Add your MP4 file
Drop one or more .mp4 files onto the converter above, or browse for them. They load into browser memory only. Nothing is uploaded, so there is no size-based pricing and no server queue.
MP4 to AAC
Pulling the soundtrack out of a .mp4 video into .aac audio keeps what you can hear and drops the picture entirely. Free, private, and validated: the file never leaves your browser.
Private for supported formats, processed in your browser
Runs on your deviceConvert supported files
Drop MP4 files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting MP4 video to AAC audio
Pulling the soundtrack out of a .mp4 video into .aac audio keeps what you can hear and drops the picture entirely. An .mp4 file is a multimedia container that bundles compressed video, audio, subtitles, and chapter data into a single stream-friendly package. It is the default delivery format for nearly every phone, camera, and video platform, which makes .mp4 the safest target when a clip has to play everywhere.
An .aac file holds raw Advanced Audio Coding data, usually as an ADTS stream. AAC was designed as MP3's successor and delivers audibly better quality at the same bitrate, though the bare .aac extension is rarer than AAC audio traveling inside .m4a or .mp4 files. For this route the practical draw is noticeably more efficient than MP3 at equal bitrates and hardware decoding in essentially every phone and TV, balanced against raw ADTS files handle tags and cover art poorly, which is worth knowing before you commit a large batch.
Why convert MP4 to AAC?
The usual reason to take .aac audio out of a .mp4 file is that only the sound matters: a talk, interview, song, or podcast segment. Keeping the video stream would waste storage, and a dedicated audio file is easier to trim, tag, and play. On the source side, fewer track, attachment, and chapter features than Matroska; on the target side, the payoff is noticeably more efficient than MP3 at equal bitrates, which is exactly what you want for receiving the audio track copied out of MP4 video without re-encoding.
MP4 vs AAC at a glance
| Aspect | MP4 video (.mp4) | AAC audio (.aac) |
|---|---|---|
| Format type | Container: quality depends on the codecs and settings inside | Lossy: discards detail it judges invisible to shrink files |
| How it stores data | typically carries H.264/AVC or H.265/HEVC video with AAC audio, though the box structure also accepts AV1, MP3, and timed-text tracks | a pure MDCT transform codec, free of the hybrid filterbank compromise that limited MP3 |
| Strongest at | publishing video to the web, social media, or a client who has not specified a format | receiving the audio track copied out of MP4 video without re-encoding |
| Weak spot | fewer track, attachment, and chapter features than Matroska | raw ADTS files handle tags and cover art poorly |
| Metadata | iTunes-style metadata atoms (title, artist, cover art) plus XMP and per-track language tags; ID3 is not native to the container. A conversion here writes none of it. Every media command this app runs disables metadata mapping, so title, artist, cover art, XMP and per-track language tags are dropped, and because only the default video and audio streams are selected, chapters, subtitle tracks, timecode tracks and any additional audio languages go with them | no standard tag container exists for raw ADTS streams; ID3 tags are sometimes prepended but poorly supported, so wrapping in .m4a is the reliable way to tag AAC. Wrapping it here will not help: metadata mapping is disabled on every route, so the .m4a this app writes is as untagged as the .aac, and tagging has to happen afterwards in a player or tag editor |
Pick AAC as the output
Select .aac in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if AAC is selectable, the route is real and validated.
Convert on your device
Press Convert. A WebAssembly FFmpeg build demuxes the audio track and re-encodes it locally; the video stream is simply discarded.
Verify and download
Each result is checked before the download unlocks: where AAC has a signature or a structure this converter can read back, the file is re-opened and parsed, and where it has neither, the check is that a non-empty file of the declared type came back. A result that fails is reported as an error instead of being offered for download, and outputs keep the original filename with the .aac extension.
MP4 to AAC questions, answered
Will converting MP4 to AAC lose quality?
Since mp4 is container-oriented and aac is lossy-oriented, the conversion preserves the source content exactly as stored; no additional compression pass is applied beyond what .aac itself requires.
Is it private to convert MP4 files here?
Yes. The .mp4 file is processed inside your browser tab and never uploaded. A WebAssembly FFmpeg build demuxes the audio track and re-encodes it locally; the video stream is simply discarded. Close the tab and the file is gone from memory.
Where will the AAC file work?
AAC decoding is built into every browser, phone, and operating system, whether the audio arrives as a raw .aac stream or inside an .m4a wrapper. The last holdouts are elderly MP3-only car stereos and bargain portable players. Novus Convert reads .aac and writes it as a raw ADTS elementary stream, using FFmpeg's built-in AAC encoder at a constant bitrate the quality slider sets between 55 and 192 kbps. That is a narrow band by AAC standards, so the top of the slider is 192 kbps and no higher, and there is no variable-bitrate or HE-AAC mode on this route. Choose the .m4a target instead if you want the same audio in an MPEG-4 wrapper. Input is capped at 500 MB.
Will the AAC file be bigger or smaller than my MP4?
Much smaller: the video stream is usually 80–95% of a .mp4 file's weight, and it is discarded entirely. The remaining audio is re-encoded at the bitrate implied by your quality setting.
What happens to the metadata in my MP4 file?
This converter strips container metadata deliberately (the FFmpeg command runs with metadata mapping disabled) so exported files do not leak recording details. In the source, iTunes-style metadata atoms (title, artist, cover art) plus XMP and per-track language tags; ID3 is not native to the container. A conversion here writes none of it. Every media command this app runs disables metadata mapping, so title, artist, cover art, XMP and per-track language tags are dropped, and because only the default video and audio streams are selected, chapters, subtitle tracks, timecode tracks and any additional audio languages go with them; none of it is transmitted anywhere because the file never leaves your browser.