The spike proved compositing works on Linux, including Wayland, and left two
blockers. One is now closed: DR-228 measured a single EXT-X-STREAM-INF in the
server's master playlist, so there is no adaptive bitrate for mpv to lose and
finding 3 of playback-backend-unification.md is false. The spike is updated to
record that. The other — an unexplained SIGSEGV in a decoder thread — is carried
into the spec as DR-231 rather than chased: the spike had no render-context
teardown at all, which is DR-184 on Android restated, and removing the likeliest
cause is worth doing whether or not it was the cause.
The spec targets every desktop platform rather than Linux alone, because the
maintenance argument runs the other way. Video has three renderers today. A
Linux-only version makes it four, permanently — mpv on Linux, HTML5 on Windows,
ExoPlayer on Android, hls.js underneath — and the webview path then survives
indefinitely because something still needs it. Finishing the job leaves mpv on
desktop and ExoPlayer on Android, and hls.js, html5Adapter.ts, videoLoaderFor
and the <video> element are deleted in a phase that has its own acceptance
criterion so it cannot quietly become "later".
The load-bearing change is DR-233: the device profile stops being a
compile-time platform constant and becomes a property of the renderer that will
decode the stream. The measured 7% desktop direct-play rate and Android's 85%
differ by nothing except which component decodes, so that one change is what
converts the former toward the latter. It looks like configuration and is not —
it decides whether the server re-encodes, and it fails silently when wrong.
Windows is costed rather than waved at: the surface is genuinely different code
(WebView2 in an HWND, not GTK), but everything else is shared, so nothing may be
guarded on cfg!(target_os = "linux"). The real cost is build — libmpv is a
Linux-only dependency while Windows cross-compiles via cargo-xwin, so a Windows
libmpv must reach that build and ship in the NSIS bundle under the LGPL terms
DR-216 already records.
Allocates UR-080, DR-230..236, IR-033. No product code yet.
Three corrections to the Linux native-video spike, each of which reverses
something recorded earlier in the same session:
- The crash is unexplained. It was first blamed on hwdec=auto-safe's Vulkan
failures, on a misreading of the logs — those are two per run at start-up,
not per-frame, and every clean run has the same two. A 300s soak on
auto-safe survived. So did 240s of automated fullscreen toggling (~120
transitions) and 240s of continuous resizing (~2000 reallocations). Three
hypotheses, none reproduced. Recorded rather than dismissed: an
intermittent fault nobody can reproduce is worse to inherit than a
deterministic one.
- G5 drops to amber. It looked and felt smooth, but the only SIGSEGV observed
came from the only session in which fullscreen was exercised, and the spike
has no lifecycle handling at all — it never frees the render context. An
implementation must bind that to the GL context's lifetime regardless of
what caused this crash, because Android already paid for that lesson as
DR-184.
- Finding 3's premise is in doubt. "The webview path already has real ABR via
hls.js" was never checked against the URLs this app builds:
get_video_stream_url requests a single rendition, the frontend has no
level-handling code at all, and a quality switch is implemented by
re-opening the stream. If the playlist is single-variant there is no
adaptation to lose. The decisive test needs a live server and is recorded
as unrun.
Also records hardware decode working through the render API (nvdec-copy
engaged), and that hwdec=vaapi silently fell back to software on this box.
Adds the spike write-up and re-opens finding 2 of
playback-backend-unification.md, which concluded that video cannot unify
on a native engine because the webview owns the surface.
That finding's general form has since been falsified on Android, where
native video composites behind a transparent WebView and ships on by
default. The evidence behind it was also entirely about foreign-window
embedding -- mpv's render API, drawing into a GL context we own inside
Tauri's own GTK tree, was never tested. The spike tests that one claim
and comes back green on Linux for both X11 and Wayland, bar the Tauri
default_vbox() half of G1.
Findings 3-6 are deliberately left standing. Finding 3 in particular --
mpv has no adaptive bitrate -- is an independent disqualifier that a
green compositing result does not clear, and the spike says so rather
than reading as a green light.
The next-free-id line moves to UR-079 / IR-033 / DR-219: this branch
allocated UR-077 and UR-078 for the updater and diagnostics work, and
DR-215 through DR-218 with them, after that line was last written.
Authored in a parallel session working in the same checkout; committed
here so it travels with the rest of the branch.
dtourolle