Hi all
Let me try to further elaborate on this topic. So far, I think, the
following provides the cleanest solution to our quick format-switching /
multiple video-queue problem:
On Wed, 16 Feb 2011, Guennadi Liakhovetski wrote:
> (2) cleanly separate setting video data format (S_FMT) from specifying the
> allocated buffer size.
The control flow then would look like:
struct v4l2_requestbuffers req;
fd = open();
/* initialise and configure the first "still-shot" buffer-queue */
bufq.id = -EINVAL;
ret = ioctl(fd, VIDIOC_BUFQ_SELECT, &bufq);
/*
* bufq.id now contains a handle to a newly allocated videobuf
* queue, it also becomes the current queue.
*/
still_qid = buf.id;
/*
* specify explicitly required buffer size - use one of reserved
* fields
*/
req.size = still_x * still_y * bpp;
ret = ioctl(fd, VIDIOC_REQBUFS, &req);
for (i = 0; i < req.count; i++) {
buf.index = i;
ret = ioctl(fd, VIDIOC_QUERYBUF, &buf);
start = mmap();
ret = ioctl(fd, VIDIOC_QBUF, &buf);
}
/* Allocate a second "preview" queue */
bufq.id = -EINVAL;
ret = ioctl(fd, VIDIOC_BUFQ_SELECT, &bufq);
preview_qid = bufq.id;
req.size = preview_x * preview_y * bpp;
ret = ioctl(fd, VIDIOC_REQBUFS, &req);
for (i = 0; i < req.count; i++) {
buf.index = i;
ret = ioctl(fd, VIDIOC_QUERYBUF, &buf);
start = mmap();
ret = ioctl(fd, VIDIOC_QBUF, &buf);
}
/* Stay on the preview queue */
ret = ioctl(fd, VIDIOC_STREAMON, &type);
for (i = 0; i < n; i++) {
ret = ioctl(fd, VIDIOC_DQBUF, &buf);
ret = ioctl(fd, VIDIOC_QBUF, &buf);
}
ret = ioctl(fd, VIDIOC_STREAMOFF, &type);
/* Switch to the still-shot queue */
bufq.id = still_qid;
ret = ioctl(fd, VIDIOC_BUFQ_SELECT, &bufq);
ret = ioctl(fd, VIDIOC_STREAMON, &type);
for (i = 0; i < n; i++) {
ret = ioctl(fd, VIDIOC_DQBUF, &buf);
ret = ioctl(fd, VIDIOC_QBUF, &buf);
}
ret = ioctl(fd, VIDIOC_STREAMOFF, &type);
And so on. If the above is _conceptually_ acceptable, we need 1 to 2 new
ioctl()s and an extension to the VIDIOC_REQBUFS ioctl() to specify the
buffer size. I wrote "1 or 2 new ioctl()s," because above the new
VIDIOC_BUFQ_SELECT ioctl() performs two functions: if the handle is
negative, it allocates a new queue, if it containes a valid (per-device or
per file-handle?) queue ID, it switches to it. We might also decide to use
two ioctl()s for these two functions.
Comments?
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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