Combining audio:
ffmpeg -f concat -safe 0 -i <(echo "file '$fn1'"; echo "file '$fn2'") -c copy $fn_out fn1 and fn2 can't be relative paths. Can use readlink -f to resolve any relative paths. Creating videos from images and audio:
for x in p*; do
out=$x/video.mp4
mp3=$(ls $x/*mp3)
cover=$x/cover.jpg

echo ffmpeg -loop 1 -framerate 2 -i $cover -i “$mp3” -c:v libx264 -preset medium -tune stillimage -crf 18 -c:a aac -b:a 192k -shortest -pix_fmt yuv420p -movflags +faststart $out
done

Upload
https://github.com/tokland/youtube-upload