MP4 or MP3: which format should you save a video in?

Every download screen asks the same question: do you want the video file or just the sound? The answer depends less on quality and more on how you intend to use the file afterwards. This guide compares the two and gives you a simple rule you can reuse.

What MP4 gives you

MP4 is a container that holds both a video track and an audio track. It plays on virtually every phone, TV, browser and editing app without conversion, which is why it is the default for saved videos.

• Keeps the picture, subtitles burned into the frame and any on-screen text
• Needed if you plan to re-edit, crop or reuse footage you own
• Plays everywhere, from old televisions to the newest phones
• Larger files: a few minutes of 1080p can be several hundred megabytes

What MP3 gives you

MP3 keeps only the audio track. For interviews, lectures, podcasts republished as video, or a track you own the rights to, it is dramatically smaller and works in any music player.

• Typically 5 to 15 percent of the size of the same clip in MP4
• Plays in car stereos and offline music apps that reject video files
• Uses less battery to play because there is no video to decode
• No way to recover the picture later, so download MP4 too if you might need it

MP3, M4A and AAC: what you actually receive

Many platforms store the sound of a video as AAC, usually inside an M4A or MP4 container, rather than as MP3. A downloader that hands you the original audio track without conversion gives you the best quality, even if the file name or label says MP3. Converting one lossy format to another loses a little more detail each time, so convert only if a device genuinely needs MP3.

File size examples

A ten-minute talk at 720p might be around 300 to 500 megabytes as video, and around 10 to 20 megabytes as audio. Over a month of commuting that difference decides whether your phone has space for anything else. For a lecture series, audio-only can turn gigabytes into a few hundred megabytes.

A simple rule

If you will ever look at the file, choose MP4. If you will only listen to it, choose audio. When storage is not a problem, saving both takes one extra tap and removes the guesswork.

Rights still apply to audio

Taking only the sound does not change who owns it. Music, voice-overs and sound effects are protected like the picture. Keep audio you recorded, audio under an open licence, or audio the owner has allowed you to keep. Read our guides to responsible downloading and to Creative Commons for what is acceptable.

Related guides

If you are unsure about resolution labels, read what 360p, 720p and 1080p mean. If your file is silent, read why some downloads have no sound. And for a bitrate explanation for speech and music, see the audio bitrates guide.