What is Opus Audio Codec: Applications and Significance [November 2023]

What is Opus?

Opus is a totally open, royalty-free, highly versatile audio codec. Opus is unmatched for interactive speech and music transmission over the Internet but is also intended for storage and streaming applications. It is standardized by the Internet Engineering Task Force (IETF).

A Brief History of Opus

In the rapidly evolving world of audio codecs, Opus has emerged as a significant player. The story of Opus begins with the realization that existing audio codecs, while effective in certain contexts, had limitations that hindered their adaptability to a wide range of applications.

This recognition led to the inception of Opus, a codec designed to be a versatile, open-source solution that could handle an array of audio needs.

Origins and Development of Opus Audio Codec

Opus is a product of the collaborative efforts of two organizations: the Xiph.Org Foundation and the Internet Engineering Task Force (IETF).

Xiph.Org Foundation: Xiph.Org, an organization known for its commitment to open-source multimedia, initiated the development of Opus. The team brought their experience and knowledge from projects like Vorbis (a predecessor in the audio codec arena) and other multimedia initiatives.

Internet Engineering Task Force (IETF): IETF is responsible for the standardization of Opus. Standardization is a vital step in the development of any technology, as it ensures interoperability and widespread acceptance. Opus became an IETF standard in 2012.

The collaboration between these organizations aimed to create a codec that would surpass its predecessors in terms of audio quality, versatility, and efficiency.

Technical Specifications of Opus Audio Codec

To truly understand the brilliance of the Opus codec, we must venture into its technical intricacies. At its core, Opus is a lossy audio compression format, but it achieves its remarkable flexibility and quality through a combination of innovative techniques.

Lossy vs. Lossless Compression

Before we dive into the specifics of Opus, let's clarify the difference between lossy and lossless compression. Opus falls into the lossy category, which means it compresses audio data by discarding some information that is considered less essential to human perception. While this might sound like a drawback, it's precisely this selective "loss" that enables Opus to achieve high compression ratios without perceptible degradation in audio quality. The goal is to strike a balance between reducing file size and preserving sound fidelity.

Bitrate and Quality Control

Opus offers a significant advantage in that it can operate over a wide range of bitrates, allowing content creators to choose the level of compression that suits their needs. This adaptability makes Opus suitable for applications where conserving bandwidth is crucial without compromising on audio quality.

Opus Architecture

At the heart of Opus lies its unique architecture, which combines elements of the CELT and SILK codecs. The codec uses a modified discrete cosine transform (MDCT) to analyze the audio signal in the frequency domain. This process essentially divides the audio signal into tiny segments, making it easier to compress.

Opus Frame Structure

Opus employs frames to organize audio data. Frames are chunks of audio that are processed individually. This structure allows Opus to maintain low latency, making it particularly well-suited for real-time applications like VoIP and video conferencing.

Variable Bitrate Encoding

One of Opus's standout features is its use of variable bitrate (VBR) encoding. Rather than allocating a fixed number of bits per second, VBR allows Opus to assign more bits to complex audio passages and fewer bits to simpler sections. This dynamic allocation optimizes audio quality while minimizing file size.

Error Resilience

Opus incorporates mechanisms to make it more robust against errors introduced during transmission. It employs techniques like forward error correction (FEC) and packet loss concealment (PLC) to ensure that even if some data is lost during transmission, the audio remains perceptually intact.

Psychoacoustic Modeling

Opus leverages psychoacoustic principles, which are based on the limitations of human hearing. By discarding audio data that is less perceptible to the human ear, Opus maximizes compression while maintaining audio quality. This intelligent modeling sets it apart from other codecs.

Dynamic Channel Count

Opus can handle variable channel counts, from mono to stereo and even surround sound. This flexibility is invaluable for applications like video conferencing and gaming, which require adaptive audio settings.

Opus vs. Other Codecs

Opus vs. MP3:

MP3, a widely recognized codec, was one of the pioneers of audio compression. While it offers decent sound quality, Opus outperforms it in several ways. Opus is designed to provide better audio quality at low bitrates, making it more suitable for modern applications where bandwidth efficiency is critical. Additionally, Opus is a more versatile codec, supporting a broader range of audio applications.  

