The use-case issue here is what to do with users who add large audio files to their Bloom book?
It is probably not reasonable to expect a typical native speaker “Bloom book creator” to be savvy enough to know how convert and compress their audio files ahead of time so they are ready to be imported into Bloom. Rather, what is needed is an automatic process built into Bloom which converts any imported audio to MP3 format with an appropriated compression (either a default setting, or, if selected, a user-specified bit rate).
This way a user focuses on finding the audio, music, etc, and just imports it. Bloom handles the processing to “get it reasonable” for Bloom eBooks.
WAV files are uncompressed and thus recreate the audio as clear as possible but are huge.
- WAV files generally run 10x the length (2 minutes = 20MB)
- FLAC is a loss-less compression format that runs around 6x the length (2 minutes = 13MB)
These two formats (WAV and FLAC) should probably not be stored in Bloom books.
There are also several other formats like AIFF, PCM, AAC, WMA, and OGG, but MP3 format is preferred as it can be a much smaller format (though “lossy”). But how small varies with the chosen compression/bit rate:
MP3 at 256kps runs 2x the length (2 minutes = 4MB)
MP3 at 192kps runs ~1.5x (2 minutes = 3MB)
MP3 at 128kps runs <1x (2 minutes < 2MB)
MP3 at 96kps runs 0.7x (2 minutes = 1.4MB)
MP3 at 64kps runs ~0.5x (2 minutes = 1MB)
(These are all approximate)
Some popular apps like YouVersion and FCBH compress their audio down to 64kps or lower. But honestly the distortion and compression artifacts are noticeable at these levels, and this becomes distracting to listeners, especially if they use headphones.
My personal preference is going no lower than 96kps. I much prefer 128kps for speech/reading and 192kps for music. So, for this reason, it would be ideal if Bloom had a default setting (say 96kps), but allowed the user to specify a preferred bitrate, in case they want more fidelity or need even smaller files than 96kps,