Our new music matching feature gets your songs into your online music library on Google Play much faster. We’ll scan your collection and quickly rebuild it in the cloud – all for free. And we’ll stream your music back to you at up to 320 kbps.
So what does that actually mean though? Well, your original music files can’t be uploaded to your Google Music account unless the servers can’t find your music. So if you have some obscure non published mainstream CD sitting around that you love to pieces, it won’t upload. This is actually a very good thing. What the scan and match service will do is scan the files you want to upload and then pull the 320kbps version and toss it in your Google Music account for you. This saves OODLES of bandwidth and upload time.
As for current Google Music users, we found out some information from Google Support thanks to Hans Hong . You won’t need to do anything to take advantage of the service. We mean, you don’t need to delete your library and reupload to get your songs matched. Google will be handling this for us all over the next few months and automatically match anything they can in your existing library. Also, anything they match WILL count towards your 20,000 track limit.
At least, that is how I understand it. If I am wrong, please feel free to correct me in the comments.
Source: Google+ via Android Police