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Render ASS/SSA subtitles with libass #3260

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d3e3081
Add full ASS/SSA subtitle rendering with libass
MattiaSt1 Oct 20, 2026
b8dd5fb
fix codefactor
MattiaSt1 Oct 20, 2026
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17 changes: 17 additions & 0 deletions app/build.gradle.kts
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Original file line number Diff line number Diff line change
Expand Up @@ -140,6 +140,23 @@ android {
"\"" + (System.getenv("ANILIST_KEY") ?: localProperties["anilist.key"]) + "\""
)
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"

externalNativeBuild {
cmake {
// Static C++ runtime so it can not clash with the other native libraries
arguments += "-DANDROID_STL=c++_static"
// Shared between ABIs and variants so the sources are only downloaded once
arguments += "-DLIBASS_DEPS_DIR=${layout.buildDirectory.get().asFile.invariantSeparatorsPath}/libass-deps"
}
}
}

// libass for ASS/SSA subtitles
externalNativeBuild {
cmake {
path = file("src/main/cpp/CMakeLists.txt")
version = "3.22.1"
}
}

buildTypes {
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154 changes: 154 additions & 0 deletions app/src/main/cpp/CMakeLists.txt
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cmake_minimum_required(VERSION 3.22.1)

# libass (https://github.com/libass/libass) for ASS/SSA subtitles, see LibassSubtitleSupport.kt
#
# libass, FreeType, FriBidi and HarfBuzz are built as static libraries and linked into
# libcs3ass.so. The sources are downloaded by libass-deps.cmake.
# Fontconfig is not used, fonts come from the subtitle (MKV attachments or [Fonts]) or the
# default system font.
project(cs3ass C CXX ASM)

set(CMAKE_POSITION_INDEPENDENT_CODE ON)
set(CMAKE_C_VISIBILITY_PRESET hidden)
set(CMAKE_CXX_VISIBILITY_PRESET hidden)
set(CMAKE_VISIBILITY_INLINES_HIDDEN ON)

# Subtitles are rendered every frame, so optimize debug builds too
add_compile_options(-O2 -ffunction-sections -fdata-sections)

include(libass-deps.cmake)

set(GENERATED_DIR "${CMAKE_CURRENT_BINARY_DIR}/generated")

# FreeType
set(FT_DISABLE_ZLIB ON CACHE BOOL "" FORCE)
set(FT_DISABLE_BZIP2 ON CACHE BOOL "" FORCE)
set(FT_DISABLE_PNG ON CACHE BOOL "" FORCE)
set(FT_DISABLE_HARFBUZZ ON CACHE BOOL "" FORCE)
set(FT_DISABLE_BROTLI ON CACHE BOOL "" FORCE)
set(BUILD_SHARED_LIBS OFF CACHE BOOL "" FORCE)
add_subdirectory("${FREETYPE_SOURCE_DIR}" freetype EXCLUDE_FROM_ALL)

# FriBidi only has a meson build, so its config headers are written here.
# The release tarball already contains the generated Unicode tables (*.tab.i).
set(FRIBIDI_GENERATED_DIR "${GENERATED_DIR}/fribidi")
file(WRITE "${FRIBIDI_GENERATED_DIR}/config.h"
"#define HAVE_MEMMOVE 1\n"
"#define HAVE_MEMSET 1\n"
"#define HAVE_STRDUP 1\n"
"#define HAVE_STDLIB_H 1\n"
"#define HAVE_STRING_H 1\n"
"#define HAVE_MEMORY_H 0\n"
"#define HAVE_STRINGS_H 1\n"
"#define HAVE_SYS_TIMES_H 1\n"
"#define STDC_HEADERS 1\n"
"#define HAVE_STRINGIZE 1\n"
)
string(REPLACE "." ";" FRIBIDI_VERSION_PARTS "${FRIBIDI_VERSION}")
list(GET FRIBIDI_VERSION_PARTS 0 FRIBIDI_MAJOR_VERSION)
list(GET FRIBIDI_VERSION_PARTS 1 FRIBIDI_MINOR_VERSION)
list(GET FRIBIDI_VERSION_PARTS 2 FRIBIDI_MICRO_VERSION)
set(configure_input "fribidi-config.h generated by CMake")
set(PACKAGE fribidi)
set(PACKAGE_NAME "GNU FriBidi")
set(PACKAGE_BUGREPORT "https://github.com/fribidi/fribidi/issues/new")
set(FRIBIDI_INTERFACE_VERSION 4)
set(SIZEOF_INT 4)
set(FRIBIDI_MSVC_BUILD_PLACEHOLDER "#undef FRIBIDI_BUILT_WITH_MSVC")
configure_file("${FRIBIDI_SOURCE_DIR}/lib/fribidi-config.h.in"
"${FRIBIDI_GENERATED_DIR}/fribidi-config.h" @ONLY)

