Why so many of your files are secretly AAC
AAC is less a file you download than a codec you end up with. Apple built it into iTunes and the iPhone, YouTube serves it on most audio streams, and broadcasters use it for digital radio. The extension you see is often .m4a or .mp4 rather than .aac, because AAC is the audio living inside those containers.
That naming confusion trips people up when they try to transcribe. A file named .m4a and a file named .aac frequently hold identical audio, and a tool that only advertises one of them can look like the wrong choice. FastScribe reads the audio stream regardless of which extension the container carries.
What AAC compression means for accuracy
AAC is lossy, meaning it discards detail that most listeners will not notice in order to make the file smaller. At the bitrates streaming services and phones use, it holds speech noticeably better than MP3 at the same size, because the codec was designed several years later with speech and music both in mind.
In practice this makes AAC one of the easier formats to transcribe accurately. What limits your result is almost never the codec; it is how far the microphone sat from the speaker and whether two people talked over each other. A clean AAC recording transcribes about as well as an uncompressed original.
Frequently asked questions
Is AAC the same thing as M4A?
Not quite. AAC is the codec that compresses the sound; M4A is a container file that usually holds AAC audio inside it. Both work here, and you do not need to rename or convert anything before uploading.
Can I transcribe AAC audio pulled from a video?
Yes, and you can also upload the video itself and let us take the audio out. Extracting the AAC track first is only worth doing when you want a much smaller file to upload over a slow connection.
Does the bitrate of my AAC file change the result?
Only at the extremes. Anything from about 96 kbps upward transcribes essentially the same. Very low bitrate files, the kind produced by old voice apps trying to save space, lose consonant detail and will read slightly rougher.