p3i T4a

T4a is a focused follow-up to T4. It is mostly bug-fixes and a batch of new audio and Dolby Vision tuning, on top of everything T4 already shipped. If you are coming from T3b or earlier, read the T4 notes first — this release builds straight on them.

The headline changes:

• A whole new set of audio controls: AC3/EAC3 dynamic range compression, DTS/DTS-HD/DTS:X dialnorm defeat, a finer centre-channel boost, LFE downmix up to 300%, and LAV Full is now the default passthrough sync mode.
• Fixed decoded AC3/EAC3 jumping louder after a seek and staying that way (the decoder's range compression was switched off on the first seek).
• A new toggle (on by default) that gives audio the same DDR-bus priority as video, closing a rare split-second HDMI dropout under heavy 4K/Dolby Vision decode.
• Several playback glitches gone: the post-seek picture freeze, the pause/resume video wedge, and the green flash at the start of playback and on seeks.
• The display-synced video clock now recovers from a vsync stall on its own (no more black-screen-with-audio), and its on/off toggle is finally live — in T4 the setting needed a reboot to take effect once it had been on for a single playback.
• New seek-back recall for embedded text subtitles: the line that should be on screen at the seek target shows up right away, instead of staying blank until the next event.
• More Dolby Vision tuning: an adjustable SDR target brightness for DV/HDR tone-mapped to SDR via VS10 (it used to come out dim), a CMv4.0→CMv2.9 down-convert for older DV TVs, a Smart CMv4.0 mode (now the default on Display-LED), and auto-letterbox for cropped DV.
• Dual-track Dolby Vision .mp4 files now play the right stream instead of just the enhancement layer.
• Skin reloads now announce themselves, giving add-ons the hooks to avoid the UI freeze a background skin update could otherwise cause (upstreamed to Kodi).
• On a 4K display, the GUI desktop now defaults to 1080p instead of 2160p50/60, sidestepping an HDMI link-budget sync issue some AVR chains hit in the menus (your saved screenmode and the video whitelist are unaffected).
• Under the hood: FFmpeg 8.1.2, zram swap-in tuning, and a refreshed default skin.

Highlights

Roughly ordered by how many people each change affects, and how visible it is.

1. Audio: a batch of new controls and fixes

The biggest cluster of new work in T4a. Most of this came straight out of reporter requests.

