Dolby MAT Dolby Metadata-enhanced Audio Transmission

What Dolby MAT is

Dolby MAT stands for Metadata-enhanced Audio Transmission, though some write-ups print "Transport." Pocket-lint calls it a container format rather than a new audio format, and it is best understood as a way to move audio across HDMI, not a codec. It began with Dolby TrueHD, whose bitrate varies as with any lossless format: a source packs the TrueHD bitstream into MAT frames and the receiver decodes it, and Pocket-lint describes the payload as raw PCM audio with metadata alongside. Wikipedia's TrueHD entry lists three ways to move TrueHD to a receiver: analog, 6 or 8 channel linear PCM over HDMI 1.1 or higher, or the original bitstream encapsulated in MAT frames over HDMI 1.3 or higher, and it calls MAT "the transport mode mandated by Dolby Atmos."

How MAT works

MAT 2.0 extended the idea to Dolby Atmos. Pocket-lint explains that raw audio travels as PCM while Atmos metadata tells the receiver how to render it, and the point is real-time performance: a source such as a game console can send decoded audio with metadata without re-encoding. A Dolby presentation from 2021 states the specifics: MAT 2.0 "is a solution to transmit more audio" via HDMI 1.4 and higher and via eARC in HDMI 2.1 and higher, and it carries up to 31 objects plus LFE and metadata. In Dolby's MS12 playback pipeline, the decoder output is PCM plus metadata, and MAT 2.0 is the PCM path to HDMI, ARC and eARC.

The payload sizes explain why eARC matters. Wikipedia gives eARC a bandwidth of 37 Mbps and support for up to 32 channels, adding uncompressed 5.1 or 7.1 PCM, Dolby TrueHD and DTS-HD Master Audio passthrough. The Blu-ray Disc Association lists the maximum Dolby Lossless (TrueHD) audio rate at 18.64 Mbps, about half of eARC's 37 Mbps (18.64 / 37 = 50.4%). Production Expert reports a 7.1.4 PCM render at 13,824 kbps (12 channels x 24 bit x 48 kHz), which uses 37.4% of the eARC link and leaves 23.2 Mbps free. ARC is far smaller: Wikipedia says it supports stereo PCM and compressed Dolby Digital, Dolby Digital Plus and DTS up to 5.1 channels, with Atmos metadata inside Dolby codecs.

MAT vs bitstreaming DD+ JOC and TrueHD

Streaming Atmos is Dolby Digital Plus JOC at 384 kbps minimum with 12 elements or 448 kbps with 16, per Hybrik, and Netflix raised its Atmos rate to 768 kbps in 2019. Dolby Digital Plus is among the codecs ARC supports, so a TV app can pass it to a soundbar as a bitstream. MAT is the alternative for devices that decode first. Pocket-lint notes the Apple TV 4K uses MAT for its Continuous Audio feature, a feature Apple promises will switch between audio formats without glitches, and that the Xbox Series X uses it too; Dolby's 2021 slide lists Xbox, Apple TV and the 2020 Roku 4K Ultra as MAT 2.0 sources. The trade-off, per Pocket-lint, is more reliance on settings and occasional decoding glitches. See bitstream vs PCM.

Where MAT lives

Dolby states MAT 2.0 is present in 100% of Dolby Atmos TVs, soundbars and AV receivers shipping as of that 2021 deck, and that it enables ATSC 3.0 audio compatibility, since a decoded Dolby AC-4 program reaches the receiver this way. Sonos soundbars show the failure mode: Pocket-lint says the Arc and Beam suffered occasional extremely loud "pop of death" artifacts when corrupt data was not filtered from the PCM stream, with a software fix in November 2023. Wikipedia lists the HDMI cables eARC needs: Ultra High Speed, Premium High Speed with Ethernet, or High Speed with Ethernet, so a 48 Gbps cable is not required just for eARC. Check the cable guidance in the HDMI cable guide and the HDMI cable tool.

Worked example: does the link have room?

When the TV is the audio source for a receiver, as with a TV app or a player plugged into the TV, the link is eARC at 37 Mbps. A Blu-ray TrueHD Atmos track tops out at 18.64 Mbps, which leaves 18.4 Mbps spare. A Netflix Atmos track at 768 kbps uses 2.1% of the link (0.768 / 37) and, being lossy DD+ JOC, also passes ordinary ARC. The studio-grade 7.1.4 PCM render in MAT form uses 13.824 Mbps, or 37.4%. Every format here has bandwidth headroom, so when Atmos fails to light up, a setting such as the TV's PCM mode or a cable is a likelier cause than capacity.

Common confusions

The most common is whether MAT needs eARC. Dolby's own slide says HDMI 1.4 and higher, and via eARC from HDMI 2.1; Pocket-lint says MAT depends on eARC and that HDMI 2.0 lacks the bandwidth. The two reconcile once you separate lossless from lossy: lossless TrueHD Atmos needs eARC's capacity, while lossy Atmos fits ARC. Pocket-lint also reports that a TV set to Auto or PCM can strip the Atmos metadata on its way to a soundbar, so force passthrough, and that MAT can flag a stereo mix as Atmos, which switches off a receiver's stereo upmixing. See eARC, Dolby TrueHD and DD+ JOC. For the setup side, read the Atmos setup guide.