How to convert a video soundtrack to aac with no re-encode
- Step 1Confirm the source audio is AAC — Stream-copy to AAC only works when the source audio is AAC (the default for MP4/MOV/M4V from cameras, phones, and most editors). WebM/MKV with Opus or Vorbis audio can't be AAC-copied — for those, use a re-encode format.
- Step 2Open the extractor — Load audio-track-extractor. FFmpeg.wasm runs locally; the file is never uploaded.
- Step 3Drop the video — Add one MP4, MOV, M4V, MKV, or other AAC-bearing file. Free tier accepts up to 1 GB; Pro 10 GB; Pro + Media 100 GB.
- Step 4Choose AAC in the Format dropdown — Set Format to AAC. This selects the
-c:a copypath — the only stream-copy option in the tool. No bitrate or quality control is needed because nothing is re-encoded. - Step 5Run the copy — The engine runs
-i input -vn -c:a copy out.aac. With no encode pass it completes quickly. If the source audio isn't AAC, the copy fails — switch to MP3/WAV/FLAC/Opus to re-encode instead. - Step 6Save the bit-identical AAC — On Chromium it can stream to a chosen folder; otherwise it downloads as
<name>.aac. The bytes match the source audio exactly — verify by comparing duration and bitrate against the original.
Stream-copy vs re-encode across the five formats
AAC is the only stream-copy path. Every other format decodes and re-encodes (losslessly for WAV/FLAC, lossily for MP3/Opus).
| Format | FFmpeg args | Touches the signal? | Speed |
|---|---|---|---|
| AAC | -c:a copy | No — bit-identical | Fastest (no encode) |
| WAV | -c:a pcm_s16le | Re-encode (lossless) | Moderate |
| FLAC | -c:a flac | Re-encode (lossless) | Slower (compress) |
| MP3 | -c:a libmp3lame -b:a 192k | Re-encode (lossy 192k) | Moderate |
| Opus | -c:a libopus -b:a 128k | Re-encode (lossy 128k) | Moderate |
Will the AAC stream-copy succeed?
Whether AAC copy works depends entirely on the source audio codec, since you can only copy AAC packets into an AAC file.
| Source container | Likely audio codec | AAC copy result |
|---|---|---|
| MP4 (phone/camera) | AAC | Succeeds — bit-identical copy |
| MOV (editor export) | AAC | Succeeds — bit-identical copy |
| M4V | AAC | Succeeds — bit-identical copy |
| MKV (varies) | AAC, AC-3, Opus, or others | Succeeds only if audio is AAC |
| WebM | Opus or Vorbis | Fails — use a re-encode format |
Cookbook
Real AAC stream-copy jobs and the cases where copy is the wrong choice. AAC copy is the no-loss path when (and only when) the source is AAC.
Phone MP4 to bit-identical AAC
A phone MP4 stores AAC audio. AAC copy demuxes it untouched — same bitrate, same bytes, near-instant.
Source: clip.mp4 (AAC 256 kbps) Format: AAC Command: ffmpeg -i clip.mp4 -vn -c:a copy clip.aac Result: clip.aac (AAC 256 kbps — identical to source audio) No encode pass: completes in seconds even for long clips.
Editor MOV export, audio extracted for re-mux
You exported a MOV from an NLE and want the original AAC to re-mux into a different container without re-encoding it.
Source: master.mov (AAC) Format: AAC Result: master.aac (untouched AAC stream) Drop master.aac into your target container; quality intact.
WebM with Opus — AAC copy fails
A downloaded WebM almost always carries Opus audio. You cannot copy Opus packets into an AAC file, so the copy fails. Pick a re-encode format instead.
Source: download.webm (Opus audio)
Format: AAC
Result: FAILS — can't stream-copy Opus into .aac
Fix: choose MP3/WAV/FLAC (re-encode) or Opus (copy-friendly
re-encode). For Opus output see the Discord guide.MKV with AC-3 audio — AAC copy not valid
A broadcast-style MKV may carry AC-3 (Dolby Digital). AC-3 can't be copied into an AAC stream, so AAC fails here too — re-encode to keep the audio.
Source: recording.mkv (AC-3 audio) Format: AAC Result: FAILS — AC-3 packets are not AAC Fix: WAV/FLAC for lossless re-encode, or MP3 for portable.
Confirming a copy was truly lossless
After an AAC copy, the output bitrate and duration should match the source audio exactly — that's the signature of a stream-copy versus a re-encode.
Source audio: AAC, 256 kbps, 04:31.2 Output .aac: AAC, 256 kbps, 04:31.2 <- identical A re-encode would have changed the bitrate (e.g. 192k MP3) and re-derived the stream. Copy keeps both unchanged.
Edge cases and what actually happens
Source audio is not AAC
FailsAAC stream-copy only works when the source packets are AAC. A WebM/MKV with Opus, Vorbis, AC-3, or another codec cannot be copied into an .aac file, so FFmpeg exits with an error. Switch the Format dropdown to MP3/WAV/FLAC/Opus to re-encode instead.