• Fewer HDMI audio dropouts under heavy decode. On Amlogic the audio DMA shares a DDR-bus port that sits below the display and the video decoder in priority, so a peak 4K/Dolby Vision frame can briefly saturate memory bandwidth, starve the small audio FIFO, and make the AVR throw a split-second dropout. A new "Prioritise audio on the system DDR bus" toggle (Settings/System/Audio, on by default) raises that port to super-urgent for all audio — the same priority the display reader and video decoder already have, so audio is lifted to match video, not ahead of it. Audio is a fraction of a percent of DDR bandwidth, so it costs video playback effectively nothing. This is the clean, user-controllable replacement for the kernel-side DDR-arbiter tuning T4 experimented with (now reverted).
• Dynamic range compression for decoded AC3/EAC3. A new "Dynamic range compression (AC3/EAC3)" slider (Settings/System/Audio, 0–100%, default 100% = unchanged). Decoded AC3/EAC3 always had FFmpeg's full compression baked in with no way to dial it back from the GUI; now you can. Pull it down for a flatter, more faithful track, or leave it at 100% for the old behaviour. It is a no-op for codecs that carry no FFmpeg DRC control (DTS/AAC).
• Fixed decoded AC3/EAC3 getting louder after a seek. This is the one vlix and Daffietje kept hitting: a track started out correctly compressed, then on the first seek stepped up to its full uncompressed level and stayed there for the rest of playback (not a runaway climb — one jump, then sustained). FFmpeg's decoder flush quietly zeroes the compression scale on every seek; T4a re-applies it after each flush, so the level stays put. (Long-standing FFmpeg behaviour, not a p3i regression — it was just never adjustable before the new DRC setting above.)
• DTS dialnorm defeat for passthrough. A new "DTS dialogue normalisation defeat" toggle (Settings/System/Audio, on by default) forces dialnorm to 0 dB in DTS, DTS-HD HRA/MA and DTS:X passthrough bitstreams, so your AVR plays them at full reference level instead of the attenuation the stream carries. It joins the AC3/EAC3/TrueHD defeats already in the build, and only touches packings it recognises — a CRC self-check leaves anything unexpected alone. Validated against eac3to on real DTS-HD MA streams.
• Finer centre-channel boost. The centre-channel downmix boost now steps in 0.5 dB increments (0–30 dB) instead of whole dB, on a slider.
• LFE in the downmix can now go up to 300% for extra bass, up from the previous 100% ceiling. And in the "Front L/R" LFE target, the LFE now folds in at the same −3 dB as the default downmix, so the slider means the same thing in both modes and the bass stays balanced with the surrounds. The downmix matrix in that mode also honors the centre boost, the surround mix levels from the stream, and normalization — all of which it used to silently ignore.
• LAV Full is now the default passthrough audio sync mode (the setting is renamed from "Audio Fixes mode" to "Passthrough audio sync mode"). It is the validated path for the hardened TrueHD MAT packer and the vsync clock-sync work, and it gives the tightest lip-sync. The setting's help now spells out the options: LAV Full (recommended default), LAV SB (for seamless-branch discs only), and Off (stock Kodi). The TrueHD packer also picked up a few correctness fixes (negative-padding carry, counter unwrap, and a 96/192 kHz seamless-branch padding fix).
• Extra HDMI PCM layouts (4.0/5.0). Adopting CPM/avdvplus's approach, the Amlogic HDMI driver can advertise exact 4.0 / 5.0 channel allocations for multichannel PCM output, so the AVR reports the real layout instead of a padded 5.1. A new "Extra HDMI PCM layouts" toggle (Settings/System/Audio, default off) enables it; it takes effect on the next playback, no reboot. G12B/SC2-class boxes.

2. Fewer playback glitches: freezes, wedges and the green flash

A run of fixes for things that interrupted playback. These affect everyone, not just a particular content type.

• Post-seek picture freeze fixed. On some seeks the picture would freeze (audio carried on, the screen black-flashing every few seconds) and only another seek would recover it. The root cause was an ancient upstream bug: when neither stream had a real timestamp yet right after a seek, Kodi pinned its master clock to 0, starved the decoder of buffers, and fell into a reset loop. T4a waits for a real timestamp (a few frames, bounded to 2 s) instead of pinning to 0.
• Pause/resume video wedge fixed. Pausing high-bitrate 4K HEVC could wedge the video for ~17 s on resume (audio and the clock kept running, video fell behind then fast-forwarded to catch up). T4a detects that wedge directly and clears it with a quick internal re-seek, so playback resumes cleanly in about 2 s.
• The green flash is masked. That brief green rectangle/flash on the video plane at the start of playback and on seeks is an inherited Amlogic decode-restart race. A new "Mask green flash on video restart" toggle (Settings/System/CoreELEC, on by default) holds the output black through the decode restart until the first real frame lands. For the rare stream that still shows a torn green frame right at the seek edge, an opt-in sub-setting adds a one-or-two-frame settle (off by default, since it costs a few tens of milliseconds per seek and most streams don't need it).
• Green OSD on Back→replay fixed. Replaying a Profile-7 FEL Dolby Vision title without stopping first could show ~6 s of black video with a green OSD; the drain now returns immediately when nothing has been fed since the codec reset.

3. Embedded text subtitles: seek-back recall

The new feature here is seek-back recall for embedded text subtitles (ASS/SRT/mov_text/WebVTT), mostly off reports from nissel. Image-based subtitles (PGS/VobSub/DVB) and external subtitle files are unaffected.

