Ken,
I had similar problems (on RH7.1 Linux). I found that
VIDIOCSCHAN and VIDIOCGCHAN where a bit tempremental,
and needed to be called at the right time. It failed
when I did a VIDIOCGCHAN first (is this a bug?), and
it needed to have valid values to do a VIDIOCSCHAN.
As I program in C++ (with objects) using other peoples
C code is no good, and I had to find out what was going
wrong, not just copy a working version (useful as they
are)
Jack
----- Original Message -----
From: Ken Hirsch <khirsch11414@xxxxxxxxx>
To: video4linux-list@xxxxxxxxxx
Sent: Tue, 10 Jul 2001 17:56:19 +0100 (GMT+01:00)
Subject: Simple capture (Newbie Question)
> Hello
>
> I am probably repeating a question that has been asked a 1000 times but
> here it goes. I just want to capture an image from my Booktree device
> (WinTV card) and manipulate the stream in memory. I don't care about
> printing it out to screen. I am certainly a newbie programmer and reading
> over the api on the V4L just doesn't sink in enough.
>
> I've been using the code from below (vgrabber.c by Phil Blundell) however
> evrytime I get to the read function the program hangs. I read on the API
> page that not all devices can be read from so I might have to use the mmap
> funtion. However I have not found an example of this that is easy to
> follow for a newbie and was wondering if there was any available.
>
> Also I am having troubles switching tuners (I am trying to go to Composite
> 1 in) can anyone see why this code is failing?
> struct video_channel chan;
> chan.channel=1;
> if (ioctl(fd, VIDIOCGCHAN, &chan) < 0) { perror("VIDIOCGCHAN"); fprintf(stderr, "(" FILE " Didn't Work"); close(fd); exit(1);
> chan.channel=1; chan.type=VIDEO_TYPE_CAMERA;
> if (ioctl(fd, VIDIOCSCHAN, &chan) < 0) { perror("VIDIOGSCHAN"); fprintf(stderr, "(" FILE " Didn't work"); close(fd); exit(1);
>
>
> This code fails at the ioctl VIDIOCSCHAN call.
>
> Thanks for any help you might be able to offer.
>
>
> int main(void)
> { int fd = open(FILE, O_RDONLY), f; struct video_capability cap; struct video_window win; struct video_picture vpic;
> unsigned char *buffer, *src; int bpp = 24, r, g, b; unsigned int i, src_depth;
> if (fd < 0) { perror(FILE); exit(1); }
> if (ioctl(fd, VIDIOCGCAP, &cap) < 0) { perror("VIDIOGCAP"); fprintf(stderr, "(" FILE " not a video4linux device?)\n"); close(fd); exit(1); }
> if (ioctl(fd, VIDIOCGWIN, &win) < 0) { perror("VIDIOCGWIN"); close(fd); exit(1); }
> if (ioctl(fd, VIDIOCGPICT, &vpic) < 0) { perror("VIDIOCGPICT"); close(fd); exit(1); }
> if (cap.type & VID_TYPE_MONOCHROME) { vpic.depth=8; vpic.palette=VIDEO_PALETTE_GREY; /* 8bit grey */ if(ioctl(fd, VIDIOCSPICT, &vpic) < 0) { vpic.depth=6; if(ioctl(fd, VIDIOCSPICT, &vpic) < 0) { vpic.depth=4; if(ioctl(fd, VIDIOCSPICT, &vpic) < 0) { fprintf(stderr, "Unable to find a supported capture format.\n"); close(fd); exit(1); } } } } else { vpic.depth=24; vpic.palette=VIDEO_PALETTE_RGB24;
> if(ioctl(fd, VIDIOCSPICT, &vpic) < 0) { vpic.palette=VIDEO_PALETTE_RGB565; vpic.depth=16;
> if(ioctl(fd, VIDIOCSPICT, &vpic)==-1) { vpic.palette=VIDEO_PALETTE_RGB555; vpic.depth=15;
> if(ioctl(fd, VIDIOCSPICT, &vpic)==-1) { fprintf(stderr, "Unable to find a supported capture format.\n"); return -1; } } } }
> buffer = malloc(win.width * win.height * bpp); if (!buffer) { fprintf(stderr, "Out of memory.\n"); exit(1); }
> do { int newbright; read(fd, buffer, win.width * win.height * bpp); f = get_brightness_adj(buffer, win.width * win.height, &newbright); if (f) { vpic.brightness += (newbright << 8); if(ioctl(fd, VIDIOCSPICT, &vpic)==-1) { perror("VIDIOSPICT"); break; } } } while (f);
> fprintf(stdout, "P6\n%d %d 255\n", win.width, win.height);
> src = buffer;
> for (i = 0; i < win.width * win.height; i++) { READ_VIDEO_PIXEL(src, vpic.palette, src_depth, r, g, b); fputc(r>>8, stdout); fputc(g>>8, stdout); fputc(b>>8, stdout); }
> close(fd);
> }
>
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