When I play certain MP3 files (such as lessons from JapanesePod101.com) on my iPod Touch, lyrics or transcripts that are embedded in the MP3 files are displayed in the media player.
I find this to be an extremely useful feature, and I believe I'm not alone. Despite that, neither the stock Android media player nor any other media player I've downloaded from the Market seems to support this. I just have not been able to find any way to get feature on my Nexus One.
This feature is important enough to me that I'm considering learning Android development just so I can write a simple media player that displays embedded lyrics or notes. However, the fact that nobody else seems to have done this makes me wonder - is it even possible? Is there something in the Android architecture or APIs that make it difficult or impossible to read and display lyrics information from MP3 files?