This project demonstrates how to get video from webcams using only Linux's native V4L2 (Video For Linux version 2) interface. It includes a basic C library for managing webcams and getting video frames.
First, install SDL2, which the demo depends on (the library itself doesn't need SDL, though, so only do this if you care about the demo program):
sudo apt install libsdl2-dev
Run make, followed by ./sdl_camera /dev/video0. This should print
information about the camera and show a window displaying a video feed from the
camera.
The webcam usage library is contained in webcam_lib.h and webcam_lib.c.
A full set of the intended API is available by reading webcam_lib.h, which
includes comments on how to use all of the functions. To use the library,
simply #include <webcam_lib.h> and ensure that webcam_lib.c (or a compiled
version of it) is provided to the compiler.
#include <stddef.h>
#include <stdio.h>
#incldue <stdlib.h>
#include "webcam_lib.h"
static void ErrorExit(char *message) {
printf("%s\n", message);
exit(1);
}
int main(void) {
WebcamInfo webcam;
WebcamResolution resolution;
void *pixel_data = NULL;
size_t pixel_data_size = 0;
if (!OpenWebcam("/dev/video0", &webcam)) {
ErrorExit("Failed opening webcam");
}
// This takes an array of resolutions, but we only care about getting the
// first one.
if (!GetSupportedResolutions(&webcam, &resolution, 1)) {
ErrorExit("Failed getting resolution");
}
if (!SetResolution(&webcam, resolution.width, resolution.height)) {
ErrorExit("Failed setting resolution");
}
if (!BeginLoadingNextFrame(&webcam)) {
ErrorExit("Failed starting to load a frame");
}
if (!GetFrameBuffer(&webcam, &pixel_data, &pixel_data_size)) {
ErrorExit("Failed getting pixel data");
}
// Now, pixel_data will contain the frame, in the YUYV (aka YUY2) format.
// Either use it as-is, or maybe use ConvertYUYVToRGBA(...) to convert it to
// the RGBA format. pixel_data does *not* need to be unmapped or freed--that
// will be taken care of by CloseWebcam if necessary.
// Finally, close the camera and clean up resources:
CloseWebcam(&webcam);
return 0;
}