1. Create file for exmpl/home/hts/.hts/tvheadend/scripts/pip with next code:

version with channel numbers


#!/bin/bash
ffmpeg -loglevel fatal -thread_queue_size 512 -i http://127.0.0.1:9981/stream/channelnumber/$1 -thread_queue_size 512 -i http://127.0.0.1:9981/stream/channelnumber/$2 -filter_complex "[1]scale=iw/3:ih/3 [pip]; [0][pip] overlay=main_w-overlay_w-10:main_h-overlay_h-10[v]" -map "[v]" -map 0:1 -map 1:1 -metadata:s:a:0 language=bul -metadata:s:a:1 language=eng -strict -2 -ac 2 -ar 44100 -vcodec libx264 -q:v 5 -crf 5 -r 25 -acodec aac -metadata service_provider=PiP -metadata service_name=PiP -tune zerolatency -f mpegts pipe:1

version with channelID


#!/bin/bash
ffmpeg -loglevel fatal -thread_queue_size 512 -i http://127.0.0.1:9981/stream//id//$1 -thread_queue_size 512 -i http://127.0.0.1:9981/stream//id//$2 -filter_complex "[1]scale=iw/3:ih/3 [pip]; [0][pip] overlay=main_w-overlay_w-10:main_h-overlay_h-10[v]" -map "[v]" -map 0:1 -map 1:1 -metadata:s:a:0 language=bul -metadata:s:a:1 language=eng -strict -2 -ac 2 -ar 44100 -vcodec libx264 -q:v 5 -crf 5 -r 25 -acodec aac -metadata service_provider=PiP -metadata service_name=PiP -tune zerolatency -f mpegts pipe:1

NOTE: that's onliners keep in mind !

2. Add MUX, URL field:


pipe:////home/hts/.hts/tvheadend/scripts/pip 102 103

https://s22.postimg.cc/yio4l6v4x/download.png
or

pipe:////home/hts/.hts/tvheadend/scripts/pip BBC NBS

First channel number/id is main (on full screen) second is in small window.

IMPORTANT: MarkRespawn option

3. Map MUX as service and vice versa

That way connection to two channels will be open only when the PiP channel is requested (not unnecessary provider connections)

OPTIONAL: If you want to make audio interchangeable in KODI could made it by Keyboard.xml


      <!-- PVR windows -->
      <e>ActivateWindow(TVGuide)</e>
      <h>ActivateWindow(TVChannels)</h>
      <j>ActivateWindow(RadioChannels)</j>
      <k>ActivateWindow(TVRecordings)</k>
      <b>ActivateWindow(TVTimers)</b>
      <l>AudioNextLanguage</l>

That way you could switch languages with key L