# This uses ffmpeg https://www.ffmpeg.org/
# modify the video and audio extensions if needed

mkdir -p output

foreach ($video in (ls *.mp4)) {
    $video_name = ($video).Name;
    $audio_name = $video_name.replace('.mp4', '.mp3');
 
    ffmpeg -i $video_name -i $audio_name -c copy -map 0:v:0 -map 1:a:0 "output/$video_name"
    # the above is based on https://superuser.com/a/1137613/1006010
    # If the audio is longer than the video, you will want to add -shortest before the output file name.

    # Using -c:v copy instead of -c copy means to copy the video only, and re-encoding the audio. -c copy will copy both the video and audio without re-encoding.
    # -map 0:v:0 maps the first (index 0) video stream from the input to the first (index 0) video stream in the output.
    # -map 1:a:0 maps the second (index 1) audio stream from the input to the first (index 0) audio stream in the output.
    # Not specifying an audio codec, will automatically select a working one. You can specify one by for example adding -c:a libvorbis after -c:v copy. You can also use -c copy to avoid re-encoding the audio, but this has lead to compatibility and synchronization problems in my past.
}