capture_open(...) 打开设备
void *capture_open (const char *dev_name, int t_width, int t_height)
{
int id = open(dev_name, O_RDWR);
if (id < 0) return 0;
Ctx *ctx = new Ctx;
ctx->vid = id;
// to query caps
v4l2_capability caps;
ioctl(id, VIDIOC_QUERYCAP, &caps);
if (caps.capabilities & V4L2_CAP_VIDEO_CAPTURE) {
if (caps.capabilities & V4L2_CAP_READWRITE) {
// TODO: ...
}
if (caps.capabilities & V4L2_CAP_STREAMING) {
// 检查是否支持 MMAP, 还是 USERPTR
v4l2_requestbuffers bufs;
memset(&bufs, 0, sizeof(bufs));
bufs.count = 2;
bufs.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
bufs.memory = V4L2_MEMORY_MMAP;
if (ioctl(id, VIDIOC_REQBUFS, &bufs) < 0) {
fprintf(stderr, "%s: don't support MEMORY_MMAP mode!/n", __func__);
close(id);
delete ctx;
return 0;
}
fprintf(stderr, "%s: using MEMORY_MMAP mode, buf cnt=%d/n", __func__, bufs.count);
// mmap
for (int i = 0; i < 2; i++) {
v4l2_buffer buf;
memset(&buf, 0, sizeof(buf));
buf.type = bufs.type;
buf.memory = bufs.memory;
if (ioctl(id, VIDIOC_QUERYBUF, &buf) < 0) {
fprintf(stderr, "%s: VIDIOC_QUERYBUF ERR/n", __func__);
close(id);
delete ctx;
return 0;
}
ctx->bufs[i].length = buf.length;
ctx->bufs[i].start = mmap(0, buf.length, PROT_READ|PROT_WRITE,
MAP_SHARED, id, buf.m.offset);
}
}
else {
fprintf(stderr, "%s: can't support read()/write() mode and streaming mode/n", __func__);
close(id);
delete ctx;
return 0;
}
}
else {
fprintf(stderr, "%s: can't support video capture!/n", __func__);
close(id);
delete ctx;
return 0;
}
int rc;
// enum all support image fmt
v4l2_fmtdesc fmt_desc;
uint32_t index = 0;
// 看起来, 不支持 plane fmt, 直接使用 yuyv 吧, 然后使用 libswscale 转换
#if 0
do {
fmt_desc.index = index;
fmt_desc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
rc = ioctl(id, VIDIOC_ENUM_FMT, &fmt_desc);
if (rc >= 0) {
fprintf(stderr, "/t support %s/n", fmt_desc.description);
}
index++;
} while (rc >= 0);
#endif // 0
v4l2_format fmt;
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
rc = ioctl(id, VIDIOC_G_FMT, &fmt);
if (rc < 0) {
fprintf(stderr, "%s: can't VIDIOC_G_FMT.../n", __func__);
return 0;
}
PixelFormat pixfmt = PIX_FMT_NONE;
switch (fmt.fmt.pix.pixelformat) {
case V4L2_PIX_FMT_YUYV:
pixfmt = PIX_FMT_YUYV422;
break;
}
if (pixfmt == PIX_FMT_NONE) {
fprintf(stderr, "%s: can't support %4s/n", __func__, (char*)&fmt.fmt.pix.pixelformat);
return 0;
}
// 构造转换器
fprintf(stderr, "capture_width=%d, height=%d, stride=%d/n", fmt.fmt.pix.width, fmt.fmt.pix.height,
fmt.fmt.pix.bytesperline);
ctx->width = t_width;
ctx->height = t_height;
ctx->sws = sws_getContext(fmt.fmt.pix.width, fmt.fmt.pix.height, pixfmt,
ctx->width, ctx->height, PIX_FMT_YUV420P, // PIX_FMT_YUV420P 对应 X264_CSP_I420
SWS_FAST_BILINEAR, 0, 0, 0);
ctx->rows = fmt.fmt.pix.height;
ctx->bytesperrow = fmt.fmt.pix.bytesperline;
avpicture_alloc(&ctx->pic_target, PIX_FMT_YUV420P, ctx->width, ctx->height);
// queue buf
for (int i = 0; i < sizeof(ctx->bufs)/sizeof(Buffer); i++) {
v4l2_buffer buf;
memset(&buf, 0, sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (ioctl(id, VIDIOC_QBUF, &buf) < 0) {
fprintf(stderr, "%s: VIDIOC_QBUF err/n", __func__);
exit(-1);
}
}
int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (ioctl(id, VIDIOC_STREAMON, &type) < 0) {
fprintf(stderr, "%s: VIDIOC_STREAMON err/n", __func__);
exit(-1);
}
return ctx;
}
capture_get_pic()
VIDIOC_DQBUF // 出列,
sws_scale // 格式转换/拉伸到 PIX_FMT_YUV420P, 准备方便压缩
VIDIOC_QBUF // 重新入列
