Update readme about exec two way audio

README.md

@@ -217,6 +217,7 @@ Supported for sources:
 - [TP-Link Tapo](#source-tapo) cameras
 - [Hikvision ISAPI](#source-isapi) cameras
 - [Roborock vacuums](#source-roborock) models with cameras
+- [Exec](#source-exec) audio on server
 - [Any Browser](#incoming-browser) as IP-camera
 
 Two way audio can be used in browser with [WebRTC](#module-webrtc) technology. The browser will give access to the microphone only for HTTPS sites ([read more](https://stackoverflow.com/questions/52759992/how-to-access-camera-and-microphone-in-chrome-without-https)).
@@ -407,26 +408,30 @@ Exec source can run any external application and expect data from it. Two transp
 
 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**.
+**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 your own software
 
-Pipe commands support two parameters (format: `exec:{command}#{param1}#{param2}`):
+Pipe commands support parameters (format: `exec:{command}#{param1}#{param2}`):
 
 - `killsignal` - signal which will be send to stop the process (numeric form)
 - `killtimeout` - time in seconds for forced termination with sigkill
+- `backchannel` - enable backchannel for two-way audio
 
 ```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 -
   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
 ```
 
 #### Source: Echo