What is lossless compression? It is a way of making a file smaller so that the original can be rebuilt exactly when the file is opened again. Nothing is thrown away; the data is only stored more cleverly. FLAC for audio and ZIP for documents work this way.
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Files up to 2 GB · export to TXT, MD, DOCX, PDF, SRT and VTT · speaker labels and timestamps · about 30 languages
Key facts
- The saving depends on the content: speech with long pauses shrinks well, while dense noise leaves little to squeeze out and the file barely changes.
- Lossless audio stays much larger than a lossy copy of the same recording, because every detail of the signal is kept.
- A FLAC file decodes back to the same samples as the WAV it was made from, which is why archives and editors prefer it.
- Compressing and decompressing again and again does not wear the audio down, unlike repeated saving in a lossy format.
- For transcription the extra detail seldom matters, so lossless is mostly a choice for storage and editing.
What it looks like
// pack a recording without losing anything
ffmpeg -i talk.wav -c:a flac talk.flac
// unpack it again
ffmpeg -i talk.flac -c:a pcm_s16le back.wav
// the two checksums should match
ffmpeg -i talk.wav -map 0:a -f hash -hash md5 -
ffmpeg -i back.wav -map 0:a -f hash -hash md5 -
More
See the full list of languages, the tools and the glossary.
Frequently asked questions
What is the difference between lossless and lossy?
Lossless storage can be reversed to the exact original. Lossy storage removes some data for good, so the smaller file can never return to the source.
Does lossless audio give a better transcript?
Rarely by itself. A clear voice and little noise matter more. Lossless only helps when the alternative is a very heavily compressed lossy copy.
Is a ZIP archive lossless?
Yes. Unpacking a ZIP gives back every byte of the files that went in. The same idea is used for lossless audio, with methods tuned to sound.
Can I send a lossless file to the Potok bot?
The bot accepts audio files, also sent as a document, up to 2 GB. Larger files go through the Upload button in the bot's mini app.
How can I check that nothing was lost?
Decode the compressed file back to WAV and compare a checksum of the audio with the original. Matching checksums mean the two are identical.
Sources
Each source was opened by hand on the date shown. Pages change, so open the source if a detail matters to you.
- Lossless compression (Wikipedia), Wikipedia · checked
- FLAC (Wikipedia), Wikipedia · checked
Try it on your own recording
Send your voice message, audio or video to @potok_now_bot on Telegram and the text comes back in the chat.
Open @potok_now_bot in Telegram