p3i T4b

T4b is a small follow-up/hotfix release on top of T4a. It fixes a rare DTS case that could mute audio and adds a brightness boost for VS10's DV/HDR10→SDR conversion that actually works, plus a couple of smaller things. The work is mostly in Kodi and the kernel, with a bundled-skin bump and a German-translation resync alongside; coming from T4a, it's a low-risk update.

The headline changes:

• Fixed a rare case where DTS with dialnorm played silence on strict AVRs and soundbars (the T4a dialnorm defeat wrote a bad CRC).
• New "Boost VS10 SDR output brightness" control: DV and HDR10 converted to SDR no longer have to look dim, with an Auto mode that lifts as far as possible without clipping.
• New opt-in sub-setting to apply the green-flash hold to Dolby Vision only, so other content restarts without the brief blank.
• Smaller: bitmap-subtitle zoom down to 10%, and a full German (de_de) translation resync.

Highlights

1. Fixed a rare DTS-with-dialnorm case that could mute audio

T4a added DTS/DTS-HD/DTS:X dialnorm defeat (on by default), but the DTS-HD extension-substream header CRC was recomputed with a lookup table (AV_CRC_16_CCITT) that isn't compiled into Kodi's libavutil. The call returned garbage, so the rewritten header carried an invalid CRC. Strict AVRs and soundbars rejected the extension and played silence, while lenient decoders (and the offline validation, which used a correct CRC) were fine. So it was rare on two counts: it only hit strict decoders, and only on the uncommon DTS-HD / DTS:X titles that actually carry a dialnorm value in their extension substream. Frames without dialnorm never recompute the CRC, so they were never touched.

T4b computes the CRC itself (CRC-16-CCITT, poly 0x1021), and the output is byte-identical to a known-good reference stream. If DTS-HD MA went quiet for you on T4a, this is the fix. You can also just turn the defeat off under Settings/System/Audio.

2. Boost the brightness of DV/HDR10 → SDR conversion

DV and HDR10 tone-mapped to SDR through VS10 look dim next to the GUI and native SDR content. T4b adds a control that lifts it: "Boost VS10 SDR output brightness" (Settings/System/CoreELEC, under the DV settings: Off / Auto / Manual, default Off).

It works on the source side. The Dolby tonemapper builds its curve for the source's declared mastering peak, and most content never comes close to that number. All the headroom between the actual content peak and the mastering peak is picture range thrown away. Cap the declared peak and the tone curve spends the SDR range on picture instead.

• Auto assumes the source peaks at its actual content peak (MaxCLL) instead of the mastering display peak — the strongest boost that cannot clip, since the headroom above the content peak is unused by definition. For DV titles without an L6 metadata block it falls back to the base layer's HDR10 SEI CLL; with no usable peak metadata it does nothing.
• Manual sets a ceiling on the assumed source peak ("Maximum source luminance", 100–4000 nits). Titles below the ceiling keep the full no-clip Auto boost; brighter titles are treated as peaking at the ceiling, and their content above it clips. Lower is brighter. The ceiling is also used directly for titles without peak metadata, which Auto alone can't help.

HLG sources are not affected: the Dolby library substitutes its own internal peak assumption for HLG, so no lever exists on that path (proven on-device).

Validated on-device with Dunkirk (4000-nit mastering, 323-nit content peak): Auto lifts it, Manual 400 matches Auto, Manual 200 is brighter still. This control replaces the T4a "VS10 SDR target luminance" slider, which an on-device A/B proved the Dolby library ignores outright (10 and 4000 nits gave identical output); that setting could never work and is gone.

3. The green-flash hold can now be limited to Dolby Vision

T4a added an on-by-default black hold that hides the brief green flash on the video plane at the start of playback and on seeks. It blanks the picture through the decoder restart until the first clean frame arrives, which means a moment of black on every start and seek. T4b lets you apply that hold to Dolby Vision streams only, so everything else restarts without the blank. The new sub-setting is coreelec.amlogic.video.restart.mute.dvonly (default off, so nothing changes unless you turn it on); the seek-edge settle, which only runs while a hold is engaged, follows the same gating.

