fix(mediaplayer): recover H.264 frame size on a mid-stream join over TS/RIST and RTMP (#969)

## Summary

Video over MPEG-TS/RIST and RTMP could fail to play after a mid-stream
join, erroring out with a 0x0 frame size ("video track ... announced no
frame size"). The TS/RIST and RTMP demuxers read the frame dimensions
from the first access unit they saw and then latched the announced
format. On a live join between keyframes that first AU carries no SPS,
so they announced 0x0, the decoder refused to configure, and the SPS in
the following keyframe was never read.

- `basis_ts.c` (TS/RIST): for H.264, hold the format announce until an
access unit actually carries an SPS with valid dimensions, dropping the
undecodable pre-IDR AUs and waiting for the next keyframe.
- `basis_rtmp.c`: drop media that arrives before the avcC sequence
header rather than announcing 0x0 (RTMP always carries the SPS in that
header).
- `basis_win_decode.cpp`: the no-frame-size diagnostic now names the
actual codec and states the observable failure, instead of always
attributing it to H.265.

RTSP is unaffected — it takes its dimensions from the SDP parameter sets
before media flows.

Windows x64 DLL and Android arm64 `.so` rebuilt (RIST-enabled).

## Required checks
All boxes below must be ticked before this PR can merge. If a check is
genuinely N/A, tick it anyway and explain under **Notes**.

