Add 'linux/ffmpeg'

linux/ffmpeg

@@ -0,0 +1,16 @@
+ ## Duplicate DTS and encode AAC
+ ```
+ ffmpeg -y -i <input> -strict -2 -map 0 -c copy -map 0:a0 -c:a:1 aac -b:a 192k -ac 2 -f matroska <out>
+ ```
+
+  ## Attach Cover Art
+ ```
+ function addcover(){
+ ffmpeg -i $1.mkv -map 0 -c copy \
+        -attach $1-poster.jpg -metadata:s:t mimetype=image/jpeg -metadata:s:t filename=cover.jpg \
+        -attach $1-fanart.jpg -metadata:s:t mimetype=image/jpeg -metadata:s:t filename=fanart.jpg \
+        $1.plus.mkv
+ }
+ ```
+ Note: gerbera doesn't read the jpg. :(
+     Why?