Opus and MP3 are two popular audio codecs, but they differ significantly:

Opus:

1. Superior Quality: Opus offers exceptional audio quality with a wider frequency range.
2. Low Latency: Designed for real-time applications, Opus has low latency, making it ideal for online gaming and video conferencing.
3. Adaptability: Opus adjusts its bit rate dynamically, ensuring smooth audio even in varying network conditions.
4. Error Resilience: Opus handles data transmission errors better, resulting in more accurate audio decoding.
5. Multichannel Support: It supports multichannel audio for immersive experiences.

MP3:

1. Legacy Format: MP3 is a widely recognized but older codec.
2. Standard Quality: While good, MP3's audio quality is not as high as Opus.
3. Higher Bit Rates: MP3 files often have higher bit rates, leading to larger file sizes.
4. Less Suitable for Real-Time: MP3 may not be the best choice for real-time applications due to higher latency.

Opus vs. AAC (Advanced Audio Coding):

AAC is known for its high-quality audio, especially at higher bitrates. However, Opus surpasses AAC in terms of efficiency at lower bitrates. This is especially important for applications like streaming, where conserving bandwidth without compromising audio quality is essential.

Opus:

Outstanding Quality: Opus provides a broad frequency range of high-quality audio that can be used for voice and music among other applications.
Low Latency: Designed for real-time communication, Opus performs exceptionally well in VoIP calls, online gaming, and video conferencing.
Adaptability: Opus dynamically modifies its bit rate to provide uninterrupted audio transmission over a range of network situations.
Open Source: Opus is extensively used and available due to its open-source nature.
Multichannel Support: It is capable of handling surround sound and other multichannel audio for immersive experiences.

AAC:

Excellent Quality: AAC provides high-quality audio and is a standard format for music distribution and storage.

Efficient Compression: AAC's efficient compression maintains good quality with smaller file sizes, making it suitable for streaming and mobile applications.

Versatility: AAC supports a wide range of bit rates and profiles, making it suitable for a variety of applications, from low-quality audio streaming to high-fidelity music.

Widespread Compatibility: AAC is widely supported by media players, operating systems, and hardware devices, especially within Apple's ecosystem.

Enhanced Multichannel Audio: AAC supports multichannel audio, crucial for surround sound and home theater systems.

Opus vs. G.711 and Opus vs. G.729 (ITU-T Codecs):

These codecs are commonly used in VoIP applications. While they are known for their low latency, Opus offers a competitive advantage by delivering better audio quality while maintaining low latency. This makes Opus a preferred choice for real-time voice communication over the Internet.

Opus vs. G.711 (ITU-T Codec)

Opus:

1. Wide Usage Range: Opus is highly versatile and suitable for both real-time and non-real-time applications.
2. Exceptional Quality: It offers superior audio quality with low latency, making it ideal for online communication, gaming, and multimedia streaming.
3. Low Bitrate Adaptability: Opus adjusts its bit rate dynamically, optimizing audio quality according to available bandwidth.
4. Error Resilience: Opus is robust in handling network errors, ensuring accurate audio decoding.

G.711:

1. Narrow Usage Range: G.711 is primarily used in traditional telephony systems, with limited applicability in other modern applications.
2. Standard Quality: It offers standard audio quality but lacks the high fidelity of Opus.
3. Constant Bitrate: G.711 uses a fixed bit rate, making it less efficient for adapting to variable network conditions.
4. Limited Error Handling: G.711 is less resilient to network errors compared to Opus.

Opus vs. G.729 (ITU-T Codec)

Opus:

1. Versatile: Opus is suitable for various applications, from real-time communication to high-quality music streaming.
2. High Audio Quality: It offers superior audio quality and adaptability, making it well-suited for modern multimedia needs.
3. Low Latency: Opus has low latency, making it ideal for real-time applications like VoIP, online gaming, and video conferencing.
4. Error Resilience: Opus is robust in handling data transmission errors, ensuring smooth audio delivery.

