The sequential playlist is the simplest form of playlists in SMIL.
In a sequential playlist, media objects are played in the order they are listed in the SMIL playlist. One media object starts playing after the preceeding one ends.
Simple loop
<seq repeatCount="indefinite">
<video src="ad1.mpg" region="main"/>
<video src="ad2.mpg" region="main"/>
<img src="ad3.png" dur="5s" region="main"/>
</seq>
Loop 2 videos and 1 JPEG indefinitely.
Nested loop
<seq repeatCount="indefinite">
<video src="ad1.mpg" region="main"/>
<seq repeatCount="2">
<video src="ad2.mpg" region="main"/>
<img src="ad3.png" dur="5s" region="main"/>
</seq>
</seq>
Plays the sequence: ad1, ad2, ad3, ad2, ad3 and repeats the entire sequence endlessly.
Source: a-smil.org