• The line active at a seek target is recalled. A subtitle that should be on screen at the seek target is normally muxed before the keyframe the demuxer lands on, so it would otherwise not appear until the next line — sometimes a long wait with a large GOP. T4a caches the selected text subtitle as it plays and re-emits the right line at the target. This costs no extra I/O and is always on. For seeking into never-played territory there's an optional file-fallback (coreelec.subtitles.recallfromfile, default off) that reads the active line from the file, carefully budgeted so it can't stall playback.
• And lines no longer go blank after a backward jump. This part was a T4-era regression: with libass updated to master in T4, it pruned upcoming lines against a stale pre-seek clock and deleted events it would never re-read, so subtitles could go blank for ~30 s (proportional to the size of the jump). The libass track is now flushed on each seek and that faulty pruning is gone, so lines re-render correctly.

4. Dolby Vision: brightness, conversion and cropping tuning

• Adjustable VS10→SDR brightness (issue #59). DV/HDR content tone-mapped to SDR through VS10 looked dim next to the GUI and native SDR files, because the kernel hardcodes the SDR target to 100 nits. A new VS10 SDR target luminance slider (100–500 nits, default 100 = unchanged) lets you map for your panel's real SDR brightness.
• CMv4.0 → CMv2.9 down-convert for older DV TVs. Some older CMv2.9-only DV TVs black-screen (no OSD) on CMv4.0 content because they fail to fall back. A new opt-in setting strips the CMv4.0 extension blocks from each frame, leaving a clean CMv2.9 stream the older set can lock onto. It is the inverse of T4's CMv4.0 append and mutually exclusive with it.
• A "Smart" CMv4.0 append mode, now the default. On top of the existing Off/Always append modes, Smart decides per frame: it appends CMv4.0 where it helps, but bypasses it (and lets the TV use the native CMv2.9 dynamic metadata) when the frame's actual peak already sits comfortably above your display's capability, with an adjustable headroom threshold. It is now the default on Display-LED setups (the Always default and the auto-preset both move to Smart).
• Auto-letterbox for cropped DV. Cropped DV encodes (bars removed, e.g. 3840×1600) could show grey letterbox bars when the DV trim carries a high positive lift. T4a synthesizes the active-area geometry from the coded aspect and issues correct DV L5 metadata for the TV to handle the bars. It's pure geometry (the border detector is never engaged), gated to non-16:9 native DV, on by default, and a manual L5 override still wins. It's now its own setting, independent of the other L5 controls.
• VS10 SDR8/SDR10 output defaults back to Bypass. VS10's SDR→SDR path measurably clips whiter-than-white detail, and the smoother pacing it once seemed to lend is now provided by the real vsync clock instead. VS10 SDR stays available as an opt-in.

5. Dolby Vision: multi-track .mp4 files play the right stream

A dual-track dual-layer (DT-DL) Profile-7 Dolby Vision .mp4 carries its base and enhancement layers on two separate tracks. Kodi only knew how to combine them in MKV files, so an .mp4 ended up playing only the enhancement layer (and mislabelling itself "ST-DL"). T4a recognises the enhancement layer by its Dolby Vision config and combines the two correctly, while still leaving genuinely independent DV streams alone. (This complements T4's multi-video-track work, which let you select the extra streams in the first place.)

6. Dolby Vision: stability fixes

A set of fixes for hangs, color corruption and a settings glitch, mostly from on-device reports.

