[Split out from non-LRC related thread]
Thanks for the detailed response,
I've actually done tons of research and testing about embedding LRC lyrics (which is always synced) into mp3. Embedding LRC lyrics into USLT frame of ID3v2 tag does work for some players (e.g. MusicBee, foobar2000(with ESLyric / Lyrics Show Panel 3 plugin), WMP(with MiniLyrics), Musicolet, etc.), but it's still not as widely-supported as the seperate .lrc file, mainly because the USLT frame is technically intended for Unsychronised (instead of synced) Lyrics according to ID3v2 standard.
In fact, besides embedding LRC lyrics into USLT frame, there're no better way of embedding LRC lyrics into mp3 (based on my research and testing) :
The SYLT frame of ID3v2 tag is for synchronised lyrics, but it uses a different format than LRC, and support for SYLT frame is rare to find (the only program I know that supports SYLT are: MusicBee, MiniLyrics, JetAudio).
You can create a custom TXXX frame (of ID3v2 tag) and name it "LYRICS", but support for that is also very rare (from what I know, only MusicBee, foobar2000(with ESLyric / Lyrics Show Panel 3 plugin), and WMP(with MiniLyrics) supports that).
The Lyrics3v2 tag doesn't even support Unicode.
Therefore, there're no standard and also widely-supported way of embedding LRC lyrics into mp3, the best I can do is importing it into an USLT frame, which is still not as standard as a seperate .lrc file.
By the way, is support for embedded LRC format lyrics in the USLT frame a planned feature of Poweramp? (Max said "synced/non-synced lyrics + .lrc support" but I don't know if and how he plan to implement embedded synced lyrics, I hope it's the "embedded LRC format lyrics in the USLT frame" way which is probably the most common.)