Why turn an MP3 into an MP4?

YouTube and most video platforms only accept video files. If you have an MP3 (music, podcast, voiceover) and want to upload it, you need to wrap the audio in a video container with at least one visual track — usually a still image or thumbnail. This tool does exactly that.

Is this free? Does my audio get uploaded?

Free, no sign-up, no usage limit. Everything runs in your browser — your audio and image never get uploaded to any server.

How long does the conversion take?

First time loads the in-browser encoder (~25 MB, ~10–20 seconds). After that, encoding is near-instant for a still cover image, whatever the audio length.

What's the output quality?

H.264 video (libx264) at 720p or 1080p with the still-image preset, plus AAC audio at 192 kbps. The video looks crisp because it's a single still frame held for the full duration — no compression artifacts from motion.

Free MP3 to MP4 Converter

Turn any audio file (MP3, WAV, FLAC, M4A, OGG, AAC) into an MP4 video — perfect for uploading audio to YouTube, Instagram, or anywhere that needs video. Add your own cover image or use our generated default. 100% in your browser. Files never leave your device, no sign-up.

100% in your browser. Everything encodes locally — your audio and image files never leave your device. The first conversion loads the encoder (~25 MB, ~10–20 seconds); after that, every encode is instant. Privacy policy.

No file handy?

Drop an audio file

or click to browse. MP3 is most common.

MP3WAVOGGFLACAACM4A

audio.mp3

—

♫

Default cover (auto-generated)

A dark gradient with the filename and music-note icon. Or upload your own JPG/PNG (square or 16:9 works best for YouTube).

Resolution: Output: MP4 · H.264 video + AAC 192 kbps audio

✨ Do you want to add subtitles to your video?

✨

Add auto-subtitles to your video

Subtitles are auto-transcribed from the audio. Works best on spoken audio (podcasts, voiceovers, narration) — results may be poor on music or instrumentals.

	Free — in your browser	Pro — in the cloud
Accuracy	Fast / balanced model	Highest accuracy (large-v3)
Speed	Runs on your device — slower on long files	Done in seconds
Punctuation & names	Basic	Accurate — casing, names, numbers
Privacy	100% on your device	Encrypted upload, then auto-deleted
Price	Free, always	From a few cents an hour
		Get Pro

Caption style

Font size Text color Highlight color

Live preview (captions appear as the audio transcribes)

Why convert MP3 to MP4 — common use cases

Upload a song or podcast to YouTube. YouTube doesn't accept MP3 files directly — only video. Wrap your audio in an MP4 with a still cover image and you can upload it like any other video.
Share on Instagram, TikTok, X, LinkedIn. Same constraint as YouTube — these platforms require video files for the audio-heavy formats (carousel posts, story audio, etc.).
Background audio for video editors. Some editors prefer importing audio as MP4 to keep all assets in one container format.
Quick visual layer for voice memos. Turn a voice note + a screenshot or photo into a shareable MP4 in 10 seconds.

How this tool works (100% private, in your browser)

Behind the scenes, a powerful encoder runs entirely in your browser (compiled to WebAssembly). When you click Convert to MP4, your browser combines the audio track with the still image into a single MP4 file using the H.264 video codec and AAC audio codec. Because it all runs locally on your machine, your audio and cover image are never uploaded to a server. We literally cannot access what you're converting.

Output specifications

Container: MP4 (with +faststart flag for streaming-friendly playback)
Video codec: H.264 (libx264), still-image tune, ultrafast preset for browser speed
Audio codec: AAC at 192 kbps (near-CD quality, broadly compatible)
Pixel format: yuv420p — required for YouTube and most platforms
Resolution: Your choice — 1080p or 720p
Frame rate: Still image (efficient encoding)

Tips for YouTube uploads

Pick a square or 16:9 cover image. YouTube's default video aspect ratio is 16:9. A square image will get letterboxed but still works.
Make the cover image high-resolution. A 1920×1080 (or larger) cover image will look crisp; small images get upscaled and look blurry.
Add chapters in YouTube Studio. Use timestamps in your description to break up a long audio file.
Use 1080p output. YouTube treats 1080p as HD; lower resolutions can affect recommendation.

Frequently asked questions

Is this really free? Does my audio get uploaded?▼

Free, no sign-up, no usage limit. Everything runs in your browser. Your audio and cover image never get uploaded to any server.

What audio formats can I use as input?▼

MP3, WAV, OGG, FLAC, AAC, M4A, and most other formats your browser can decode. Output is always MP4 for broad compatibility.

What if I don't have a cover image?▼

We generate a default — a dark gradient with the filename and a music-note icon. Works for podcasts, voice memos, and quick uploads where the visual isn't the focus.

Why is the first conversion slower than the next ones?▼

The in-browser encoder loads on first use (a ~25 MB module that downloads once per browser session). After that, conversions are fast — no reload needed.

Is there a file size limit?▼

No imposed limit — but browser memory is finite. Practically: audio files up to ~30 minutes work fine on modern laptops; longer files may stutter or run out of memory. For long files, trim with our Audio Trimmer or split with the Audio Splitter first.

Can I add multiple images or animations?▼

Not in this tool — it's optimized for the single-still-image case (which is what 95% of YouTube audio uploads use). For animated visualizers, see our tool index; an Audio Waveform Video Generator is on the roadmap.