Correct - seems to really only prefer mp4. About half of my library is not compatible. Fortunately a re-download isn't so bad, especially if it's an opportunity

Correct - seems to really only prefer mp4. About half of my library is not compatible. Fortunately a re-download isn't so bad, especially if it's an opportunity to get a higher resolution version (that's the optimist in me speaking). There are other VLC-like players available, but the drawback is the video must stream from your iOS device rather than the NAS.