4. Also in T4b

• Bitmap subtitle zoom down to 10%. The minimum zoom for image-based (PGS/VobSub) subtitles drops to 10%, so oversized bitmap subs can be shrunk much further.
• German translations resynced. A full de_de resync against the current English strings, in both Kodi and the CoreELEC Settings addon. Kodi discards a translation when its stored English source no longer matches the live string, so after all the T4a/T4b setting reworks some German labels had fallen back to English — this brings them back.

Known issues

Changelog

Everything since T4a.

xbmc / Kodi (9 commits)

• 08e05ea953 Subtitles: allow bitmap subtitle zoom down to 10%
• bc189bc9aa Lang: de_de — full resync against en_gb
• 6c110988bf DV: SDR brightness boost — drop the HLG claims from the help texts
• fd16e005a0 DV: refresh the SDR brightness boost param on every DV engage
• 9ee4b773d4 DV: replace the dead VS10 SDR target nits with a source-peak brightness boost
• 4481df935b DV: VS10 SDR target nits — fix no-op param write, move below VS10 DV (superseded by the boost above)
• 7c5e6cbc53 AMLCodec: add a DV-only sub-setting for the green-flash video hold (default off)
• f5a1e63b05 DV: fix the VS10 SDR target nits setting never showing in the GUI (superseded by the boost above)
• 02169a0bd6 AEStreamInfo: fix DTS-HD MA dialnorm defeat muting audio (bad EXSS CRC)

Kernel (linux-amlogic, 3 commits)

• 07c0670d43 amdolby_vision: SDR boost auto — fall back to BL SEI CLL when L6 is absent
• d762ac4d9e amdolby_vision: add xbmc_dv_sdr_src_max_nits — source-peak cap to brighten →SDR
• 5e664b1a62 amdolby_vision: map extended source formats onto the target_lum_max rows

CoreELEC (distro)

• 9601b29c8d bump the bundled skin.p3i.estuary to 8.8.15
• 4644f095c1 update README, plus the T4b version marker

CoreELEC Settings addon

• 681031c lang: de_de — translate all missing German strings

Donations

Installation

1. Dirty

Drop the update tar into your CoreELEC update folder and reboot.

Should hitting reboot result in a black screen (long-standing issue with any build), wait 10 seconds to make sure this wasn't just a fluke, then unplug and re-plug the device's power. The upgrade will commence afterwards.

2. Dirty (safe)

Drop the update tar into your CoreELEC update folder, shut down the device, pull the power plug for 30 seconds, replug.

3. Flash

Use the provided Flash img.gz to prepare your SD card as you would with any other CoreELEC build.

Thanks

A massive shoutout to everyone involved in this build! Special thanks to the testers who flagged the DTS-HD MA audio dropout, and to nissel for the on-device A/B work that proved the old VS10→SDR target a dead end and then dialled in the new brightness boost. Upstream projects this builds on: avdvplus (DV metadata handling), libdovi, libass and FFmpeg, with eac3to as the reference for validating the DTS dialnorm output.

Full Changelog (Kodi core): https://github.com/pannal/xbmc/commits/T4b/
Full Changelog (Kernel): https://github.com/pannal/linux-amlogic/commits/T4b
Full Changelog (CoreELEC): https://github.com/pannal/CoreELEC/commits/T4b
Addon repo: https://github.com/pannal/p3i_repo

Contributors

Sources and contributors whose work landed in T4b (not exhaustive!):

• nissel — on-device VS10→SDR A/B testing (proved the target-nits path dead, validated the source-peak boost)
• Everyone who reported the DTS-HD MA silence
• CPM / avdvplus (R9) (@cpm-code) — DV metadata lineage
• eac3to — reference for validating the DTS dialnorm output
• libdovi / libass / FFmpeg — upstream projects

#CoreELEC p3i internal testing team: mad props to all of you not listed here. You made this possible. Thank you.