AAC Encoder Improvements

by Rostislav Pehlivanov for FFmpeg

Currently, the ffmpeg project hosts an incomplete implementation of an AAC encoder. This encoder has features missing, along with being lower quality than alternative free and non-free implementations. To be able to compete with such implementations of the AAC format, there are features that need to be implemented: perceptual noise substitution, intensity stereo, and others. The aim is to implement these features inside ffmpeg's AAC encoder such that eventually it could be considered stable.