I have more video music files than audio files on my iPhone. The simple reason is the added fun of watching both the video and enjoying the soothing music. 

There is a disadvantage though as there is no easy way to listen to only the audio content of these video files when you are on the go or simply to save the battery. And the other agony is the inability of the iPhone to auto play the videos one after the other. Hold on, there is a workaround to stream video files and also to listen to only the audio content. 

Here is what I did to lie to my iPhone.

1. I deleted all the video files in iTunes that I want to add to the selected list

2. Delete the same files on my iPhone

3. Add the files to iTunes again from my system preceded by one audio file

4. Connect the device to iTunes and select the files for syncing 

5. Sync the iPhone. 

Now, what happens here is like the video files would all be displayed in Recently Added section under Playlists tab. Make sure that the audio file is on the first list. 

Play the audio file and come out of the iPod application leaving the music on. You can lock the phone or go to other applications while the music video files are played one after the other. 

After this, the same list is auto added to Recently played section and then to the Top 25 Most Played section subsequently. The other feature that comes with this operation is that the device would play the videos one after the other when you watch the movie files.