Steps to reproduce:
1. Open the Upload Recording interface in 2 or more windows/tabs
2. Submit multiple uploads so that they are running concurrently. (I tested with a ~1GB mp4 file)
3. compare the md5 checksums for the resulting source video w/ the original, local file
Actual Results: checksums will not match and video will be glitchy or just un-encodable
Expected Results: checksums should match
The problem is the use of non-thread-safe read buffer defined at the class level in FileUploadServiceImpl.java. Fix is to simply create the read buffer each time within the FileUploadServiceImpl.acceptChunk scope.