mpv shell script. Prepends first arg on each line of stdin, then launches mpv with resulting playlist. Uses neat trick with file descriptors and unlinked files.

mpv-from

#!/bin/sh
trap 'printf "(exit) mpv-from\n" >&2' EXIT

usage () {
        printf '(usage) mpv-from <basepath> [mpv-args]\n'
}

test $# -ge 1 || {
        printf '(error) not enough arguments\n' >&2
        usage >&2
        exit 127
}
_basepath="$1" ; shift

_pipe="$(mktemp)" \
&&      exec 3<>"$_pipe" \
|| {
        _ec=$?
        printf '(error) can\047t open file descriptor\n' >&2
        exit $_ec
}
rm "$_pipe"

awk -v _base="$_basepath" '{print _base $0}' >&3
printf '(info) exec mpv\n' >&2
# can't use fd:// because of bug that prepends 'fd://' to files in playlist if there is no protocol ('file://' protocol not helping)
exec mpv --playlist=- "$@" <&3