Add details about USB cameras

source/_components/ffmpeg.markdown

@@ -25,7 +25,7 @@ ffmpeg:
 
 Configuration variables:
 
-- **ffmpeg_bin** (*Optional*): Default 'ffmpeg'. The name or path to the `ffmpeg` binary.
+- **ffmpeg_bin** (*Optional*): Default `ffmpeg`. The name or path to the `ffmpeg` binary.
 - **run_test** (*Optional*): Default True. Check if `input` is usable by ffmpeg.
 
 ### {% linkable_title Raspbian Debian Jessie Lite Installations %}
@@ -36,7 +36,9 @@ $ sudo echo "deb http://ftp.debian.org/debian jessie-backports main" >> /etc/apt
 $ sudo apt-get update
 $ sudo apt-get -t jessie-backports install ffmpeg
 ```
+
 We can use now following in the configuration:
+
 ```
 ffmpeg:
   ffmpeg_bin: /usr/bin/ffmpeg
@@ -52,7 +54,44 @@ First check that your stream is playable by `ffmpeg` outside of Home Assistant w
 $ ffmpeg -i INPUT -an -f null -
 ```
 
-Now you should be able to see what is going wrong.  The following list contains some common problems and solutions:
+Now you should be able to see what is going wrong. The following list contains some common problems and solutions:
 
 - `[rtsp @ ...] UDP timeout, retrying with TCP`: You need to set an RTSP transport in the configuration with: `input: -rtsp_transport tcp -i INPUT`
 - `[rtsp @ ...] Could not find codec parameters for stream 0 (Video: ..., none): unspecified size`: FFmpeg needs more data or time for autodetection (the default is 5 seconds). You can set the `analyzeduration` and/or `probesize` options to experiment with giving FFmpeg more leeway. If you find the needed value, you can set it  with: `input: -analyzeduration xy -probesize xy -i INPUT`. More information about this can be found [here](https://www.ffmpeg.org/ffmpeg-formats.html#Description).
+
+#### {% linkable_title USB cameras %}
+
+For `INPUT` a valid source is needed. USB camera are an easy way to test your video setup. To get all available USB cameras connected to the system, eg. use the v4l2 tools on a Linux machine.
+
+```bash
+$ v4l2-ctl --list-devices
+UVC Camera (046d:0825) (usb-0000:00:14.0-1):
+	/dev/video1
+
+Integrated Camera (usb-0000:00:14.0-10):
+	/dev/video0
+```
+
+Record a test video with your USB device `/dev/video1`:
+
+```bash
+$ ffmpeg -i /dev/video1 -codec:v libx264 -qp 0 lossless.mp4
+[...]
+Input #0, video4linux2,v4l2, from '/dev/video1':
+  Duration: N/A, start: 43556.376974, bitrate: 147456 kb/s
+    Stream #0:0: Video: rawvideo (YUY2 / 0x32595559), yuyv422, 640x480, 147456 kb/s, 30 fps, 30 tbr, 1000k tbn, 1000k tbc
+[...]
+Output #0, mp4, to 'lossless.mp4':
+  Metadata:
+    encoder         : Lavf57.41.100
+    Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv422p, 640x480, q=-1--1, 30 fps, 15360 tbn, 30 tbc
+    Metadata:
+      encoder         : Lavc57.48.101 libx264
+    Side data:
+      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
+Stream mapping:
+  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
+Press [q] to stop, [?] for help
+frame=  223 fps= 40 q=-1.0 Lsize=   16709kB time=00:00:07.40 bitrate=18497.5kbits/s dup=58 drop=0 speed=1.32x
+```
+