Mine
public text v1 · immutable$ echo xx__SRCxxx | sed "s/__SRC/ ` echo ./yuv/foreman-qcif.yuv | sed 's/\./\\\./g;s/\//\\\//g' ` /g"
sed: -e expression #1, char 20: unknown option to `s'
xx xxx
$ $ echo xx__SRCxxx | sed "s/__SRC/ ` echo ./yuv/foreman-qcif.yuv | sed 's/\./\\\./g;s/\//\\\//g' ` /g"
sed: -e expression #1, char 20: unknown option to `s'
xx xxx
$