Container/extension mismatch on copy
FailsEven when the codec is AAC, certain container quirks (unusual ADTS/ASC headers, fragmented MP4) can make a raw .aac rewrap fail. The tool surfaces the FFmpeg error rather than producing a broken file. If copy fails on an AAC source, re-encode to WAV/FLAC for a guaranteed clean output.
AAC copy is bit-identical, not 'better'
By designStream-copy preserves the source AAC exactly — it does not upgrade quality. If the source AAC was 96 kbps, the copy is 96 kbps. Copy is about fidelity preservation and speed, not enhancement; there's no way to improve a lossy source by copying it.
Only the default audio track is copied
By designThere is no track-picker. The default (first) audio stream is the one copied. For a multi-track MKV with several AAC dubs, only the primary track is extracted in the current build.
Source has no audio
FailsIf the video has no audio stream, there are no packets to copy and FFmpeg errors out after -vn removes the video. Confirm the source actually contains an AAC audio track.
Original AAC delay/offset is preserved
PreservedA stream-copy keeps the source's original timing, including any encoder delay or container offset baked into the AAC track. Re-importing the copied AAC into an editor preserves that timing exactly — usually what you want for a faithful copy.
Want lossless but source isn't AAC
Use FLAC insteadIf you need a no-loss extract but the source audio is Opus/Vorbis/PCM rather than AAC, AAC copy won't apply. Use FLAC (-c:a flac) — it re-encodes losslessly, preserving the full decoded signal even though it isn't a byte-copy.
Copy is dramatically faster than re-encode
ExpectedBecause no encoder runs, AAC copy finishes far quicker than MP3/WAV/FLAC/Opus on the same source — it's essentially limited by read/write speed. That speed is a useful tell that the copy actually happened rather than silently re-encoding.
Frequently asked questions
What does 'no re-encode' actually mean here?
AAC output uses -c:a copy, which demuxes the AAC audio packets out of the container and rewraps them into an .aac file without ever decoding or re-encoding. The output is bit-identical to the audio inside the source — true stream-copy, the only such path in this tool.
Will AAC copy always work?
Only when the source audio is AAC. Most MP4/MOV/M4V files from cameras, phones, and editors are AAC, so it usually works. WebM (Opus), some MKV files (AC-3, Vorbis), and other non-AAC sources will fail the copy — choose a re-encode format for those.
Why did my AAC extract fail?
Almost always because the source audio isn't AAC. You can't copy Opus, Vorbis, AC-3, or PCM packets into an .aac file. The fix is to pick MP3/WAV/FLAC/Opus, which re-encode and therefore work regardless of the source codec.
Is AAC copy lossless?
It's bit-identical to the source AAC — no quality is lost in the extraction. But the source AAC itself is a lossy format, so 'lossless' here means 'identical to what's already in the file,' not 'studio-master quality.' For a lossless container around the signal, use WAV or FLAC.
How is this different from extracting MP3?
MP3 always re-encodes the audio to 192 kbps (a new lossy generation). AAC copy doesn't re-encode at all — it preserves the exact source audio. If your source is AAC and you want fidelity, AAC copy beats MP3; if you need a universally playable file, MP3 is more portable.
Why is the AAC extract so fast?
There's no encode pass. Stream-copy just demuxes and rewraps packets, so the operation is limited by how fast the file is read and written — far quicker than the re-encode formats. That speed is also a good sign the copy genuinely happened.
What file extension do I get?
An .aac file named after the source. It contains the original AAC audio stream untouched. You can re-mux it into another container (e.g. back into an MP4) without re-encoding.
Can I pick a specific AAC track from a multi-track file?
No — the tool copies the default (first) audio stream. There's no per-track selection control. For a multi-dub MKV, only the primary AAC track is extracted in the current build.
Does AAC copy upload my video?
No. The extraction runs in your browser via FFmpeg.wasm. Your file is processed locally and never sent to a server, so it's safe for confidential or unreleased material.
My source is Opus — what's the no-loss option?
AAC copy won't apply to an Opus source. For lossless, use FLAC (re-encodes losslessly, preserving the full decoded signal). If you specifically want Opus output, see the Opus guide — note that path re-encodes to 128 kbps.
Can I change the AAC bitrate during copy?
No — stream-copy by definition preserves the source bitrate exactly, and there's no bitrate control on the page anyway. If you need a different bitrate you'd have to re-encode (which AAC copy deliberately avoids); the tool doesn't offer an AAC re-encode at a custom bitrate.
What if I need to compress the whole video, not just copy audio?
This tool is audio-only. To shrink a video while keeping the picture, use a compressor such as discord-compressor or transcode with video-transcoder. AAC copy is purely for pulling the original audio out intact.
Privacy first
Every JAD Video tool runs entirely in your browser via WebCodecs and FFmpeg (WebAssembly). Your video files never leave your device — verified by zero outbound network requests during processing.