Every Android device manufacturer has a customized version of the Android operating system, and in many cases they attempt to "optimize" the operating system to reduce battery usage. Unfortunately, this can sometimes cause the device to terminate audio that's playing in the background through the Chrome browser after a period of time, because the operating system incorrectly considers the background task (in this case playing our audio) as unimportant.
Please see this site
and locate the suggestions for your phone's manufacturer.
If you have a Samsung device, the instructions in this article
are easier to follow.