Convert MP4 to AAC Online
Extract AAC audio from any MP4 video. Free, in your browser, no file uploads.
.mp4 · up to 100 MB
What you can do
Extract AAC audio from MP4 in seconds
iPhone ringtone pipeline
Extract the AAC, rename it to .m4r and you have your custom ringtone ready to import.
100% private
Your video never leaves your device. FFmpeg.wasm processes everything in local WebAssembly.
Stream copy when possible
If the MP4 already has AAC audio, extraction is instant and without additional quality loss.
Podcast distribution
Get the AAC ready for Anchor, Buzzsprout, Apple Podcasts, or any distribution platform.
How it works
Three steps, no hassle
Upload your MP4 file
Drag or select your .mp4 video — iPhone recording, downloaded video, screen capture, or podcast clip. Up to 500 MB, no signup.
AAC audio extraction
FFmpeg.wasm identifies the audio track inside the MP4 container. If it's already AAC, it performs a direct stream copy without re-encoding — maximum speed and zero additional quality loss.
Download your AAC file
Get the audio ready for iTunes, Apple Music, podcast distribution, or rename it to .m4r to use as an iPhone ringtone.
FAQ
Got questions?
Stream copy is an operation where FFmpeg extracts the audio track from the MP4 container and places it into an AAC/M4A container without re-encoding it. This is possible when audio is already in AAC format inside the MP4 — which is the case with virtually all videos recorded with iPhone, iPad, GoPro, Sony or Canon DSLRs, and YouTube videos downloaded at 1080p or 4K. Without re-encoding, conversion is instant (a 1 GB video can be processed in seconds) and the resulting audio is bit-for-bit identical to the original.
Yes. iPhone ringtones are AAC files in an MPEG-4 container with an .m4r extension (instead of .m4a or .aac). The process: convert your MP4 to AAC here, download the file, rename it changing the extension to .m4r, and drag it to the ringtones library in iTunes or Finder (macOS Ventura and later). The ringtone must be under 40 seconds to be accepted by iOS.
Both are AAC-encoded audio, but in different containers. The .aac file uses ADTS (Audio Data Transport Stream), a simple container designed for streaming. The .m4a file uses the MPEG-4 Part 14 container (same as .mp4 but without a video track), which allows rich ID3 metadata: album art, composer, genre, lyrics, year. For Apple Music, podcasts, and modern players, .m4a is preferable.
Yes. Apple Music, Spotify, Amazon Music HD, and the major podcast distribution platforms (Anchor/Spotify for Podcasters, Buzzsprout, Podbean, Transistor) accept AAC/M4A as a delivery format. Apple Music specifically recommends AAC at 256 kbps (AAC-LC) for submissions to their catalog via iTunes Connect. For podcasts, the industry standard is AAC-LC at 128 kbps mono or 192 kbps stereo.
Some MP4 videos contain audio in MP3, Opus, AC-3 (Dolby Digital), or PCM/LPCM. In those cases direct stream copy to AAC is not possible and FFmpeg performs a transcode: it decodes the audio from the original format and re-encodes it to AAC-LC. The resulting quality depends on the target bitrate — Convertir.ai uses 192 kbps by default, which is transparent for most content.
The current version of Convertir.ai converts the complete file. To extract a specific segment, the most efficient tool is FFmpeg from the command line: ffmpeg -i video.mp4 -ss 00:00:00 -t 00:03:00 -vn -acodec copy segment.aac — this extracts exactly the first 3 minutes with stream copy. Alternatively, extract the full AAC here and trim it with Audacity or any audio editor.
Convert MP4 to AAC: extract AAC audio from video with maximum quality
Converting MP4 to AAC is a technically efficient operation because the MP4 container (MPEG-4 Part 14, specified in ISO/IEC 14496-14) and the AAC format share the same MPEG-4 standards family. In practice, this means virtually every MP4 video recorded with modern devices — iPhone from the first model, iPad, GoPro Hero (all generations), Sony Alpha cameras, Canon EOS R, Fujifilm X-Series, Samsung Galaxy — already contains audio encoded in AAC-LC (Advanced Audio Coding Low Complexity), standardized in ISO/IEC 13818-7 in 1997. When audio is already AAC inside the MP4, conversion requires no re-encoding: FFmpeg simply extracts the audio track from the ISOBMFF container and places it in a new AAC or M4A container via stream copy, an operation that processes at disk-read speeds (typically 100–500 MB/s) with minimal CPU load.
The most frequent use cases for extracting AAC from MP4 cover three main areas. First, podcast distribution: content creators who record in video (Zoom, Riverside.fm, Squadcast, direct iPhone recording) need to extract audio in a format compatible with distributors. AAC at 128 kbps mono meets the technical requirements of Apple Podcasts, Spotify for Podcasters, Amazon Music, and Pocket Casts. Second, the iPhone ringtone (M4R) workflow: .m4r files that iOS accepts as custom ringtones are exactly AAC files in an MPEG-4 container with a renamed extension, so extracting AAC from an MP4 video is the first step of any ringtone creation pipeline. Third, Apple Music uploads as an independent distributor: DistroKid, TuneCore, CD Baby, and Amuse accept M4A/AAC as an alternative delivery format to WAV for independent artists.
Convertir.ai runs AAC extraction from MP4 entirely in the browser via FFmpeg.wasm. The technical process begins by analyzing the ISOBMFF container to identify metadata atoms (moov, trak, hdlr, stsd) that describe the audio and video streams present in the file. If the audio codec identified in the stsd atom is mp4a (the ISOBMFF designation for AAC in its LC, HE-AACv1, and HE-AACv2 variants), FFmpeg proceeds with stream copy by extracting audio samples from mdat atoms and rewriting them into the destination container. If the codec is different (opus, mp3, ac-3) a transcoding pipeline runs using FFmpeg's native aac encoder or libfdk_aac if available in the build, with a target bitrate of 192 kbps by default. The resulting file can be downloaded as .aac (ADTS) or .m4a (MPEG-4 container with full metadata).