Daniel, Many thanks for your mail. Please excuse the naivety of my questions - I'm a h/w guy and a nube to the s/w world. > -----Original Message----- > From: Daniel Glöckner [mailto:daniel-gl@xxxxxxx] > Sent: 09 November 2010 09:10 > To: Michael PARKER > Cc: linux-media@xxxxxxxxxxxxxxx > Subject: Re: Format of /dev/video0 data for HVR-4000 frame grabber > > On Tue, Nov 09, 2010 at 09:43:29AM +0100, Michael PARKER wrote: > > I'm attempting to capture a single frame from the /dev/video0 output of > > my HVR-4000 card's analogue tuner as a JPEG. > > > > Whilst several resources exist for capturing the output of a card with > > h/w MPEG compression, I'm unable to determine the format of the > > /dev/video0 data for a frame grabber such as the HVR-4000. > > According to the sourcecode the cx88 chip can do 8 bit grayscale, > 15/16/24/32 bit RGB/BGR, and two variants of 4:2:2 YCbCr. Do you know which of these is the default format or how to determine the format I'm seeing coming out of /dev/video0? Do you have a suggestion for how data captured from /dev/video0 can be converted into a recognisable image format (JPEG, GIF, PNG etc.)? I'm keen, if possible, to grab the single frame image using just command line tools and without recourse to ioctls, compiled code etc. > > Can anyone suggest a means by which I can capture a single frame from a > > frame grabber card? Can I just use "dd if=/dev/video0 of=image.jpg bs=64K" > > or similar or do I have to access the card via the V4L2 drivers? > > Yes, dd should work but you need to use a blocksize that can hold a > complete frame and count=1 if you want a single frame. JPEG, as > mentioned above, is not possible with this board. Presumably blocksize is just x * y * depth? Do you happen to know the default x/y for the cx88 output? I assume that x/y can be set via ioctls but, as stated earlier, I'm keen to avoid writing/compiling code if I can. Do I need to make any allowance for any form of header within the blocksize? Also, how do I synchronise dd to the beginning of a new frame (and thus avoid capturing sections of two frames)? Thanks again, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
