I wonder why it always re-cache a mp3 while already already cached half of it.

[jksniper]

I noticed that when I played a mp3, before it's fully cached, close the app. When reopen it, play the same mp3, the half cached file will be removed from disk and cache from the begining again. So if there is a way to recognise the cached part and just play local half cached files until it really needs to buffer more? So this can save more bandwidth of the server and also more smooth for users.
Thanks for your support.