Videos with multiple audio channels are common in the media industry. If you want to merge all the audio tracks in the master file and make a single track in the proxy you can use the below FFmpeg parameters.
-i
"eSourceFile" -filter_complex
"[0:1][0:2][0:3][0:4][0:5][0:6][0:7][0:8][0:9][0:10]
amix=inputs=10:duration=longest" -y -s 1280x720 -b:v 1024k -vcodec
libx264 -r eSourceFrameRate -movflags faststart -pix_fmt yuv420p
"eVideoProxy"
The above parameter is for a
video which is having 10 audio tracks. If your video is having a
different track number you can alter the parameter.
For example,
If the video is having only 6 tracks then it will be like,
-i
"eSourceFile" -filter_complex "[0:1][0:2][0:3][0:4][0:5][0:6]
amix=inputs=6:duration=longest" -y -s 640x360 -b:v 1024k -vcodec libx264
-r eSourceFrameRate -movflags faststart -pix_fmt yuv420p "eVideoProxy"
You can always refer ffmpeg
forum for any further information.