• Back→replay deadlock fixed. Hitting Back and replaying a DV title could freeze the picture on a lock-ordering deadlock between the DV-core lock and the GUI graphics lock. The locking is reworked, the DV-core sysfs is serialized behind a single recursive mutex, and a watchdog now names the blocked path instead of failing silently.
• DV→DV switch color corruption (gray/green) when one title was switching while another played in the background: the stale title's stop handler no longer reconfigures the DV core over the live stream. (For most setups the green-flash hold from highlight 2, on by default, also covers the brief blip this could leave.)
• "Reset to default" no longer needs two clicks. The DV/HDR TV preset used to stay on Manual after the first reset and only land on Auto on the second; a deferred recompute was flipping it back. It now sticks on the first click.
• VS10 no longer corrupts software-decoded video. VS10 conversion is a hardware-video-layer feature. On the occasional stream the Amlogic decoder declines (small MPEG-4/XVID, decoded in software), engaging it pushed plain SDR pixels through the DV core and turned the picture magenta/yellow. T4a recognises the software-decode path and keeps VS10 in Bypass there, and the live VS10 toggle now declines the conversion modes on such content (with a brief toast) — so the corruption can't happen.
• A GUI-path HDMI link watchdog and extra transition instrumentation went in to chase the remaining AVR-side blackout reports.

7. The display-synced video clock: a live toggle, stall recovery, tighter sync

T4 introduced the first real display-synced video clock. T4a hardens it on several concrete fronts.

• The "use display as clock" toggle is now live. In T4 the CoreELEC setting was read only once, at the first player startup — so after it had been on for a single playback, flipping it (on or off) silently did nothing until you rebooted. T4a applies it immediately (a brief A/V glitch is possible if you flip it mid-playback). The clock thread also only runs during video playback now, instead of polling the framebuffer the whole time Kodi sits idle in the GUI.
• Recovers automatically from a vsync stall. This is the one you'd actually notice: if the kernel's vsync wait stalls (a VPP reconfig on a seek, a mode switch, a wedged sink), the clock used to ride it down and the picture could go black for seconds with audio still playing, recovering only on stop. It now drops to legacy timing within ~750 ms and probes its way back as soon as vsync returns.
• Frame-accurate A/V corrections at matched rates. An inverted gate meant the frame-quantized clock corrections were running exactly when they shouldn't and disabled when they should. With the real vsync clock now driving things, the upstream behaviour is restored: on matched rates (24@24, 25@50, 60@60) an A/V correction becomes one clean frame dup/drop instead of an arbitrary clock lurch, and lip-sync under LAV Full is held to a tighter window.

8. Add-ons can survive a skin reload

A skin reload (usually a background skin-addon auto-update that calls ReloadSkin) tears down and rebuilds every window. An add-on sitting in a modal window at that moment (PM4K, for instance) can be left spinning over a destroyed window with nothing to react to, and the UI freezes until a full Kodi restart. T4a fires GUI announcements around the reload (OnSkinUnloading, then OnSkinLoaded, or OnSkinLoadFailed on the dead-end paths) that an add-on can subscribe to, so it can close or restart its own windows in time. The add-on has to implement these to benefit; it isn't automatic, and one that ignores them can still freeze. But the hooks are now there. A failed reload of a non-default skin also falls back cleanly to the default instead of leaving nothing loaded. The change is upstreamed to Kodi as xbmc/xbmc#28431.

9. 3D MVC subtitle depth

3D MVC (frame-packed Blu-ray) PGS subtitles used to render flat, at zero depth. T4a carries the per-stream 3D subtitle plane through to the decoded picture, so the subtitle now sits at the correct stereoscopic depth.

10. New default skin, refreshed

skin.p3i.estuary (vlix's Estuary variant, the default since T4) moves from 8.8.8 to 8.8.15 with a batch of presentation work:

• Codec logos on the startup toast and info: configurable layout and position, dark-themed variants, and an option (on by default) to keep them inside the DV active area so they don't land in the letterbox bars — using the new resolution-independent aspect class the player now exposes.
• A richer Player Process Info: new video-output detail (including Player-Led DV/HDR10), a subtitle section that scrolls long names, an audio-channel-layout fix, and info for the new CMv4.0 → CMv2.9 feature.
• A new option to hide the progress bar on pause and/or on seek.
• CoreELEC power-button and calibration icons.
• Fixed overlapping music-video media flags.

