How to turn an MP3 into an MP4
- Drop the MP3 (or M4A, WAV, FLAC, OGG) on the left.
- Drop the cover art or a photo on the right. You can skip this and get a plain background.
- Choose the shape: YouTube (16:9), Square or Shorts, Reels, TikTok (9:16). The preview shows exactly what the video will look like.
- Press Make the MP4 and download it.
The line under the settings says what will happen to your sound before you start: copied as it is, or converted, and why. When the video is ready, the page reads it back and shows what is inside it.
Your sound goes in unchanged
An MP4 file can carry MP3 and AAC sound as they are. So instead of decoding your song and compressing it a second time, which is what most converters do and which costs a little quality each time, this tool copies the sound into the new file untouched. Afterwards it compares every sound packet in the MP4 with your original, byte for byte, and shows the count. Formats an MP4 can’t carry (WAV, FLAC, OGG, Opus) are converted once, to AAC at 192 kbps, which is above what YouTube streams.
The video is also exactly as long as the sound. Some tools round the picture up to a whole number of frames or stop at the shorter of the two, which leaves a second of silence at the end or cuts the last note. Here the last frame is shortened to end with the audio.
Why a still picture does not need 30 frames a second
Most converters write 25 or 30 identical frames for every second of the song. We measured what that costs, using a 1920 × 1080 photo and a 3-minute MP3 in Chrome on a Windows PC (18 October 2026), and read each result with a separate decoder (PyAV):
| Setting | Time to make | Picture part of the file | Whole MP4 |
|---|---|---|---|
| 30 fps, a key frame every 2 s (typical converter) | 32 s | 6.5 MB | 10.9 MB |
| 1 fps, a key frame every 2 s | 1.8 s | 7.9 MB | 12.2 MB |
| 1 fps, a key frame every 10 s | 1.9 s | 1.9 MB | 6.2 MB |
| This page: 2 fps, a key frame every 10 s | 3.4 s, including the check | 1.9 MB | 6.2 MB |
Two things stand out. Cutting the frame rate makes the video about 17 times faster to produce, but on its own it does not make the file smaller: what fills a still-picture video is the key frames, the full pictures the video repeats so players can jump to any point. Spacing those out is what shrinks it. And the picture looked the same in all of them: the first and last frames scored the same against the original photo (35.2 dB PSNR at 30 fps, 35.3 dB at 1 fps). This page uses 2 frames a second with a key frame every 10 seconds, so seeking still lands quickly. Choose 30 fps for Instagram, whose Reels and Stories accept only 23 to 60 frames a second.
Fitting the picture
- Whole picture, blurred edges (the default): the picture is shown complete, and the empty space around it is filled with a blurred, darker copy of itself. A square album cover in a 16:9 YouTube video gets soft colour on both sides instead of black bars.
- Whole picture, plain edges: the same, with a solid colour you choose around it.
- Fill the frame: the picture is enlarged until it covers the whole video, and whatever sticks out is cut off. Good for wide photos in a 16:9 video; for an album cover in a vertical video it cuts a lot.
- The picture’s own shape: the video takes the picture’s proportions, up to 1920 pixels on the long side, with nothing added.
Photos from a phone are turned upright using the rotation saved in the file. iPhone HEIC photos need converting first, with HEIC to JPG, because most browsers can’t open them.
Uploading it
YouTube: the 16:9 MP4 uploads as a normal video. If the sound is a commercial recording, YouTube’s Content ID may claim it or block it in some countries; your own music, a podcast or a recording you have rights to is fine. Shorts must be vertical or square and, since 2024, up to 3 minutes long; trim longer audio first with Trim Audio. Instagram and TikTok: choose 9:16, 30 fps and AAC sound.
Related: to put music on a video you already have, use Add Music to Video; to get the MP3 back out of a video, MP4 to MP3; to make a quiet recording louder first, Increase Audio Volume. Everything runs in your browser: neither the sound nor the picture is uploaded.