Re: go7007 development

[Dean Anderson <dean@sensoray.com>]

Hans Verkuil wrote:
> Hi Pete,
>
> On Friday 17 October 2008 17:21:51 Pete wrote:
>   
>> Hello,
>>
>> I am working on adding the Sensoray 2250 to the go7007 staging tree,
>> starting from GregKH's staging patch here:
>> http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/
>> gregkh-05-staging-2.6.27.patch
>>
>> In particular, we are stuck how to change the MPEG format with
>> standard IOCTL calls.  In particular, this comment in the driver
>> go7007.h below needs explanation:
>>
>> /* DEPRECATED -- use V4L2_PIX_FMT_MPEG and then call
>> GO7007IOC_S_MPEG_PARAMS * to select between MPEG1, MPEG2, and MPEG4
>> */
>> #define V4L2_PIX_FMT_MPEG4     v4l2_fourcc('M','P','G','4') /* MPEG4 
>>        */
>>
>> The existing driver, for backward-compatibility , allowed
>> V4L2_PIX_FMT_MPEG4 to be used for v4l2_format.pixelformat with
>> VIDIOC_S_FMT.
>>
>> GO7007IOC_S_MPEG_PARAMS is a custom ioctl call and we would rather
>> have this done through v4l2 calls. We also can't seem to find where
>> MPEG1, MPEG2, and MPEG4 elementary streams are defined in the V4L2
>> API.  We checked other drivers, but could not find anything.  The
>> closest thing we found was the V4L2_CID_MPEG_STREAM_TYPE control, but
>> the enums do not define elementary streams nor MPEG4.
>>
>> Your advice is appreciated.
>>
>> Thanks.
>>     
>
> It would be really nice to have this driver in the kernel.
>
> All MPEG streams use V4L2_PIX_FMT_MPEG and set the exact stream type 
> through V4L2_CID_MPEG_STREAM_TYPE. You probably need to add a few new 
> stream types to this control for the elementary streams. I think 
> something like TYPE_MPEG_ELEM might do the trick, and then you can use 
> the audio and video encoding controls to select the precise audio/video 
> encoding.
>
> I don't know enough about the capabilities, so perhaps 
> TYPE_MPEG1/2/4_ELEM is required instead of a more generic 
> TYPE_MPEG_ELEM.
>
>   
The generic approach seems better.  There will be boards with H264 
encapsulated in MPEG2 transport stream.  I'd recommend keeping the 
encapsulation/mux format in V4L2_CID_MPEG_STREAM_TYPE, but not 
necessarily the encoding. 

Otherwise you'll have V4L2_MPEG_STREAM_TYPE_MPEG2_TS_MPEG4_ENCODING, 
etc..  Maybe V4L2_CID_MPEG_STREAM_TYPE needs a comment that it is the 
encapsulation(or mux format), and the encoding should be defined in 
V4L2_CID_MPEG_VIDEO_ENCODING?

So for this Go7007, we suggest adding V4L2_MPEG_STREAM_TYPE_ELEM to 
V4L2_CID_MPEG_STREAM_TYPE.
We also suggest adding V4L2_MPEG_VIDEO_ENCODING_MPEG_4 to 
V4L2_CID_MPEG_VIDEO_ENCODING.  Of course, there is the question of what 
version of MPEG4, but we'll leave that for another day.

What do you think?

> Since I designed the MPEG API for V4L2 I guess I'm the right person to 
> help you. I also have a Plextor TV402U since I always wanted to get the 
> go7007 driver into the kernel, but I never had the time so I'm glad 
> you've picked it up.
>
> Regards,
>
> 	Hans
>
>   
Good to hear, and thanks for the quick response.

Dean

-- 
Dean Anderson
Sensoray Co., Inc.
Email: dean@sensoray.com
http://www.sensoray.com



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