Opus
The most efficient audio codec, mandatory for WebRTC.
Overview
What It Is
Advanced Audio Coding (AAC) is a lossy audio compression standard developed by the MPEG consortium as the successor to MP3. Standardized in 1997 (ISO/IEC 13818-7) and updated through multiple profiles (LC, HE-AAC, HE-AACv2, xHE-AAC), AAC delivers better audio quality than MP3 at equivalent bitrates. AAC is the mandatory audio codec for HLS streaming and the default audio format across Apple’s ecosystem (iTunes, Apple Music, iOS). AAC-LC at 128 kbps is the most common audio configuration for streaming video, offering excellent quality for music and dialogue.
Decision Guide
When to Choose AAC
Choose AAC when:
- You are delivering audio inside HLS streams — AAC is required by Apple’s HLS specification and supported by every HLS player.
- You need universal browser and device support — AAC plays in every browser, on every mobile OS, and on every smart TV.
- Your workflow involves the Apple ecosystem — AAC is the native audio format for iOS, macOS, and Apple devices.
Consider alternatives when:
- You are building a WebRTC application — Opus is mandatory for WebRTC and delivers better quality at low bitrates.
- You need the most bandwidth-efficient audio codec — Opus achieves transparent quality at 128 kbps vs. AAC’s 192 kbps.
- You need a completely royalty-free audio codec — Opus and Vorbis are royalty-free; AAC is licensed.
Reference
Key Characteristics
| Standard | ISO/IEC 13818-7 (MPEG-2) / ISO/IEC 14496-3 (MPEG-4) |
| Bitrate range | 8 kbps – 529 kbps |
| Sweet spot bitrate | 128 kbps (AAC-LC — high quality for most content) |
| Channels | Up to 48 channels (typically stereo or 5.1) |
| Latency | ~20ms (algorithmic delay, AAC-LC) |
| Sample rates | 8, 11.025, 12, 16, 22.05, 24, 32, 44.1, 48, 64, 88.2, 96 kHz |
| Royalty status | Licensed (Via Licensing patent pool) |
| Container support | MP4, HLS, DASH |
| Browser support | All browsers — Chrome, Firefox, Safari, Edge |
| Typical use case | HLS audio, VOD streaming, Apple ecosystem, broadcast |
Compatibility
Browser & Device Support
Platform | AAC | MP3 | Opus | Vorbis |
|---|---|---|---|---|
Chrome (desktop) | 33+ | |||
Firefox (desktop) | 15+ | |||
Safari (macOS) | 14.1+ | |||
Edge | 79+ | |||
iOS Safari | 14.5+ | |||
Android Chrome |
Implementation
How Qencode Handles AAC
AAC is the default audio codec for HLS and MP4 output in Qencode. Unless you specify a different audio codec, Qencode automatically uses AAC-LC. Configure bitrate, sample rate, and channel layout through API parameters.
Pair AAC audio with Audio Normalization to standardize loudness levels across your library before encoding.
Request Example
AAC audio in MP4 output
{
"query": {
"source": "https://your-storage.com/video.mp4",
"format": [
{
"output": "mp4",
"video_codec": "libx264",
"resolution": 2160,
"optimize_bitrate": 1,
"audio_codec": "aac"
}
]
}
}Copy this payload and use it with your API key to encode AAC audio from any source.
Learn how to configure audio codec settingsComparison
AAC vs. Opus
AAC | Opus | |
|---|---|---|
Transparent quality | 192 kbps | 128 kbps |
Royalty status | Licensed | Royalty-free |
HLS support | Required (default) | Not standard in HLS |
WebRTC support | Not standard | Required (mandatory) |
Latency | ~20ms | 2.5–60ms (configurable) |
Best for | HLS streaming, Apple ecosystem | WebRTC, low-bitrate, low-latency |
For a detailed Opus breakdown, see Opus
Explore More
Related Technologies
HLS
The adaptive streaming format that requires AAC audio.
Audio Normalization
Standardize audio levels across your library.
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