G.729:

1. Narrow Usage Range: G.729 is primarily used in narrowband VoIP and telephony applications, limiting its versatility.
2. Good Quality: It provides good audio quality for its intended purpose, but Opus surpasses it in terms of audio fidelity.
3. Higher Bitrate: G.729 operates at a higher bit rate compared to Opus, potentially leading to increased bandwidth consumption.
4. Latency: G.729 has relatively lower latency, making it suitable for standard VoIP but less ideal for applications requiring ultra-low latency.

Opus vs. Vorbis:

Vorbis is an open-source audio codec often used in gaming and streaming applications. Opus outperforms Vorbis in terms of audio quality and compression efficiency, making it a more attractive option for developers looking to enhance the audio experience in their applications.

Opus:

1. Versatility: Opus is a versatile codec suitable for a wide range of applications, from real-time communication to high-quality music streaming.
2. Exceptional Audio Quality: It offers superior audio quality with a wide frequency range, making it a top choice for modern multimedia needs.
3. Low Latency: Opus has low latency, making it ideal for real-time applications like VoIP, online gaming, and video conferencing.
4. Adaptability: Opus dynamically adjusts its bit rate, optimizing audio quality according to available bandwidth.
5. Error Resilience: Opus is robust in handling data transmission errors, ensuring accurate audio decoding.

Vorbis:

1. Music and Multimedia Focus: Vorbis is primarily used for high-quality music and multimedia streaming, including audio compression for games.
2. Excellent Audio Quality: It offers excellent audio quality, making it suitable for lossy audio compression without significant perceptual quality loss.
3. Open Source: Vorbis is an open-source codec, ensuring accessibility and adaptability.
4. Lack of Real-Time Features: Vorbis is not designed for real-time applications like online gaming or VoIP due to higher latency.
5. Less Versatile: While high-quality, Vorbis is more specialized and may not be the best choice for applications requiring ultra-low latency.

Opus vs. FLAC (Free Lossless Audio Codec):

FLAC is a lossless audio codec, meaning it retains all the original audio data. Opus, being a lossy codec, sacrifices some audio quality for compression efficiency. The choice between the two depends on the specific requirements of the application. If you need lossless audio, FLAC is the way to go, but for scenarios where bandwidth or storage is limited, Opus provides a better solution.

Key Advantages of Opus:

Low Latency: Opus is renowned for its low latency, making it ideal for real-time applications like VoIP and online gaming.

Flexibility: It can adapt to a wide range of bitrates and provides excellent audio quality even at low bitrates.

Open Source: Opus is open source and royalty-free, which makes it accessible for developers and cost-effective for businesses.

Widespread Support: Many popular software and hardware platforms, including browsers, support Opus, ensuring seamless integration.

Efficiency: Opus excels at reducing data usage while maintaining high audio quality, a crucial factor in today's data-intensive world.

Use Cases and Applications of Opus Audio Codec

Voice over IP (VoIP): Opus is a staple in VoIP applications, providing crystal-clear voice communication with minimal latency. Whether it's a business conference call or a casual conversation with a friend over the Internet ensure that your voice is heard with the utmost clarity.

Video Conferencing: With the rise of remote work and virtual meetings, Opus has become a vital component in video conferencing platforms. It complements video streams with high-quality audio, enhancing the overall communication experience.

Streaming Services: Opus is well-suited for streaming platforms that deliver audio content over the internet. It excels in conserving bandwidth while maintaining exceptional sound quality, making it an excellent choice for music streaming, podcasts, and live radio broadcasting.

Gaming: Online gaming relies heavily on real-time communication, and Opus's low-latency capabilities make it a top choice for in-game voice chat. Gamers can coordinate strategies and socialize while enjoying the immersive audio effects of their favorite games.

Audiobooks and Podcasts: Opus optimizes the delivery of spoken word content, ensuring that listeners can enjoy audiobooks and podcasts with clarity and fidelity. It's particularly beneficial for long-form audio content.

