Re: V4L2_PIX_FMT_RAW

[Thomas Kaiser <linux-dvb@kaiser-linux.li>]

H. Willstrand wrote:
> On Wed, Feb 20, 2008 at 10:11 PM, Thomas Kaiser
> <linux-dvb@kaiser-linux.li> wrote:
>> H. Willstrand wrote:
>>  > On Wed, Feb 20, 2008 at 9:42 PM, Thomas Kaiser
>>  > <linux-dvb@kaiser-linux.li> wrote:
>>  >> H. Willstrand wrote:
>>  >>  > On Wed, Feb 20, 2008 at 9:22 PM, Thomas Kaiser
>>  >>  > <linux-dvb@kaiser-linux.li> wrote:
>>  >>  >> H. Willstrand wrote:
>>  >>  >>  > On Wed, Feb 20, 2008 at 8:25 PM, Thomas Kaiser
>>  >>  >>  > <linux-dvb@kaiser-linux.li> wrote:
>>  >>  >>  >> Why is V4L2_PIX_FMT_RAW not included as a pixel format in V4l2?
>>  >>  >>  >>
>>  >>  >>  >>  I would like to just forward the stream from my webcam "as it is" to user space .
>>  >>  >>  >>
>>  >>  >>  >>  V4L2_PIX_FMT_RAW looks as it is the right thing I need.
>>  >>  >>  >>
>>  >>  >>  >
>>  >>  >>  > V4L2 drivers should not perform any video transformations, the driver
>>  >>  >>  > provides user space with hardware supported formats.
>>  >>  >>
>>  >>  >>  Ok, so, I need a entry for Pixart chips.
>>  >>  >>  PAC207: a line based coding algo.
>>  >>  >>  PAC7311: the interpretation of JPEG from Pixart
>>  >>  >>  PAC7302: the _new_  interpretation of JPEG from Pixart
>>  >>  >>
>>  >>  >>  V4L2_PIX_FMT_RAW would make my live easier.
>>  >>  >>
>>  >>  >>  The option to forward the stream "as it is" would be really nice. When the
>>  >>  >>  manufacture of some video streaming devices (like webcams) do their own thing,
>>  >>  >>  you can forward the raw stream and the user application can take care of the
>>  >>  >>  decoding of the stream.
>>  >>  >>
>>  >>  >>  For me it looks not like such a bad idea!!!???
>>  >>  >>
>>  >>  >
>>  >>  > Yes, it might be a good idea to add something like V4L2_PIX_FMT_PAC207, etc.
>>  >>  > This is anyhow the case with the PWC family.
>>  >>
>>  >>  I think the better is to just forward the stream to userspace.
>>  >>  Then we have to make a lib which can be called from all these video application
>>  >>  around to decode the stream.
>>  >>
>>  >>  Somebody talked already about this on the list.
>>  >>
>>  >>  When the cam is able to send a stream in a good known format it is no problem to
>>  >>  handle this with the right V4L2_PIX_FMT_..., but if not, we need a "official"
>>  >>  way to get this "devil" stream to user space!
>>  >>
>>  >
>>  > Well, it can go ugly if one piece of hardware supports several "raw"
>>  > formats, they need to be distinct. And in the end of the day the V4L2
>>  > drivers might consist of several identical "raw" formats which then
>>  > aren't consolidated.
>>  >
>>  > Harri
>>
>>  I don't really understand what you try to say here.
>>  I want to have the stream forwarded "as it is" to user space. Then the v4l2
>>  driver even have not to know what kind of stream this is!
>>  We just forward the stream (again) "as it is" to user space.
>>  Now, the user space application (viewer app, skype or what ever) has to decide
>>  if they can handle the stream.
>>
> Ok, if a driver exposes a RAW format, how can a application know if it
> can handle the format? By looking at the driver name? What if the
> driver have several RAW formats? (they might have)

How does the driver know how to handle the raw stream?

OK, I get USB ID and can guess it should be this format but it is not always 
like this.

Anyway, All information the driver uses to get know the stream can be forwarded 
to user space. We just need the interface for this.
Usually, the SOF gives you the information you need. And this will be included 
when you forward the stream "as it is".

> 
> Next, standardization is a good thing, and hopefully chip set vendors
> tries to keep down the number of formats, so it's a good idea to try
> define distinct V4L2_PIX_FMT for each distinct format.

I don't think that chip set manufacture will look at a "Standard", They just try 
to optimize there chip and lower the cost of manufacturing.

They are not interested in standards. Standards means everybody can copy it!

Thomas

> 
> Cheers,
> Harri
> 
> 
>>  PS: Why do you answer OFF-LIST? I think it is a nice topic to discussed with
>>  everyone on the list.
> I thought I did, sorry for that.
> 
> //Harri


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