Convert AVI to AAC — Free Online Tool
Extract and convert the audio track from an AVI file to AAC format, discarding the video stream entirely and encoding the audio using the AAC codec at 128k bitrate by default. AAC delivers better sound quality than the MP3 audio commonly found in AVI files at equivalent bitrates, making this ideal for archiving or streaming audio from legacy video content.
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FFmpeg Command
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Estimated output:
Conversion Complete!
DownloadHow It Works
AVI files typically store audio using codecs like MP3 (libmp3lame) or occasionally AAC or Vorbis, interleaved with a video stream in Microsoft's legacy RIFF-based container. During this conversion, FFmpeg reads the AVI container, strips the video stream entirely, and re-encodes the audio track using the native AAC encoder. If the source AVI already contains AAC audio, re-encoding still occurs because the raw AAC stream must be extracted and repackaged — AVI's interleaved structure does not allow a clean stream copy to a bare .aac file without decoding and re-encoding. The output is a raw AAC audio stream with no container wrapper (or a minimal ADTS wrapper), containing only the audio at your chosen bitrate.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, which handles reading the AVI container, demuxing the interleaved audio and video streams, decoding the audio, re-encoding it to AAC, and writing the output file. |
-i input.avi
|
Specifies the input AVI file. FFmpeg reads the RIFF-based AVI container and identifies all available streams — in this case at minimum one video stream and one audio stream — before processing begins. |
-c:a aac
|
Instructs FFmpeg to encode the audio stream using its built-in native AAC encoder. This re-encodes whatever audio codec was used in the source AVI (most commonly MP3) into AAC, which offers better compression efficiency and is natively supported by Apple devices, browsers, and most modern streaming platforms. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second. At this rate, AAC produces audio quality that is generally considered transparent for speech and acceptable for music — and noticeably cleaner than MP3 at the same bitrate, which is the most common audio format found in AVI source files. |
output.aac
|
Defines the output file as a raw AAC audio stream with ADTS framing. The .aac extension signals FFmpeg to write only the audio — the video stream from the AVI is automatically discarded because the AAC format cannot contain video data. |
Common Use Cases
- Extract a speech recording or interview captured in an old AVI format to AAC for uploading to a podcast platform or streaming service that requires audio-only files.
- Pull the audio soundtrack from a legacy AVI home video to store as a smaller AAC file for playback on an iPhone or iPad, which natively supports AAC but may struggle with older AVI variants.
- Convert AVI audio to AAC for use in a video editing project where the NLE requires audio-only assets in a modern, widely compatible format.
- Archive the audio commentary or narration track from an AVI screencast or tutorial video as a standalone AAC file for distribution without the video.
- Reduce storage footprint by extracting only the audio from large AVI files where the video content is no longer needed, using AAC's efficient compression to keep file sizes small.
- Prepare audio from AVI footage for use in an Apple ecosystem workflow — iTunes, GarageBand, or Final Cut Pro — where AAC is the preferred and natively supported audio format.
Frequently Asked Questions
Yes, this is a lossy conversion regardless of what audio codec the source AVI uses. If the AVI contains MP3 audio (the most common case), you are transcoding from one lossy format to another, which introduces a second generation of compression artifacts. At the default 128k bitrate, AAC generally sounds better than MP3 at the same rate, but if audio fidelity is critical, you should raise the bitrate to 192k or 256k to minimize the impact of this generation loss.
When the output format is a bare .aac file, FFmpeg automatically understands that no video stream can be written to that container and silently discards it. The AAC format specification does not support video, so FFmpeg infers -vn implicitly. If you were outputting to a container like MP4 or MKV instead, you would need to explicitly add -vn to drop the video stream.
Replace the value after -b:a with your desired bitrate. For example, use -b:a 192k for higher quality or -b:a 96k for a smaller file. For speech-only content from AVI recordings, 96k AAC is usually indistinguishable from higher rates. For music or high-fidelity audio originally captured in the AVI, 192k or 256k is recommended to avoid audible artifacts introduced by the transcoding step.
Yes, with a small shell script. On Linux or macOS, run: for f in *.avi; do ffmpeg -i "$f" -c:a aac -b:a 128k "${f%.avi}.aac"; done. On Windows Command Prompt, use: for %f in (*.avi) do ffmpeg -i "%f" -c:a aac -b:a 128k "%~nf.aac". Each AVI file in the directory will be processed in sequence, producing a matching .aac file.
AVI has very limited metadata support compared to modern formats, and bare AAC files (.aac with ADTS framing) have essentially no standardized metadata container. Any ID3-style tags embedded in the AVI's audio stream are unlikely to survive this conversion. If preserving metadata is important, consider outputting to .m4a (an AAC stream in an MP4 container) instead, which fully supports iTunes-compatible metadata tags.
By default, FFmpeg selects the first audio stream in the AVI file. AVI does support multiple audio tracks, though this is uncommon. If your file has multiple audio streams and you want a specific one, add -map 0:a:1 (for the second audio track) to the command before the output filename: ffmpeg -i input.avi -map 0:a:1 -c:a aac -b:a 128k output.aac. Use ffmpeg -i input.avi with no output to inspect how many audio streams the file contains.
Technical Notes
AVI (Audio Video Interleave) stores audio and video in interleaved RIFF chunks, and the most common audio codec found in AVI files is MP3 (encoded via libmp3lame), though PCM, AC3, and occasionally AAC are also encountered. Converting to a bare .aac file produces an ADTS-framed AAC stream, which is widely playable but lacks a proper container for chapters, metadata, or cover art. FFmpeg's built-in AAC encoder (used here as -c:a aac) is a solid native implementation suitable for most use cases; if you have FFmpeg compiled with libfdk_aac, substituting -c:a libfdk_aac generally yields slightly better quality at the same bitrate and is considered the gold standard for AAC encoding. One important limitation: AVI does not support subtitle streams or chapter markers, so no data of that kind will be present in the source to lose. The output .aac file will also not preserve any AVI-level metadata such as the creation date or encoder string. For Apple device compatibility, the output AAC is fully supported on iOS and macOS natively. File size relative to the source AVI will be dramatically smaller since the entire video stream is discarded and only the audio remains.