11. The p3i addon repository keeps growing

The pre-installed repository.p3i (served at p3irepo.pm4k.eu) picked up:

• inputstream.ffmpegdirect and inputstream.adaptive re-versioned under a 666.<upstream>-p3i.1 epoch so they cleanly update over the stock add-ons.
• script.module.jurialmunkey 0.2.35, the dependency for our plugin.video.themoviedb.helper build.
• A texture-packed variant of skin.p3i.estuary for faster repo installs.

12. The GUI desktop defaults off 2160p50/60

A 2160p50/60 desktop doesn't make the menus any sharper — Kodi renders the GUI at 1080p or below and hardware-scales it — but it does drive the HDMI link to its 594 MHz ceiling (4:2:2/12-bit deep colour). A marginal AVR/repeater chain, or a near-limit cable in a long run, can fail to lock onto that and keep dropping sync while you sit in the menus. So when your display's native mode is 2160p50/60, T4a now points the desktop at the 1080p entry at the same refresh rate by default. This only changes the out-of-the-box default: an explicitly chosen 2160p50/60 screenmode still wins, the mode stays in the list for manual selection, and the whitelist still switches to 2160p50/60 for genuine 50/60fps 4K video. The Resolution / Refresh rate / Whitelist help text was reworded to explain the trade-off.

13. Under the hood

• FFmpeg 8.1 → 8.1.2. A point release rolling up the PixelSmash fix plus the usual demux/decode hardening (mpegts, matroska, mov, hevc/h264, swscale). No API/ABI change; all our patches re-verified with zero rejects.
• zram swap-in tuning. With zram swap active, the kernel's read-ahead (page-cluster) is set to 0 — zram has no seek cost, so read-ahead only added decompression latency. Overridable via /storage/.config/zram.conf. (Closes #63.)
• Reverted the experimental audio DDR arbiter / HBR QoS kernel tuning T4 introduced, in favour of the user-controllable DDR-priority audio toggle (highlight 1).
• libdovi gained the dovi_rpu_remove_cmv40_metadata primitive (source-patch + prebuilt rebuild) behind the new CMv4.0→CMv2.9 down-convert.

Known issues

Changelog

The complete per-component commit list since T4. Click any section to expand.

Installation

1. Dirty

Drop the update tar into your CoreELEC update folder and reboot - this can be used as a dirty upgrade from CPM A14 or any of the U3k, avdvplus and earlier p3i (T1–T4) builds.

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.

Reset Settings/System/CoreELEC, reboot.

2. Dirty (safe)

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

Reset Settings/System/CoreELEC, reboot.

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 and reporters who chased down the seek-louder audio bug, the post-seek freeze and pause/resume wedge, the vanishing and doubled subtitles, the two-click TV-preset reset, and the audio-mix requests — and to the upstream projects this builds on: avdvplus (DV metadata handling), LAV, libdovi, libass and FFmpeg.

Full Changelog (Kodi core): https://github.com/pannal/xbmc/commits/T4a
Full Changelog (CoreELEC-Settings): https://github.com/pannal/service.coreelec.settings/commits/T4a
Full Changelog (Kernel): https://github.com/pannal/linux-amlogic/commits/T4a
Full Changelog (CoreELEC): https://github.com/pannal/CoreELEC/commits/T4a
Addon repo: https://github.com/pannal/p3i_repo

Contributors

Sources and contributors whose work landed in T4a:

• vlix — skin.p3i.estuary updates (codec logos, info), and the LFE / DRC audio reports and requests
• SamuriHL — Smart CMv4.0 L1-frame-peak fix (PR #27), LAV Full validation
• manuelh — centre-channel boost and Front L/R LFE downmix requests (#58)
• Daffietje — decoded-AC3 seek-louder report
• nissel — embedded-subtitle seek-recall reports
• ADAlvarez — two-click TV-preset reset and cropped-DV reports
• CPM / avdvplus (R9) (@cpm-code) — DV CMv4.0 / metadata lineage, and the 4.0/5.0 HDMI PCM-layout approach
• LAV / dovi_tool / libdovi / libass / FFmpeg — upstream projects