IAMF Basics
Requires Orbit 1.4 or later
IAMF playback was added in Orbit 1.4. If you're on 1.3 or earlier, IAMF files won't be recognised — update Orbit from the account portal to load them.
IAMF v2.0 is still a Working Group Draft
The IAMF v2.0 specification is, as of today (April 2026), an Alliance for Open Media Working Group Draft rather than a ratified standard. Orbit implements the v2.0 spec in full — everything on this page works today — but a small part of the spec could still shift before AOM approves it. In practice this is unlikely to change anything user-visible: if a final-spec tweak affects Orbit's decode, we ship a point release to match, and files authored against the draft open correctly in both. Files authored to v1.1 (already ratified) always work, regardless.
IAMF (Immersive Audio Model and Formats) is a newer spatial audio container designed for streaming. Where ADM BWF was built around the studio and delivery masters, IAMF was built around the decoder — it encodes the spatial structure next to coded audio (Opus, FLAC, AAC, or LPCM), so a file of tens of megabytes carries the same immersive mix a multi-gigabyte ADM BWF does. Orbit plays IAMF natively and routes it through the same speaker-first monitoring chain as ADM.
What is an IAMF file
IAMF is maintained by the Alliance for Open Media (the same group behind AV1). Files end in .iamf (raw bitstream) or .mp4 (IAMF wrapped in an ISO media container, optionally with video).
Inside, an IAMF file describes:
- Audio Elements — the spatial building blocks (see below).
- Mix Presentations — one or more authored mixes of the audio elements, each with its own gains, per-layout loudness measurements (integrated LUFS, true-peak dBTP), and optional language labels.
- Codec Configs — which codec the substreams use and how to decode them.
If you want deeper background, the canonical references are the v2.0 spec at aomediacodec.github.io/iamf and the v1.1 spec that preceded it.
The three Audio Element types
IAMF organises a mix into Audio Elements. There are three types, roughly parallel to how ADM splits content but with different names:
| IAMF term | ADM equivalent | What it is |
|---|---|---|
| Channel-Based element | Bed | Fixed-layout multi-channel audio (stereo, 5.1, 7.1.4, etc.) |
| Object-Based element | Object | Mono / stereo source with animated position and gain |
| Scene-Based element | Ambisonics group | Higher-Order Ambisonics (HOA) — spatial field encoded as spherical-harmonic channels |
You'll see IAMF's native vocabulary in Orbit's sidebar when an IAMF file is loaded ("Audio Elements", "Channel-Based", "Scene-Based"), and the ADM vocabulary when an ADM file is loaded ("Bed", "Object", "Ambisonics"). They describe the same underlying concepts.
Mix Presentations
An ADM programme describes one authored mix. An IAMF file can carry multiple Mix Presentations — different authored versions of the same content (e.g. a 7.1.4 mix and a stereo mix, or language variants) selected by the decoder at playback time.
Orbit loads all Mix Presentations the file declares and displays them in the sidebar. You can switch between them while the file is playing; each presentation's per-layout loudness measurements are shown inline.
Mix Presentations on export
Orbit Pro's ADM to IAMF export does not currently write multiple Mix Presentations — exported IAMF files carry a single Mix Presentation derived from the source ADM. Authoring multiple Mix Presentations on export is planned for a future release.
What Orbit does with an IAMF file
When you drop an IAMF file into Orbit, the pipeline is:
- Container demux — if the file is wrapped in MP4, the audio bitstream is extracted.
- Descriptor parse — audio elements, mix presentations, codec configs.
- Substream decode — per-element, per-codec. Opus / FLAC / AAC-LC / LPCM all supported.
- Layer reconstruction — scalable channel audio is reassembled; Scene-Based elements are demixed through their projection matrix (or direct-mapped in MONO mode) to produce HOA channels in ACN / SN3D order.
- Mix rendering — the selected Mix Presentation's gains and element summation are applied.
- Monitoring — the rendered content lands on Orbit's 7.1.4 speaker bus, from which binaural and stereo are derived.
From step 6 onward, IAMF plays exactly the same as ADM — same monitoring modes, same metering, same binaural chain. See Playback Approach for the speaker-first philosophy.
Codecs Orbit supports
All four codecs defined by IAMF v2.0:
| Codec | Status |
|---|---|
| Opus | Fully supported. The common choice for streaming IAMF. |
| FLAC | Fully supported. Lossless. |
| AAC-LC | Fully supported on macOS (via AudioToolbox). |
| LPCM | Fully supported. |
Orbit implements the IAMF v2.0 decode stack directly — it doesn't depend on the AOM reference decoder library.
Layouts Orbit can play back
Orbit's internal bus is 7.1.4, matching the ADM side. All standard IAMF loudspeaker layouts decode to that bus:
- Mono, Stereo, 5.1, 5.1.2, 5.1.4, 7.1, 7.1.2, 7.1.4, 3.1.2
- Binaural layout (as single-layer)
Expanded layouts (v2.0) not supported
IAMF v2.0 adds expanded loudspeaker layouts (9.1.6, 10.2.9.3, 7.1.5.4). Orbit does not currently support these — files that declare expanded layouts won't play back, and Orbit's ADM-to-IAMF export doesn't emit them either. If you're working with expanded-layout content and need to audit it, get in touch.
Scene-Based (HOA) playback
Since Orbit 1.4, Scene-Based audio elements decode end-to-end — both MONO mode (direct channel mapping) and PROJECTION mode (demixing matrix). The decoded HOA channels flow through Orbit's existing ambisonics pipeline — the same path used by HOA ADM content — so you get consistent 7.1.4 speaker feeds and binaural monitoring for both formats.
How IAMF differs from ADM in practice
- File size — IAMF with Opus is typically tens of megabytes where the equivalent ADM BWF is multi-gigabyte. Faster to load, faster to share.
- Mix Presentations — IAMF carries authored mixes; ADM carries one programme. If you're QC-ing an IAMF deliverable, part of the job is verifying every Mix Presentation, not just the "main" one.
- Loudness metadata — IAMF writes per-layout loudness measurements into the Mix Presentation. Orbit reads these and displays them; they're part of what a compliant IAMF file must include.
- Object vs Channel — more or less the same concept in both formats, but IAMF treats Scene-Based as a first-class type alongside channel-based and object-based.
Export (Orbit Pro)
Orbit Pro can encode ADM BWF content to IAMF with codec selection (Opus bitrate, FLAC compression, AAC bitrate, LPCM bit depth), per-object selection (which ADM objects stay as discrete IAMF objects vs get merged into the bed), Scene-Based (HOA) encode, and ISO-BMFF or standalone .iamf containers. See ADM-to-IAMF Exporting for the full workflow.
When you'd use IAMF
Use IAMF when you're delivering to a platform that plays IAMF natively. Today that includes Google's platforms (YouTube uses IAMF for its spatial audio streams) and Esfera, our own spatial audio streaming platform. More platforms are adopting it.
Practical uses:
- QC-ing a streaming deliverable before publishing
- Validating an encode against your ADM master
- Checking that your mix's per-layout loudness measurements land where you expect
- Distributing spatial audio outside the Dolby Atmos deliverable chain
Use ADM BWF when you're:
- Working from a studio master
- Delivering to Dolby Atmos certification workflows
- Receiving ADM BWF directly from a DAW
Both formats play through the same monitoring chain in Orbit, so moving between them day to day is friction-free.