BIG docs refactoring

internal/exec/README.md

@@ -1,3 +1,39 @@
+# Exec
+
+Exec source can run any external application and expect data from it. Two transports are supported - **pipe** ([`new in v1.5.0`](https://github.com/AlexxIT/go2rtc/releases/tag/v1.5.0)) and **RTSP**.
+
+If you want to use **RTSP** transport, the command must contain the `{output}` argument in any place. On launch, it will be replaced by the local address of the RTSP server.
+
+**pipe** reads data from app stdout in different formats: **MJPEG**, **H.264/H.265 bitstream**, **MPEG-TS**. Also pipe can write data to app stdin in two formats: **PCMA** and **PCM/48000**.
+
+The source can be used with:
+
+- [FFmpeg](https://ffmpeg.org/) - go2rtc ffmpeg source just a shortcut to exec source
+- [FFplay](https://ffmpeg.org/ffplay.html) - play audio on your server
+- [GStreamer](https://gstreamer.freedesktop.org/)
+- [Raspberry Pi Cameras](https://www.raspberrypi.com/documentation/computers/camera_software.html)
+- any of your own software
+
+## Configuration
+
+Pipe commands support parameters (format: `exec:{command}#{param1}#{param2}`):
+
+- `killsignal` - signal which will be sent to stop the process (numeric form)
+- `killtimeout` - time in seconds for forced termination with sigkill
+- `backchannel` - enable backchannel for two-way audio
+- `starttimeout` - time in seconds for waiting first byte from RTSP
+
+```yaml
+streams:
+  stream: exec:ffmpeg -re -i /media/BigBuckBunny.mp4 -c copy -rtsp_transport tcp -f rtsp {output}
+  picam_h264: exec:libcamera-vid -t 0 --inline -o -
+  picam_mjpeg: exec:libcamera-vid -t 0 --codec mjpeg -o -
+  pi5cam_h264: exec:libcamera-vid -t 0 --libav-format h264 -o -
+  canon: exec:gphoto2 --capture-movie --stdout#killsignal=2#killtimeout=5
+  play_pcma: exec:ffplay -fflags nobuffer -f alaw -ar 8000 -i -#backchannel=1
+  play_pcm48k: exec:ffplay -fflags nobuffer -f s16be -ar 48000 -i -#backchannel=1
+```
+
 ## Backchannel
 
 - You can check audio card names in the **Go2rtc > WebUI > Add**