Audio Codec filter
It seems that Video Codec Source can be set, but not the audio codec source.
In Video Codec Source you can have transcoding only for H264, and if already H264 it passes and does not transcode.
In Audo Codec source when audio is transcoded to AAC and it is passed to another tvheadend, the audio is transcoded again (AAC > AAC) and it does not passthrough.
transcode: 016E: 1:H264 > Passthrough
transcode: 016E: 2:AAC-LATM > AAC (aac) (it is already AAC and it should not retranscode).