<!-- required-checks-start -->
<!-- Tick the boxes in place — do not edit the line text. The
pr-checklist workflow parses this block; per-PR context goes under
Notes. -->
- [x] **Tested** — I built and ran this locally. The change works in the
editor and (where relevant) in a built player.
- [x] **Transform access is combined and limited** — In hot paths,
transform reads/writes go through `TransformAccessArray` or are
otherwise batched. I have not added per-frame `transform.position` /
`transform.rotation` / `transform.localPosition` calls inside loops.
Whenever I need both position and rotation, I use the combined APIs —
`SetPositionAndRotation` / `SetLocalPositionAndRotation` for writes,
`GetPositionAndRotation` / `GetLocalPositionAndRotation` for reads —
instead of two separate property accesses; the combined call does one
local-to-world matrix traversal instead of two.
- [x] **Addressables used for asset/memory loading** — Any new asset
loads go through Addressables. No new `Resources.Load`, no direct asset
references that pull large content into memory on scene load.
- [x] **No new `GetComponent` / `AddComponent` where avoidable** — Where
unavoidable, the result is cached on a field, and any `GetComponent<T>`
is replaced with `TryGetComponent<T>(out var x)` — bare `GetComponent`
will be denied. `TryGetComponent` is the modern API (Unity 2019.2+) and
skips the Editor-only GC allocation `GetComponent` causes when a
component is missing: Unity wraps the `null` return in a managed "fake
null" object so its overloaded `==` operator can still detect destroyed
C++ objects, and constructing that wrapper allocates; `TryGetComponent`
returns a `bool` plus `out` parameter and never builds the wrapper. None
of these calls run inside `Update`, `LateUpdate`, `FixedUpdate`, jobs,
or other per-frame code paths.
- [x] **Per-frame work is scheduled through `BasisEventDriver`** — Any
new per-frame work hooks into `BasisEventDriver` rather than adding
standalone `Update` / `LateUpdate` / `FixedUpdate` callbacks on a
MonoBehaviour.
- [x] **Anything added to `BasisEventDriver` is bulletproof, or guarded
by `try`/`catch`** — `BasisEventDriver` runs the single per-frame tick
that drives the whole framework (network apply, local player sim,
blendshapes, JigglePhysics, nameplates, and more) as one sequential
chain. An unhandled exception anywhere in that chain aborts the rest of
the tick, so every step after the throwing one is silently skipped for
that frame. New work added to the driver must either be guaranteed not
to throw, or be wrapped in a `try`/`catch` that contains the failure and
surfaces it through `BasisDebug` — logged once / rate-limited, never
every frame (see the existing `HVRBasisBuiltInAddresses.Simulate()`
guard for the pattern). Expect this to be scrutinized closely in review.
- [x] **Considered jobification** — I asked whether this work can be
moved to a Unity Job (Burst-compiled where possible). If it can, it is.
If it cannot, the reason is in **Notes**.
- [x] **No needless `{ get; set; }` properties or access lockdowns** —
Public fields are fine; Basis is meant to be read and modified freely,
so don't wall things off `private`/`internal` without a real reason.
Don't wrap a field in `{ get; set; }` when the accessors do nothing —
property accessors have a real performance cost vs direct field access,
and the lead maintainer prefers plain fields (or a method / setter-only
property when only the setter needs logic) over a noop-getter pair. For
`.Instance` singletons, callers reassigning `Type.Instance` is allowed;
if that would break your code, log a warning or throw — don't block the
assignment. Locking down access is not your call.
- [x] **Camera access goes through `BasisLocalCameraDriver`** — Code
that needs the local camera (transform, projection, rig data, etc.)
pulls it from `BasisLocalCameraDriver` rather than looking one up
itself. Don't roll a separate camera discovery path.
- [x] **Logging uses `BasisDebug`** — All new logging calls go through
`BasisDebug.Log` / `BasisDebug.LogWarning` / `BasisDebug.LogError` (with
an appropriate `LogTag`) instead of `UnityEngine.Debug.Log` /
`Debug.LogWarning` / `Debug.LogError`. `BasisDebug` routes through
Basis's tagged, color-coded logger and respects the project-wide
`LoggingDisabled` toggle so logging can be killed at runtime; bare
`Debug.Log` calls bypass that and will be denied.
- [x] **No scene-wide discovery for dependencies** — New code is
architected so it does not need `FindObjectOfType` / `FindObjectsOfType`
/ `GameObject.Find` / `FindGameObjectsWithTag` to locate what it depends
on. References are wired in — registered through an existing
manager/driver, injected at init, or passed in by the caller — rather
than discovered by scanning the scene at runtime. If a scene scan is
genuinely unavoidable, justify it under **Notes**.
- [x] **No allocations in hot paths** — Per-frame code (Update /
LateUpdate / FixedUpdate, simulation loops, jobs, anything called once
per frame or more) does not allocate. No `new` on reference types, no
LINQ, no `string` concatenation/interpolation, no boxing, no `foreach`
over interface-typed collections. Allocate once at init and reuse the
buffer.
- [x] **No debugging in hot paths** — No log calls of any kind on
per-frame paths, including `BasisDebug`. Hot-path logging floods the
console and incurs cost on every frame regardless of whether the message
is filtered out downstream. If a hot-path log is needed while iterating,
gate it behind `#if UNITY_EDITOR` and remove (or leave gated) before
merge.
- [x] **Hot-path collection access is optimized** — Cache `.Count`
(lists) / `.Length` (arrays) into a local `int` before the loop instead
of re-reading the property each iteration. Prefer `T[]` (with a separate
length int when the array is over-sized) over `List<T>` where the data
is hot — Unity's mono BCL doesn't expose
`CollectionsMarshal.AsSpan(List<T>)`, so a list can't be fed into
`Span<T>` / unsafe paths cleanly. Where the perf justifies it, drop into
`Span<T>` / `ref` locals / `Unsafe.As` / `unsafe` pointer code to skip
bounds checks and copies, and call out the invariants you're relying on
under **Notes** so reviewers can sanity-check them.
<!-- required-checks-end -->

## Testing details
Tick the platforms you actually tested on. Leave the rest unticked —
these are informational and do not block merge.

- [x] Windows
- [ ] Linux
- [ ] Android
- [ ] iOS
- [ ] macOS

Input / control mode coverage:

- [ ] Tested in VR (note headset under **Notes**)
- [ ] Tested in desktop / non-VR mode
- [ ] Tested with phone controls (mobile touch input)
- [x] N/A — change does not touch player/XR/input code

Where applicable, confirm these flows still work after your changes:

- [ ] Hot-switching (desktop ↔ VR mode swap at runtime)
- [ ] Avatar swapping
- [ ] Server swapping (joining / leaving / changing servers)
- [x] N/A — change does not touch any of the above

## Notes

This is a native C/C++ plugin change (the MPEG-TS and RTMP demuxers plus
the Windows decoder-config guard) with no Unity C# surface, so the
transform / Addressables / GetComponent / BasisEventDriver /
jobification / property / camera / logging / hot-path required-checks
are all N/A and ticked as such.

**Verification (Windows)** — done with the plugin-loading probe harness,
which loads the shipped `basis_media_native.dll` and drives real
playback, against live feeds:

- Live H.264 RIST feed: previously errored at 0x0, now plays at
1920x1080 with the position advancing.
- HTTP-TS H.264 live: recovers the same way (same mid-GOP join path).
- HEVC-over-TS: still refuses cleanly via the sizeless-track guard, now
with a codec-named message.
- H.264 in MP4: unchanged.

