AAC to Opus Converter
Inspect any audio file in your browser to see its duration, size, and sample rate — then copy the ready-to-run FFmpeg command to convert it from AAC to Opus.
Audio File Inspector
Drop or select any audio file. It is decoded locally in your browser — no data is uploaded to any server.
| File name | — |
| File type | — |
| File size | — |
| Duration | — |
| Sample rate | — |
FFmpeg Command Generator
Also accepts .m4a, .mp4, or any AAC-containing file.
ffmpeg -i "input.aac" -c:a libopus -b:a 96k -vbr on "input.opus"
Install FFmpeg free at ffmpeg.org. Run this command in your terminal after replacing the file name.
Batch convert AAC files (Linux / macOS)
for f in *.aac; do ffmpeg -i "$f" -c:a libopus -b:a 96k -vbr on "${f%.aac}.opus"; done
Batch convert M4A files (Linux / macOS)
for f in *.m4a; do ffmpeg -i "$f" -c:a libopus -b:a 96k -vbr on "${f%.m4a}.opus"; done
Enter audio duration below, or inspect a file above to auto-fill.
hrs
min
sec
Formula: bitrate (kbps) × duration (s) / 8000
32 kbps
—
64 kbps
—
96 kbps
—
128 kbps
—
48 kbps
—
Duration: 3 min 30 sec (210 s)
Why No In-Browser Conversion?
Browsers expose the Web Audio API for decoding audio, but they do not include an Opus encoder. Opus encoding requires libopus — a native library compiled for your operating system. FFmpeg bundles libopus and handles the full pipeline:
- 1 FFmpeg opens the AAC or M4A container and reads the compressed audio stream.
- 2 The AAC decoder decompresses the stream to raw PCM audio in memory.
- 3 libopus re-encodes the PCM data to Opus at the bitrate you specify.
- 4 FFmpeg wraps the Opus stream in an OGG container and writes the .opus file to disk.
Install FFmpeg at ffmpeg.org (free, open-source). On Linux: sudo apt install ffmpeg. On macOS: brew install ffmpeg.
Opus Bitrate Reference
| Bitrate | Quality | Size / min | Best For |
|---|---|---|---|
| 24 kbps | Acceptable | ~0.18 MB | Voice calls, minimal bandwidth |
| 32 kbps | Good | ~0.24 MB | Podcasts, audiobooks, speech |
| 48 kbps | Very Good | ~0.36 MB | Speech, transparent for voice |
| 64 kbps | Excellent | ~0.48 MB | Casual music listening |
| 96 kbps | Near-transparent | ~0.72 MB | General music, headphones |
| 128 kbps | Transparent | ~0.96 MB | Audiophile, archival Opus |
AAC vs. Opus — At a Glance
AAC (Advanced Audio Coding)
- Default format for Apple Music, YouTube, mobile
- Very broad hardware and software support
- Used by all major streaming platforms
- Lower quality than Opus at equivalent low bitrates
- Larger file sizes for the same perceived quality
Opus (RFC 6716, libopus)
- Outperforms AAC at most bitrates, especially below 128 kbps
- Royalty-free and open-source (Xiph.org / IETF)
- Native support in all major browsers and WebRTC
- Not supported by older car stereos or dedicated audio players
- Apple devices have limited native Opus support outside browsers
Summary
Inspect any audio file in your browser to see its duration, size, and sample rate — then copy the ready-to-run FFmpeg command to convert it from AAC to Opus.
How it works
- Drop or select an audio file in the inspector panel — the file never leaves your device.
- The Web Audio API decodes the file header and reports duration, file size, and sample rate.
- Enter your file name and choose a target Opus bitrate in the command generator.
- Copy the generated FFmpeg command and paste it into your terminal.
- FFmpeg decodes the AAC stream, re-encodes it as Opus inside an OGG or WebM container, and writes the output file.
- Play the output file to verify quality, then delete the original AAC if no longer needed.
Use cases
- Convert Apple Music or iPhone voice memos from AAC to the more efficient Opus format.
- Reduce podcast episode file sizes significantly with Opus at 32–64 kbps versus AAC at 128 kbps.
- Prepare audio for WebRTC or web streaming where Opus is natively supported.
- Batch-convert an entire AAC library to Opus to save storage space.
- Inspect an unknown audio file to confirm its duration and sample rate before processing.
- Generate ready-to-paste FFmpeg commands without memorizing Opus encoder flags.
- Compare AAC and Opus quality characteristics before choosing a target bitrate.
- Convert audiobooks or lecture recordings from AAC to Opus for efficient long-term storage.