Voice Assistants: Smart speakers and voice-activated devices depend on high-quality audio for accurate voice recognition and natural-sounding responses. Opus ensures that these devices provide a seamless and engaging user experience.

Live Broadcasting: Opus is widely used for live audio broadcasting, such as sports commentary and news reporting. Its low latency and exceptional audio quality keep audiences engaged in real-time events.

Public Safety Communications: Opus's low-latency and efficient data transmission capabilities make it a valuable tool for public safety and emergency communication systems. It ensures that critical messages are delivered promptly and clearly.

Multimedia Content Creation: Content creators, from YouTubers to filmmakers, use Opus to ensure that their videos have high-quality audio. It's an excellent choice for both recording and editing audio tracks.

Language Learning: Language learning platforms and applications use Opus to provide clear pronunciation and speech recognition features for learners. This aids in language acquisition and improves the learning experience.

Accessibility Tools: Opus enhances accessibility tools for individuals with hearing impairments. Real-time captioning and transcription services rely on Opus to ensure that spoken content is accurately converted into text.

Frequently Asked Questions about Opus Audio Codec

Q1. What is the Opus codec used for?

A: Opus can handle a wide range of audio applications, including Voice over IP, videoconferencing, in-game chat, and even remote live music performances.

Q2. Is OPUS a good codec?

A: Opus performs well at both low and high bit rates. In listening tests around 64 kbit/s, Opus shows superior quality compared to HE-AAC codecs, which were previously dominant due to their use of the patented spectral band replication (SBR) technology.

Q3. Is OPUS better quality than MP3?

A: MP3 is transparent at 192kbps. Opus is transparent at 128kbps. This makes Opus 33% more efficient than MP3 for high-quality audio, and it is even more efficient for very low bit rates. That's 33% less bandwidth used when streaming music, or 50% more music files in the same storage space.

Q4. What is Opus codec for WhatsApp?

A: An OPUS file is an audio file created in the Opus format (also called “Ogg Opus“), a lossy audio format developed for Internet streaming. It uses both SILK (used by Skype) and CELT codecs and supports variable bit rates from 6 kb/s to 510 kb/s.

Q5. Does YouTube use OPUS?

A: Generally, YouTube plays the highest quality audio unless your bandwidth is very restricted. I was given 720p video but still the highest quality audio (opus, format id 251).

Q6. Is OPUS good for audio?

A: OPUS performs well at low bit rates making it a great format to choose when transmitting to or from locations with sub-optimal internet speeds while maintaining high-quality audio. For example, OPUS is great for transmitting speech and music with minimal latency.

Q7. What is the best video codec for quality?

A: The best video codec for quality is likely H. 266, as it is well-equipped to handle even 4k HD videos with high compression rates. A decent alternative for Google's devices and platforms (YouTube, Android, Chrome) would be the VP9 codec.

Q8. Who created the Opus codec?

A: A royalty-free audio codec developed by the Xiph.Org Foundation. It supersedes their prior Speex and Vorbis codecs, previously recommended separately for human speech and for general audio, with a single unified codec.

Q9. Is OPUS free to use?

A: You can encode or decode Opus-compatible streams for any purpose at no cost.

Q10. Does Zoom use OPUS?

A: Zoom supports HD voice by using SILK and Opus voice codecs with advanced algorithms in noise suppression, acoustic echo cancellation, and gain control. We believe audio is critically important and will prioritize it over video in low-bandwidth situations.

Q11. Can an MP3 player play OPUS?

A: Unfortunately, very few media players recognize the OPUS format. You will need to use external applications like VLC Media Player because neither Windows nor Mac is able to open it. Primarily, the OPUS format is designed to facilitate the streaming of audio over the internet.

Q12. Which codec is better than AAC?

A: In brief, SBC is the most basic codec with the lowest bit rate and, therefore, the most basic sound quality. AAC and AptX are both steps up from SBC and are generally mainstream. AAC is the best you can do on Apple phones and tablets, while AptX is a step-up option on Android.