Audio track layouts
Which track carries what.
The broadcast track allocations in one place: the EBU R123 file-exchange layouts and R48 tape-era cases that delivery specs cite by number, the 5.1 channel-order trap, and where Dolby E sits. Layouts up to 8 tracks: R123 Table 1 also defines 12a to 12h and 16a to 16f, which aren’t covered here.
5.1 channel order: broadcast vs film
The single most common re-mapping mistake: the two conventions agree on channel 1 only.
Red cells differ from the broadcast order. EBU R123/R48 (and broadcast delivery generally) use L R C LFE Ls Rs; the film order is the common film/Pro Tools convention.
Track allocations
R123 Table 1 also defines 12- and 16-track families (multi-language, sport main/clean-effects splits) along the same patterns. Audio for file exchange should be 48 kHz, 24-bit, time-aligned with picture.
Broadcaster examples
From current delivery specifications. Always confirm against the commissioning spec for your delivery.
ITV (HD)
R48: 2a · R123: 4b4 or 16 channels; stereo only (5.1 not supported for ITV HD). Accepted layouts: R48:2a (stereo on 1–2) or R123:4b (final mix 1–2, M&E 3–4). Unused tracks: PCM silence. No SMPTE ST 2020 Dolby metadata track.
RTÉ (HD)
R123Up to 8 tracks: 1–2 programme stereo; 3–4 optional M&E or Dolby E; 5–6 optional Audio Description premixed with programme. Unused tracks carry silence. Follows EBU R123.
ZDF (HD)
R123-style allocationEven track counts 2–16: 1–2 Send L/R; 3–4 second language; 5–6 Audio Description; 7–8 Dolby E; 9–14 discrete 5.1 (L R C LFE Ls Rs); 15–16 by agreement.
Dolby E in two sentences
Dolby E packs a multichannel mix into what looks like a stereo PCM pair (6 channels at 16-bit, 8 at 20-bit), so a 5.1 mix can ride on two tracks of an 8- or 16-track master (in R123 layouts it appears as the “encoded MCA” pairs). It is data, not audio: play it as PCM and you get full-scale noise, which is why delivery specs are explicit about which tracks may carry it and why unused tracks must be true silence.
Why layouts are cited by number
Specs say “R48:2a” or “R123:4b” instead of prose because the allocation must be unambiguous for international exchange, the whole point of both recommendations. If a QC report flags your audio configuration, the fix is almost always moving content to the tracks the cited layout expects, not re-mixing.
Related: track layout verifier · loudness targets & gain · file header reader · audio sync calculator.