Convert MP4 to AAC — Free Online Converter

MP4 to AAC conversion extracts the audio track from an MPEG-4 video and saves it as a standalone Advanced Audio Coding file. AAC is the audio codec used by Apple Music, YouTube, and most streaming services — it delivers better sound quality than MP3 at equivalent bitrates. Since MP4 containers almost always carry AAC audio internally, this conversion is often a simple demux operation that copies the existing audio stream without re-encoding.

Our converter detects the audio codec inside your MP4 file. When it finds AAC audio, it performs a direct stream copy in milliseconds with zero quality loss. When the source contains a different codec (AC3, DTS, PCM), it transcodes to AAC using the high-quality native FFmpeg encoder.

You want the sound from a video without the video. Extracting audio as AAC gives you a high-quality audio file at roughly one-tenth the size of the original MP4. Podcasters pull interview audio from video recordings. Musicians isolate backing tracks from concert footage. Language learners extract dialogue for listening practice. AAC is preferred over MP3 because it preserves higher frequencies at the same bitrate — 128 kbps AAC sounds comparable to 192 kbps MP3.

FFmpeg reads the MP4 container and inspects the audio stream codec. If the stream is already AAC (codec_name: aac), the converter uses -c:a copy to extract the raw AAC stream without decoding or re-encoding. The output is wrapped in an ADTS container with the .aac extension. If the source audio is not AAC, FFmpeg decodes it and re-encodes using the native AAC encoder at 256 kbps stereo by default, with VBR mode available for variable bitrate output.