Document ffmpeg module

src/ffmpeg.c

@@ -1,5 +1,6 @@
 /** @file ffmpeg.c
- *
+ * Module interfacing with ffmpeg and v4l2. Cointains mainly boilerplate and
+ * tool functions to abstract things a bit
  */
 
 //--includes--------------------------------------------------------------------
@@ -23,10 +24,16 @@ const AVDeviceInfo* find_h264_device(const AVDeviceInfoList* device_list);
 
 //--public functions------------------------------------------------------------
 
+/**
+ * Initialises the ffmpeg module, scanning through the available devices to find
+ * a v4l2 USB device that uses H264 since that would correspond to our webcam
+ */
 int ffmpeg_init(void)
 {
+	//initialises avdevice module
 	avdevice_register_all();
 
+	//list all input devices using v4l2
 	const AVInputFormat* v4l2_format = av_find_input_format("v4l2");
 	AVDeviceInfoList* device_info_list;
 	int device_nb = avdevice_list_input_sources(v4l2_format, nullptr, nullptr,
@@ -41,6 +48,7 @@ int ffmpeg_init(void)
 		return -1;
 	}
 
+	//find a v4l2 device that uses H264
 	const AVDeviceInfo* device = find_h264_device(device_info_list);
 	if (device == nullptr) {
 		fprintf(stderr, "No H264 device found\n");
@@ -62,11 +70,19 @@ void ffmpeg_deinit()
 
 //--local functions-------------------------------------------------------------
 
+/**
+ * Goes through the provided list of input devices and finds the first one to
+ * use H264 encoding and returns it. If no device is found, return a nullptr.
+ *
+ * This function uses v4l2 directly since ffmpeg's interface seems bugged and I
+ * couldn't for the life of me get a result out of it
+ */
 const AVDeviceInfo* find_h264_device(const AVDeviceInfoList* device_list)
 {
 	for (int i=0; i<device_list->nb_devices; ++i) {
 		const AVDeviceInfo* device = device_list->devices[i];
 
+		//opens the descriptor using the v4l2 driver
 		int fd;
 		if ((fd = v4l2_open(device->device_name, O_RDWR)) < 0) {
 			fprintf(stderr, "Failed to open: %s, ignoring...\n",
@@ -74,6 +90,8 @@ const AVDeviceInfo* find_h264_device(const AVDeviceInfoList* device_list)
 			continue;
 		}
 
+		//reads the device formats until H264 is found or there are no more
+		//formats to read
 		bool found = false;
 		struct v4l2_fmtdesc fmt;
 		fmt.index = 0;
@@ -87,6 +105,7 @@ const AVDeviceInfo* find_h264_device(const AVDeviceInfoList* device_list)
 			++fmt.index;
 		}
 
+		//cleanup after ourselves
 		v4l2_close(fd);
 		if (found == true) {
 			return device;