v0.3.0 — Dolby Digital and DTS 5.1 over HDMI, and a lot more audio that used to be silent

0.3.0 — Dolby Digital and DTS 5.1 over HDMI, and a lot more audio that used to be silent

The headline: Passthru now sends the bitstream over HDMI as well as optical, so an
AV receiver decodes DD/DTS 5.1 straight from the HDMI port — no add-on board at all.
Alongside it, several classes of disc that previously played silent now have sound.

Dolby Digital / DTS 5.1 over HDMI (#25)

Audio Out = Passthru used to be optical-only, which meant an add-on board with an
optical connector — the Digital I/O board's TOSLINK, or the Analog I/O board's combo
3.5 mm mini-TOSLINK. It now also leaves over HDMI, which every MiSTer already has,
so 5.1 needs no extra hardware.

This works because a DD or DTS bitstream is an ordinary 2-channel 48 kHz stream
underneath — 1.536 Mbit/s, which is exactly why DVD caps DTS at 1509.75 — so it fits the
single I2S line the board wires to the HDMI transmitter. The chip is told the stream is
compressed via its channel-status registers.

Requires the custom Main (MiSTer_DVDcss), because only the ARM side can talk to the
HDMI transmitter over I²C. It engages automatically when your receiver's EDID advertises
AC-3 or DTS. If yours does not advertise it but you know it decodes, add to MiSTer.ini:

[DVD]
dvd_hdmi_bitstream=2

On stock Main, or on a TV that cannot decode these formats, HDMI stays silent rather
than making noise — verified on hardware.

⚠ Tested on a DE10-Nano only. DE10-Nano clones are copies of the same design and
should behave identically. SuperStation One is untested — it is a redesigned board
and we have not confirmed whether its HDMI transmitter is the same part, nor do we have
one to try. If you have one, reports welcome.

⚠ Passthru carries AC-3 and DTS only. IEC 61937 exists to carry compressed audio,
so an LPCM or MP2 track is silent in Passthru — on optical as well as HDMI. Use
Decode for those discs. This is a known gap rather than a permanent one: sending an
LPCM track as ordinary PCM is a supported thing for the hardware to do, it just needs
work on both the core and the Main side, so it is not in this release.

⚠ Multichannel LPCM is a different matter and is not possible on this hardware at
all: uncompressed 5.1 would need three more wires to the HDMI transmitter than the board
routes. Compressed 5.1 fits on one wire; uncompressed cannot.

Audio that used to be silent

• Every AC-3 channel layout now plays except 1+1 dual mono (#24). Mono (1.0) and the
  surround layouts 3/0, 2/1, 3/1 and 2/2 were silent before — a whole-disc silence on
  some titles, and a silent special feature on others.
• Passthru locks properly at the start of a title and across track changes (#26). It
  used to flap between naming the format and dropping out, sometimes needing a chapter
  skip to settle. This affected optical too, and predates the HDMI output.

Disc menus: LINK FAIL and options that all led to the same place (#23)

Probably the widest-reaching fix in this release. Many discs implement their menus by
routing every button through one shared destination, and having that destination
read back which button you pressed to decide where to go. The core was treating those
as dead ends, so every option led to the same place — or to LINK FAIL.

Reported as "doesn't let you enter the maze / picks Play All whatever you choose",
"navigation issues preventing progress", and "link failure on every menu option".

Measured against a 505-disc sweep:

• 178 discs (36%) contain the structure this fix addresses — a third of the library
  touches this code path
• 70 discs (14%) carry the strict dispatcher shape, one of them 171 times on a
  single disc
• 6 discs went from a hard boot failure to a working menu, with zero regressions
  across all 505. Four of those six were silently broken and had never been reported.

The prevalence number matters less than where it bites: the sweep could only measure
where a disc boots, and most of these dispatchers sit behind buttons you press while
using a menu. On a TV box set checked separately, the boot landing was fine while every
single menu button failed before the fix and worked after it.

Video

• Film detection no longer flaps on dark scenes (#22). Near-black frames carry no
  usable cadence evidence, and counting them could flip the detector mid-film. It now
  ignores uninformative frames. Measured across 123 discs: 15 better, none worse.

Tools

• DVD drive region tool (#27) — read a USB drive's region, and the remaining change
  count, from the Scripts menu. A drive with no region set makes every physical disc pay
  a multi-second CSS crack.
  ⚠ The SET path is untested on real hardware, and setting a region is irreversible
  (roughly five changes, ever). Reading is confirmed working. Treat setting as
  use-at-your-own-risk.

Also in this release

• Pre-release cleanup of the HDMI bitstream debug options (#29)
• Documentation corrections throughout (#28, #30), including a stale claim that AC-3
  layouts were unsupported after they had been implemented

Install

Extract to /media/fat. For CSS-encrypted media, physical discs, or HDMI bitstream, add:

[DVD]
main=MiSTer_DVDcss

and run install_dvdcss once from the Scripts menu.

The bare .rbf alone plays decrypted ISOs on stock Main, as before.