Meta has recently announced the Meta Low Bitrate (MLow) audio codec, aimed at enhancing real-time communication (RTC) on low-end devices and slow-speed connections. This new codec is designed to deliver efficient, high-quality audio streaming, even under low bandwidth conditions.
MLow is optimized for use cases where low-latency and low-bitrate audio are required, such as online conferencing, gaming, and live streaming. According to the developers, the new codec achieves twice the quality of Opus (POLQA MOS 1.89 vs 3.9 at 6 kbps WB) while maintaining 10 percent lower computational complexity.
MLow is designed to be lightweight, making it suitable for mobile devices and other resource-constrained platforms, reducing network congestion and latency in real-time scenarios. Jatin Kumar, Bikash Agarwalla, Sriram Srinivasan, King Wei Hor, and Tim Wong explain the goal:
A significant number of our users still use low-end devices. For example, more than 20 percent of our calls are made on ARMv7 devices, and 10’s of millions of daily calls on WhatsApp are on 10-year-old-plus devices. Given the readily available codec choices and our commitment to ensure that all users – regardless of what device they’re on – have a quality calling experience, we clearly need a codec with very low-compute requirements that still delivers high-quality audio at these lowest bitrates.
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Source: Meta blog
Increasing complexity or bitrate usually improves audio quality, but the goal of new codecs is to achieve higher quality while balancing complexity and bitrate. This is accomplished by leveraging deep knowledge about the nature of audio signals and utilizing psychoacoustics.
Adoption is another challenge: the last widely known, high-quality open-source codec was Opus, released in 2012. Kumar, Agarwalla, Srinivasan, Hor and Wong add:
MLow builds on the concepts of a classic CELP (Code Excited Linear Prediction) codec with advancements around excitation generation, parameter quantization, and coding schemes. (...) With these split-band optimizations, we are able to encode the high band using very few bits, which lets MLow deliver SuperWideBand (32kHz sampling) using a much lower bitrate.
Srinivasan, Kumar, and Agarwalla recently presented a session on how Meta manages natural real-time audio communication at scale across WhatsApp, Instagram, and Messenger, addressing the diversity of devices and network conditions. In a popular Reddit thread, user BlueSwordM writes:
This looks like a new great addition to the ever-growing library of low bitrate audio codecs. My only issue with this introductory article is that they don't seem to specify which Opus version was used at these low bitrates: we don't know if Opus 1.4 or Opus 1.5 was used. Considering the improvements Opus 1.5 brought to the table at these low bitrates with new ML coding tools, it is slightly misleading.
User ggRavingGamer highlights the technical achievement but warns:
It doesn't matter, most podcasts, most anything will still use MP3 and AAC in 20 years.
The new codec can be used in different applications, including web development, mobile apps, and embedded systems.