Trying to Batch Merge MP3 Audio and MP4 Video files

This is what I got so far…

for %%a in (“.mp4″) do _ffmpeg -i (“.mp3″) -c copy “__newfiles%%~na.mp4”

But doesnt quite work…

ffmpeg -i video.mp4 -i audio.wav -c copy output.mkv

Trying to modify the above which merges audio/video without reencoding

Ive got about 2000 files to do. Any help would be great, thank you!