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How to Convert MP4 to MP3 (Extract Audio from Video)

You have a video but you only need the audio — a podcast episode, a lecture, a music video, a voice memo recorded as video. Here's how to extract it in seconds.

Why extract audio from video?

Common reasons people convert MP4 to MP3:

• Save a podcast or interview that was only posted as video
• Extract the audio from a music video for offline listening
• Pull voice from a video recording for transcription
• Reduce file size when you don't need the visual component (a 100MB video becomes a 5MB audio file)
• Create audio clips from screen recordings or presentations

The privacy problem with online converters

Most "MP4 to MP3" search results lead to websites where you upload your video file. If it's a personal voice memo, a private lecture, or client content, that's a privacy risk you don't need to take. Converting locally takes the same amount of time and keeps your files on your machine.

Converting with ConvX

Basic extraction

convx convert video.mp4 --to mp3

Extracts the audio track and encodes it as MP3. Default quality is 192kbps, which is transparent for speech and good for music.

High quality for music

convx convert video.mp4 --to mp3 -q 95

Quality 95 maps to 320kbps MP3, the highest standard bitrate. Use this when audio quality is critical.

Convert to other audio formats

convx convert video.mp4 --to flac    # lossless
convx convert video.mp4 --to aac     # smaller than MP3
convx convert video.mp4 --to opus    # best compression
convx convert video.mp4 --to wav     # uncompressed

Batch extract from multiple videos

convx convert "./lectures/*.mp4" --to mp3 -j 4 -d ./audio

Extracts audio from every MP4 in the lectures folder using 4 parallel jobs.

Using the desktop app

Drag your video into ConvX, select MP3 (or any audio format) as the output, adjust the quality slider if needed, and click convert. The app shows the estimated output size before you start.

MP3 vs AAC vs FLAC: which audio format?

• MP3: Universal compatibility. Every device and player supports it. Good default choice.
• AAC: Better quality than MP3 at the same bitrate. Supported by all modern devices. Slightly smaller files.
• FLAC: Lossless compression. Perfect audio quality but 3-5x larger files. Use for archival or when quality is paramount.
• Opus: Best compression ratio of any modern codec. Great for voice. Not universally supported on older devices.

Does conversion lose quality?

MP4 video already stores audio in a compressed format (usually AAC). Converting to MP3 is a transcode — decoding the original and re-encoding. This is technically a generational loss, but at 192kbps or higher, the difference is inaudible to virtually everyone. If you need perfect quality, convert to FLAC instead.