How to compress audio for transcription

Method 1 — Extract audio from a video file

If you have a video file (MP4, WEBM, MOV) that's mostly speech, the audio track is usually 5–10× smaller than the video. Mictoo only needs the audio — the video doesn't help transcription. This is the fastest fix for most users.

Online (no install)

• Convertio — drag MP4, choose MP3 or M4A, download.
• CloudConvert — supports MP4 → MP3 / M4A / WAV.
• Media.io — fast in-browser conversion.

Command line (ffmpeg)

ffmpeg -i input.mp4 -vn -acodec copy output.m4a

-vn strips video, -acodec copy keeps the audio quality intact. Fast — no re-encoding.

Method 2 — Lower the audio bitrate

Most podcasts and meetings are recorded at 128–192 kbps. For transcription, 64 kbps mono is more than enough — accuracy stays the same and the file becomes 2–3× smaller. This is the best method for long audio files.

Online

• Online Audio Converter — set quality slider to 64 kbps, mono.
• FreeConvert Audio Compressor — choose target size.

Command line (ffmpeg)

ffmpeg -i input.mp3 -ac 1 -b:a 64k output.mp3

-ac 1 converts to mono (speech is fine in mono),-b:a 64k sets audio bitrate to 64 kbps.

Rough math: 64 kbps gives ~28 MB per hour. A 1-hour interview fits in roughly 28 MB — close to the limit. Drop to -b:a 48k for ~21 MB/hour without noticeable accuracy loss.

Method 3 — Split into shorter parts

If you need to keep the original quality (legal, medical, archival), split the file into chunks of 20–25 minutes and transcribe each separately. Then join the transcripts in any text editor.

Online

• mp3cut.net — drag MP3, set start/end, download.
• Clideo Cut Audio — clean UI, supports most formats.

Command line (ffmpeg)

ffmpeg -i input.mp3 -f segment -segment_time 1200 -c copy part_%03d.mp3

Splits the input into 20-minute (1200 seconds) parts named part_001.mp3, part_002.mp3, etc. Then upload each to Mictoo.