AMR vs Opus: Speech Codec Comparison

Compare AMR and Opus speech codecs for mobile and VoIP.

Legacy vs Modern Standard

AMR (Adaptive Multi-Rate) was developed in 1999 as the 3GPP standard for mobile speech communication. It became ubiquitous in 3G cellular networks and remains the standard for voice calls in mobile devices. Opus was designed in 2012 as the modern successor to various speech codecs, standardized by IETF for real-time communication. Opus replaced AMR in modern applications but AMR persists in cellular infrastructure. Understanding this distinction: AMR is legacy standard still widely supported.

Opus is modern standard for new applications.

Compression Efficiency

Both codecs are designed for speech compression at very low bitrates: AMR supports bitrates from 4.75 to 12.2 kbps for speech. Opus supports 6 to 128 kbps (adapts to content). At equivalent bitrates (8-12 kbps): AMR delivers acceptable voice quality, noticeable compression artifacts for critical listeners. Opus delivers noticeably better voice quality with fewer artifacts. Opus efficiency advantage is particularly pronounced at low bitrates.

Real-time Communication

Both codecs are designed for real-time voice communication with low latency. AMR latency: 20-100ms (variable frame-based). Opus latency: 5-65ms (configurable, lower than AMR). For interactive voice calls, both provide acceptable experience. Opus lower latency makes it slightly preferable for highly interactive applications.

Device Support and Adoption

AMR support is ubiquitous in older mobile devices due to cellular standard compliance. Almost all phones support AMR voice calls. Opus support: all modern smartphones support Opus natively or via apps. Most computers support Opus. Older devices may lack Opus native support. For cellular voice calls, AMR remains standard. For VoIP applications, Opus dominates.

Use Case Specialization

AMR is optimized specifically for speech, particularly at very low bitrates required by cellular networks. Opus is flexible, handling both speech and music efficiently. AMR is the cellular standard; Opus is the Internet standard. Choose AMR for legacy mobile compatibility. Choose Opus for modern applications.

Encoding Complexity

AMR encoding is computationally simple, designed for implementation on low-power mobile processors from the 1990s. Opus encoding is more complex, requiring more powerful processors, but still efficient on modern phones. Both decode efficiently with minimal battery drain.

Future Outlook

AMR will persist as long as cellular infrastructure exists, but is being gradually superseded by Opus and newer codecs in VoIP and data applications. Opus is the modern standard for real-time communication. For new applications, Opus is the appropriate choice. AMR is maintained for backward compatibility with cellular systems.

Patent and Licensing Status

Both AMR and Opus have complex patent histories. AMR patents are held by various organizations; licensing can be complicated. Opus is designed as patent-free, IETF-standard codec to avoid licensing complications. For new applications, Opus patent-free nature is advantageous.

Quality at Mobile Bitrates

At mobile bitrates (8-12 kbps): AMR delivers functional voice communication, intelligible speech, acceptable quality for phone calls. Opus delivers noticeably better quality, more natural-sounding speech, fewer artifacts. Both are acceptable for cellular voice calls; Opus is preferred for quality-conscious applications.