Disk Streaming of Compressed Audio Files

[drowaudio]

Motivation

When playing back compressed audio files, reading of the files takes much longer than using the existing memory mapped WAV file method. The juce::BufferingAudioSource method used for compressed files doesn't really form a suitable solution.
This is especially evident when jumping to a new position, dropouts are almost always heard.

Requirements

• Real-time safe read operations which don't block at all (this causes dropouts in the main audio graph)
• Error reporting for when a read operation fails so audio can be faded in/out accordingly to avoid glitches
• Ability to cache the whole decompressed file in memory
• Better handling of caching, keeping most recently used blocks. This will much improve the audio thumbnail drawing where views tend to be scrolled backwards and forwards rather than being completely random access

Approach

• Replace the fallbackReader (and internals of CacheAudioFormatReader) with a better juce::AudioFormatReader subclass
• This should still use a thread to read the audio file and copy it in to memory
• Memory should be allocated in blocks covering a portion of the audio file
• If the whole file is to be cached, the thread should fill these blocks but this may happen out of order if the read position is changed
• Allocated blocks should be contiguous for better cache performance
• Blocks should be time-stamped and the oldest ones reused to keep recently used blocks in memory
• Some file types (mp3?) may need to read contiguously to avoid sample mismatches?
• It might be an idea to use a shared allocator for this so all cache blocks are near each other in memory
• There might be a performance boost by memory mapping the original file and letting the OS cache the file reads
• This should be developed with benchmarks and tests to ensure performance is as desired