Convert MP4 to AAC
Extract the AAC audio elementary stream from MP4 video files directly in your browser. Because MP4 already carries AAC as its standard audio codec, we stream-copy it out — the .aac file is bit-identical to the audio inside the MP4. Instant, lossless, no upload.
Drag 'n' drop files here, or
click to select files
.mp4
Drop your files and click Convert to get AAC
//when_to_use
When to Convert MP4 to AAC
- Pulling AAC audio out of MP4 podcast episodes without any re-encode for direct distribution
- Extracting AAC tracks from MP4 lecture recordings for upload to AAC-only podcast hosts and audio-feed RSS
- Stripping AAC audio from MP4 music videos as a quick low-bandwidth listening copy without quality loss
- Pulling AAC tracks from MP4 conference recordings to feed into AAC-native transcription pipelines
- Extracting AAC audio from screencasts for bundling alongside video as lightweight audio-only versions
//comparison
MP4 vs AAC
| Property | MP4 | AAC |
|---|---|---|
| Type | Video container | Raw audio elementary stream |
| Process | — | Stream copy (no re-encode) |
| Quality loss | — | Zero (bit-identical) |
| Speed | — | Near disk read speed |
| File size | Includes video | Audio only (~5-15% of MP4) |
| Best for | Watching, streaming | Audio-only podcast, ADTS pipelines |
//how_it_works
How It Works
Drop your MP4 files
Drag and drop or pick .mp4 files. First conversion loads FFmpeg WASM (~30MB).
FFmpeg demuxes the audio track
FFmpeg WASM parses ISOBMFF boxes, isolates the AAC audio track, and discards the video track.
Stream copy to ADTS .aac
Audio samples are written verbatim into ADTS frames (-c:a copy -f adts). No decoding, no re-encoding — bit-identical output.
Download .aac files
Raw AAC streams play in VLC, foobar2000, Winamp, every browser via HTML5 <audio>, and any AAC-capable hardware player.
// under the hood
MP4 is an ISOBMFF container carrying AAC audio inside its sample tables. .aac is the raw AAC ADTS (Audio Data Transport Stream) format. Our converter uses FFmpeg WASM with -c:a copy and -bsf:a aac_adtstoasc reversed (-vn -acodec copy -f adts) to remux the AAC elementary stream — bit-identical samples, no decode, no encode.
//faq
Frequently Asked Questions
- Is this lossless? I thought AAC was lossy.
- The extraction itself is lossless even though AAC is a lossy codec. We stream-copy the AAC elementary stream out of the MP4 container as-is into an ADTS .aac file — no decoding, no re-encoding, bit-identical samples. You keep exactly the audio quality the MP4 already had.
- Why pick AAC over MP3 when extracting?
- If your MP4's audio is AAC (it almost always is), extracting to AAC is instant and quality-preserving. Going to MP3 requires a full re-encode (AAC → PCM → MP3), which adds processing time and lossy generational loss. AAC also sounds better than MP3 at every bitrate.
- What if the MP4 doesn't contain AAC?
- Rare, but possible (older MP4s sometimes hold MP3 or AC-3). In that case we fall back to a re-encode to AAC-LC at 192 kbps. The notification banner will say so.
- What's the difference between .m4a and .aac?
- .m4a is AAC wrapped in an MP4/ISOBMFF container (with proper random-access, tags, album art). .aac is the raw ADTS elementary stream — smaller, simpler, but with no chapter/seek metadata. Most players accept both; if your tool only takes one, try .m4a first.
- Are my MP4 files uploaded?
- No. FFmpeg WebAssembly performs the demux + stream copy in your browser tab — no server contact at all.
//related_converters
Related Converters
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Convert MP4 to MP3
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→Convert MP4 to WebM
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→Convert MP4 to MOV
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→Convert MP4 to AVI
Convert MP4 videos to AVI format for legacy software and devices.
→Convert MP4 to WAV
Extract uncompressed WAV (PCM) audio from MP4 video for editing in DAWs and audio analysis tools.
→Convert MP4 to OGG
Extract Ogg Vorbis audio from MP4 video for use in games, royalty-free pipelines, and HTML5 <audio>.
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