PubToo · Guides
Audio compression formats: AAC, ALAC and FLAC explained
Choose AAC, ALAC or FLAC for sharing, playback or keeping a lossless source. Understand M4A containers, conversion limits and how to check an audio export.
Decide whether the audio file is for sharing, everyday playback or keeping a high quality source. Renaming its extension does not convert it. Converting an existing lossy recording to a lossless format cannot restore information already removed.
PubToo reads MP3, M4A, AAC, WAV, FLAC, Opus and other supported audio on your device. It exports AAC/M4A, ALAC/M4A or FLAC. MP3 is supported as an input, but there is no MP3 export.
1. For sharing and everyday playback, check AAC
AAC is a lossy codec that trades some audio information for a smaller file. PubToo defaults to AAC/M4A at 160 kbps for stereo and 80 kbps for mono. Actual size also depends on duration and the encoding result.
M4A is a container that can hold AAC or ALAC. When a receiving platform says it accepts M4A, check whether it supports the codec inside the file as well.
2. For a lossless source, compare ALAC and FLAC
ALAC and FLAC use lossless compression. When the source and export path support it, they can store compressed audio without discarding information through lossy coding. Their file sizes usually differ from an AAC sharing copy.
Choose ALAC/M4A or FLAC according to the receiving player. Neither improves the original quality of an existing MP3 or AAC recording, and neither guarantees a smaller file than the input. Avoid converting again simply to change an extension.
3. Read source limitations and format prompts
The source, channel count and device capabilities limit available exports. PubToo suggests a viable format when the selected lossless path is unavailable or the channel count exceeds AAC capabilities. It fails explicitly if no supported path is available.
Keep the original and export for the task at hand. If you need to retain the original bytes, archive the source file; audio transcoding does not replace keeping that original.
4. Listen and verify the exported file
Compare actual size and duration. Listen to the start, ending and important passages, checking for gaps, distortion or channel problems. Open the result in the receiving player before sharing or archiving it.
If it still needs to be smaller, review the accepted codec, the actual size limit and whether a lossless copy is essential. Current platform requirements and supported formats are listed on PubToo’s support page.