ffmpeg - warnings when i try to merge several audio files with an .mp4 file
The first warning means one of the WAV inputs has no channel layout defined i.e. channel 1 is Front Left, channel 2 is Front Center..etc. amerge decides the channel layout of the output stream based on the input, but since that designation is missing for one of the inputs, amerge will assign a channel layout which is default for the number of channels present in the output.

One thing you could try is rewrap all of the audio inputs i.e.

ffmpeg -i audio1.wav -c copy audio1-new.wav




The 2nd warning is displayed whenever VBR mode is invoked. Unless you get the error: Unable to set the VBR bitrate mode, you should be fine.