You need to compare apples with apples.
You don't say what the original AC3 files are. Most commercial AC3 encodings are very generous bit-rate wise, so there is lots of fat for neroaacenc to trim, hence a high apparent efficiency in your trancode.
I think what you are actually measuring is how efficiently compressed the original AC3's were. If the original bit-rate was over generous then you get a big win. If the original bit-rate was a little squeezed then then you gain less.
|