MLow: Meta's low bitrate audio codec

Perceived Audio Quality & Artifacts

• Many listeners find MLow clearly better than the Opus samples at very low bitrates, especially under loss.
• Others notice odd “glitchy” artifacts (e.g., voice sounding like a harp or harsh/unnatural), sometimes preferring Opus’s smoother but duller “tin can” sound at 6 kbps.
• Fascination with complex codec failure modes is noted (akin to video “datamoshing” and glitchy AI video).

Why <10 kbps Matters

• Several comments ask why ultra‑low bitrates are needed when LTE can support higher rates.
• Counterpoints: billions of users are still on 2G/3G, unstable or congested links, or extremely small data caps; lower bitrate means more talk time and more concurrent users.
• Low‑bitrate codecs are also critical for telephony backhaul, multiplexing many calls, and radio systems.
• Some are skeptical that a 10 kbps IP path is often “stable enough,” but others report real‑world use on low‑bandwidth, stable links and highlight the 30% packet‑loss demo.

Packet Overhead, Latency & VoIP Realities

• One line of argument: at typical RTP/UDP/IP overheads, header bytes dominate at these bitrates, limiting savings.
• Others respond that apps can bundle larger audio frames (e.g., >100 ms), use dynamic packet times, and voice activity detection to reduce packet rate, trading latency for bandwidth.
• Discussion of bufferbloat, fair queueing, and jitter shows that latency and loss behavior often matter more than raw bitrate.

Comparisons to Existing Codecs

• Several commenters criticize the lack of comparison with Codec2, Lyra/SoundStream, Speex, LPCNet, AMR‑WB, and classic G.729.
• Some point out that Opus was not designed to be optimal at extreme low bitrates and that Opus 1.5 with NoLACE and improved loss handling might narrow the gap.
• Robustness to bit errors versus packet loss is raised as important but not fully demonstrated; behavior under varying error models is described as unclear.

Openness, Patents & Availability

• Multiple people ask for source code, license details, and standardization plans; none are provided in the blog post.
• Concern that this becomes another IP‑encumbered codec, in contrast to patent‑free Opus; some wish Meta would donate it to an open standard to avoid patent thickets.
• As of the discussion, MLow appears to be an in‑house, production‑deployed codec with no public implementation.

Potential Applications

• Suggested uses include: WhatsApp/Messenger/Instagram calling and voice messages on poor networks, satellite and emergency voice (e.g., phone SOS), digital radio replacing AMBE, and dense backhaul links.
• Some are interested in creative uses: exploiting MLow’s artifacts for music, vocoder‑like effects, or intentional “glitch” processing.

Meta’s Motives & Reputation

• Many accept Meta’s claim that this is practical research to improve call quality and reduce data use for billions of users, especially in developing regions; internal metrics reportedly show higher engagement.
• Others remain wary of Meta: they praise its engineering and open‑source track record (LLMs, compression, frameworks) but argue this doesn’t offset broader criticisms (privacy, social harms).