Meta has recently announced the Meta Low Bitrate (MLow) audio codec, aimed at improving real-time communication (RTC) on less advanced devices and slow internet connections. This codec is tailored to provide efficient and superior audio streaming capabilities, particularly in environments with limited bandwidth availability.
Optimized for scenarios where both low-latency and low-bitrate audio are essential—such as virtual meetings, gaming, and live broadcasts—MLow reportedly offers double the audio quality of the Opus codec (POLQA MOS 1.89 vs 3.9 at 6 kbps WB) and is 10 percent less computationally demanding.
Due to its lightweight nature, MLow is well-suited for mobile devices and platforms with restricted resources. It aims to minimize network congestion and delay in real-time communications. Jatin Kumar, Bikash Agarwalla, Sriram Srinivasan, King Wei Hor, and Tim Wong have stated the purpose as follows:
A substantial segment of our user base still operates on low-end devices. For instance, over 20 percent of our calls occur on ARMv7 devices, and tens of millions of daily calls on WhatsApp happen on devices that are more than a decade old. Given the existing range of codec options and our dedication to ensuring a superior call experience for all users, regardless of their device, there is a clear need for a codec that requires minimal computational power while still providing high-quality audio at the lowest bitrates.
Source: Meta blog
Enhancing either complexity or bitrate typically boosts the audio quality, however, modern codecs aim to push the quality further while considering the balance between complexity and bitrate. They achieve this by incorporating extensive insights into audio signal characteristics and applying psychoacoustic theories.
One of the hurdles is adoption: the last renowned, high-quality, open-source codec was Opus, which emerged in 2012. Kumar, Agarwalla, Srinivasan, Hor, and Wong explain:
MLow draws from the foundational principles of the traditional CELP (Code Excited Linear Prediction) codec but introduces improvements in excitation generation, parameter quantization, and coding techniques. (…) By optimizing split-band processing, MLow can encode the high band with minimal bits, enabling it to deliver SuperWideBand (32kHz sampling) at a significantly reduced 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, tackling the challenges posed by diverse devices and network environments. In a popular Reddit thread, user BlueSwordM comments:
This appears to be an impressive addition to the growing repertoire of low bitrate audio codecs. My concern with this initial article is the lack of specificity regarding which version of Opus was utilized at these lower bitrates as it’s unclear whether Opus 1.4 or Opus 1.5 was implemented. Given the advancements introduced in Opus 1.5 through new ML coding tools, its absence might lead to ambiguity.
User ggRavingGamer acknowledges the technological breakthrough but points out:
Ultimately, it may not matter, as the majority of podcasts and other content will likely continue using MP3 and AAC decades from now.
The new codec can be utilized across various platforms such as web development, mobile applications, and embedded systems.
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