These line up with the mediaplayer `TESTING.md` transport rows (RIST
plain, HTTP-TS live) and the HEVC-in-TS refusal case.

**RTMP** is code-only here — it isn't exercised end-to-end yet, as
there's no public RTMP-pull endpoint stood up to drive it. The change is
the direct analogue of the TS fix (wait for the header carrying the SPS)
and leaves the RTSP and MP4 paths untouched.

**Android** — the arm64 `.so` is rebuilt with the shared demuxer fix but
has not been run on-device; the Windows x64 DLL is the binary verified
above.

Author: dooly123

Basis/Packages/com.basis.mediaplayer/Native~/protocol/basis_rtmp.c

@@ -199,7 +199,11 @@ static void handle_video(rtmp_t* r, basis_media_sink_t* sink, chunk_state_t* c)
             r->video_announced = 1;
         }
     } else if (avc_pkt == 1) { /* NALUs (avcc) -> annex B */
-        if (!r->video_announced) sink->on_video_format(sink->user, r->video_codec, NULL, 0, 0, 0), r->video_announced = 1;
+        /* Media before the avcC sequence header (mid-stream join): its SPS — and
+         * the frame size — only travel in the header, and nothing here decodes
+         * without it. Drop and wait for the header rather than announcing 0x0 and
+         * latching. */
+        if (!r->video_announced) return;
         int nls = r->video_nls ? r->video_nls : 4;
         int cap = basis_avcc_annexb_cap(dlen, nls);
         uint8_t* out = (uint8_t*)malloc((size_t)cap);

Basis/Packages/com.basis.mediaplayer/Native~/protocol/basis_ts.c

@@ -99,10 +99,17 @@ static void flush_video(ts_t* t) {
     if (!t->video_announced) {
         int w = 0, h = 0;
         if (t->video_codec == BASIS_CODEC_H264) {
-            int pos = 0, no, nl;
+            int pos = 0, no, nl, have_sps = 0;
             while ((pos = basis_annexb_next(au, au_len, pos, &no, &nl)) >= 0) {
-                if (nl > 0 && basis_h264_nal_type(au[no]) == 7) { basis_h264_sps_dimensions(au + no, nl, &w, &h); break; }
+                if (nl > 0 && basis_h264_nal_type(au[no]) == 7) {
+                    basis_h264_sps_dimensions(au + no, nl, &w, &h);
+                    if (w > 0 && h > 0) { have_sps = 1; break; }
+                }
             }
+            /* Mid-GOP join (or an SPS we couldn't read dimensions from): drop this
+             * AU — it can't decode without its IDR anyway — and wait for the next
+             * SPS-bearing keyframe instead of announcing 0x0 and latching. */
+            if (!have_sps) { e->len = 0; e->started = 0; return; }
         }
         t->sink->on_video_format(t->sink->user, t->video_codec, NULL, 0, w, h);
         t->video_announced = 1;

Basis/Packages/com.basis.mediaplayer/Native~/windows/basis_win_decode.cpp

@@ -568,9 +568,16 @@ static bool configure_video_mft(basis_decoder* d) {
      * Refuse here: only H.265 elementary streams reach this point sizeless (no SPS
      * parser for TS/RTSP/RTMP), and the size can't be recovered once it crashes. */
     if (d->vwidth <= 0 || d->vheight <= 0) {
-        basis_engine_set_error(d->engine,
-            "video track announced no frame size, so the decoder cannot be configured "
-            "(H.265 outside MP4 has no dimension parser yet)");
+        const char* codec_name =
+            d->vcodec == BASIS_CODEC_H265 ? "H.265" :
+            d->vcodec == BASIS_CODEC_H264 ? "H.264" :
+            d->vcodec == BASIS_CODEC_VP9  ? "VP9"   :
+            d->vcodec == BASIS_CODEC_AV1  ? "AV1"   : "this video codec";
+        char msg[176];
+        snprintf(msg, sizeof(msg),
+            "video track (%s) announced no frame size, so the decoder cannot be configured",
+            codec_name);
+        basis_engine_set_error(d->engine, msg);
         SAFE_RELEASE(d->vdec);
         return false;
     }