Is there any way to convert from gtfs real time feed (service alerts) to .pb (protocol bufers) file.
Sample service alerts file : https://developers.google.com/transit/gtfs-realtime/examples/alerts
I think you might be confused.
GTFS-Realtime is typically encoded in Protocol Buffers format-- which is designed for efficient machine to machine communication. This is not human readable, so many servers include a human readable version.
Since you didn't give enough detail for the source, I can't give a specific answer, but you may need to specify a format in the GET parameters or in the request headers to receive protobuf.