200
> 6. start capturing
> 7. execute "v4l2-dbg --set-register=0x72 9", this will switch on the color
>     test card of the webcam.
>
> Current result: v4lconvert_convert() always return -1 and errno is EAGAIN until
> the olor test card is not switched off with "v4l2-dbg --set-register=0x72 0".
>
> How would you start to fix this?
>
> Regards,
>
> 	Márton Németh
>