On Mon, 22 Jun 2009, Andy Walls wrote:
On Sun, 2009-06-21 at 22:39 -0500, Theodore Kilgore wrote:
Andy,
You are right. Your camera is emitting JPEG while streaming. I just
succeeded in creating an image which resembles your test picture by
extracting the frame data for one frame, tacking on a header, and running
hex2bin on the combined file. I did not get the thing quite right, because
your header is from your JPEG photo (640x480) and your stream is probably
320x240. But I got something out which is obviously recognizable.
Excellent. Going from "It may never work" to "something recognizable"
in one weekend is good progress.
Well, sometimes the easy and obvious just works, and one is lucky. If only
they were all that easy. Besides, as we well know, this list is a place
where geniuses hang out. So perhaps some of the pixie dust has rubbed off
on us.
Therefore with a little bit of further tweaking it will presumably come
out exactly so. Namely, I have to remember where to stick the two
dimensions into the header.
Yes, as far as I'm concerned the problem is solved. The details are
left as an exercise for the reader. ;)
I will try to get on it. There is nothing left but details, but there are
lots of those. The first one is to get the header exactly right. Then
there is the question, what is _my_ camera doing? I did not check that
yet. And so on. So it is an algorithm now, but many steps remain to be
completed.
I'm not up to speed on Linux webcam kernel to userspace API details.
However, might I suggest going forward for testing at least, that when
one starts the webcam streaming, the driver emit the stream in the form
of an AVI. You'd need an AVI header declaring only an MJPEG 'vids'
stream - no 'auds' nor 'idx' - and a 'movi' section with RIFF/AVI chunks
that have MJPEG headers and the webcam payload.
For all I know, it might be just a matter of following down a standard
path. Perhaps this is all handled already in libv4lconvert, and it is
merely a matter of plugging into that. I haven't checked yet, but that is
more or less what I expect right now.
I haven't seen evidence that audio comes from the webcam when it is
streaming, but I haven't looked very much either.
Same. Actually, my impression is that these cameras can not walk and chew
gum at the same time. I would suspect that the audio is an either/or kind
of thing. Either on, and it can record audio but not stream it, or off. I
would be very surprised if an el cheapo like the one I have could do more.
I could be wrong, of course. Perhaps both of us ought to check closely.
As my students in courses like calculus say,
"Sir, it has been a long time since I studied that." Whereupon I reply,
"With my white hair, I wonder how far I could get with that excuse?"
:)
I will send you a copy of the results for your amusement. It is obviously
the first attempt, so do not laugh at the fact that you get two copies of
3
x6
--
side by side, please.
In retrospect, I should have used the 6x7 (or 6x9) flash card, so the
answer would have been 42. :)
Well, then there would be no mysteries left, would there? We couldn't have
that.
This is Monday, and I have to go off to the salt mine. I may be able to
get back to this after coming home from the class.
Theodore Kilgore
--
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
