[MattiaSt1]

What

Adds full ASS/SSA subtitle rendering through libass 0.17.5, built from source.

How

• LibassSubtitleSupport bridges ExoPlayer and libass. It gets the playback
  position from a NoSampleRenderer, renders on a dedicated thread and draws the
  result in a transparent overlay view inside exo_content_frame, so it follows
  resize modes and pinch zoom.
• External files (URL, downloaded, OpenSubtitles): CustomDecoder loads the
  whole file into libass and stops forwarding text cues. SsaParser still runs,
  so subtitle sync keeps working.
• MKV: UpdatedMatroskaExtractor sends each dialogue and the attached fonts to
  libass; the wrapped subtitle parser factory returns a no-op parser for those
  tracks.
• Subtitle offset is applied to libass as well.
• New setting "ASS/SSA rendering" in Settings > Player > Subtitles
• Other subtitle formats are unchanged. If libass fails to load, the normal
  subtitle pipeline is used.

Native build

• app/src/main/cpp/libass-deps.cmake downloads the official release tarballs of libass 0.17.5,
  FreeType 2.15.0, FriBidi 1.0.17 and HarfBuzz 14.6.0. Each tarball is checked against a pinned
  SHA-256 and the build fails on any mismatch. Nothing prebuilt is downloaded. The libass and
  FreeType hashes come from tarballs with a verified PGP signature (FriBidi and HarfBuzz do not
  sign their releases).
• The sources (~25 MB) are downloaded once into app/build/libass-deps and shared between ABIs
  and variants. No CI changes are needed, Gradle installs the NDK if missing.
• CMakeLists.txt builds everything as static libraries: FreeType without external
  dependencies, FriBidi with its config headers written by CMake (it only has a meson build),
  HarfBuzz as a single file without optional integrations, and libass with its ARM64 assembly
  on arm64 (the x86 assembly needs NASM, so the C version is used there).
• Everything is linked into libcs3ass.so together with the static C++ runtime, so it can not
  clash with the other native libraries. It only exports the JNI functions, only depends on
  system libraries and is 16 KB page aligned. About 1.5–2.2 MB per ABI.
• No new Gradle dependencies.
• Updating a dependency means changing its version and hash in libass-deps.cmake.

Testing

Attached libass_effects_test.ass: 16 scenes covering positioning, colors,
fades, movement, 3D rotations, karaoke, clips, vector drawings, transparency
and non-Latin scripts. Load it on any video.

Tested on: Pixel 11 Pro XL

AI USED (Claude opus 5.5)
libass_effects_test.ass.txt

[fire-light42]

Nice!

I am planning on making this a dependency within the recloudstream organization, with your code as the basis. Is that okay? I want to remove the C++ build process entirely within CloudStream.

Your pull request will still remain, the build will just be substituted with an implementation(...)

[MattiaSt1]

Feel free to do whatever you think is best.