How does an iPhone know which mp3s are podcasts?
Solution 1:
I think that the way that iTunes separates out podcasts in the Library has to do with how podcasts are synced. Podcast are handled differently than Mp3s.
I just dug into the iTunes Music Library.xml and saw that on podcasts, the following elements appear under podcasts
<key>Podcast</key><true/>
So it has to to with the fact that iTunes flags podcasts as such, and know to handle them differently.
UPDATE: Also, its more than just that key-value pair on the podcast entry, because if you add that key-value pair to any song, it gets removed by iTunes when you close it
UPDATE 2: I also found the entry specifying the Podcast "playlist"
<dict>
<key>Name</key><string>Podcasts</string>
<key>Playlist ID</key><integer>11896</integer>
<key>Playlist Persistent ID</key><string>6D71FCACB79A978D</string>
<key>Distinguished Kind</key><integer>10</integer>
<key>Podcasts</key><true/>
<key>All Items</key><true/>
<key>Playlist Items</key>
<array>
<dict>
<key>Track ID</key><integer>7194</integer>
</dict>
<dict>
<key>Track ID</key><integer>7192</integer>
</dict>
<dict>
<key>Track ID</key><integer>7190</integer>
</dict>
</array>
</dict>
Long story short, iTunes is doing a lot of work in the background!!
Solution 2:
There is a handy free Applescript from Doug's Scripts that will re-add the selected tracks as podcasts.
Re-Add Selected Tracks as Podcast v1.2
Solution 3:
A quick look through my iTunes library shows that most Podcasts have the ID3 genre attribute set to... "Podcast"