add_library(fribidi STATIC
"${FRIBIDI_SOURCE_DIR}/lib/fribidi.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-arabic.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-bidi.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-bidi-types.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets-cap-rtl.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets-cp1255.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets-cp1256.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets-iso8859-6.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets-iso8859-8.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-char-sets-utf8.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-deprecated.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-joining.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-joining-types.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-mirroring.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-brackets.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-run.c"
"${FRIBIDI_SOURCE_DIR}/lib/fribidi-shape.c"
)
target_include_directories(fribidi PUBLIC "${FRIBIDI_GENERATED_DIR}" "${FRIBIDI_SOURCE_DIR}/lib")
target_compile_definitions(fribidi PRIVATE HAVE_CONFIG_H)

# HarfBuzz, single file build without any of the optional integrations
add_library(harfbuzz STATIC "${HARFBUZZ_SOURCE_DIR}/src/harfbuzz.cc")
target_include_directories(harfbuzz PUBLIC "${HARFBUZZ_SOURCE_DIR}/src")
target_compile_features(harfbuzz PRIVATE cxx_std_11)
target_compile_options(harfbuzz PRIVATE -fno-exceptions -fno-rtti -fno-threadsafe-statics)

# libass
set(LIBASS_GENERATED_DIR "${GENERATED_DIR}/libass")
set(LIBASS_CONFIG
"#define HAVE_STRDUP 1\n"
"#define HAVE_STRNDUP 1\n"
"#define CONFIG_LARGE_TILES 0\n"
"#define CONFIG_SOURCEVERSION \"cloudstream, release ${LIBASS_VERSION}\"\n"
)
set(LIBASS_SOURCES
"${LIBASS_SOURCE_DIR}/libass/c/c_be_blur.c"
"${LIBASS_SOURCE_DIR}/libass/c/c_blend_bitmaps.c"
"${LIBASS_SOURCE_DIR}/libass/c/c_blur.c"
"${LIBASS_SOURCE_DIR}/libass/c/c_rasterizer.c"
"${LIBASS_SOURCE_DIR}/libass/ass.c"
"${LIBASS_SOURCE_DIR}/libass/ass_arabic_charmap.c"
"${LIBASS_SOURCE_DIR}/libass/ass_bitmap.c"
"${LIBASS_SOURCE_DIR}/libass/ass_bitmap_engine.c"
"${LIBASS_SOURCE_DIR}/libass/ass_blur.c"
"${LIBASS_SOURCE_DIR}/libass/ass_cache.c"
"${LIBASS_SOURCE_DIR}/libass/ass_drawing.c"
"${LIBASS_SOURCE_DIR}/libass/ass_filesystem.c"
"${LIBASS_SOURCE_DIR}/libass/ass_font.c"
"${LIBASS_SOURCE_DIR}/libass/ass_fontselect.c"
"${LIBASS_SOURCE_DIR}/libass/ass_library.c"
"${LIBASS_SOURCE_DIR}/libass/ass_outline.c"
"${LIBASS_SOURCE_DIR}/libass/ass_parse.c"
"${LIBASS_SOURCE_DIR}/libass/ass_rasterizer.c"
"${LIBASS_SOURCE_DIR}/libass/ass_render.c"
"${LIBASS_SOURCE_DIR}/libass/ass_render_api.c"
"${LIBASS_SOURCE_DIR}/libass/ass_shaper.c"
"${LIBASS_SOURCE_DIR}/libass/ass_string.c"
"${LIBASS_SOURCE_DIR}/libass/ass_strtod.c"
"${LIBASS_SOURCE_DIR}/libass/ass_utils.c"
)
# Only the ARM64 assembly is used, the x86 one needs NASM
if(ANDROID_ABI STREQUAL "arm64-v8a")
string(APPEND LIBASS_CONFIG "#define CONFIG_ASM 1\n#define ARCH_AARCH64 1\n")
list(APPEND LIBASS_SOURCES
"${LIBASS_SOURCE_DIR}/libass/aarch64/asm.S"
"${LIBASS_SOURCE_DIR}/libass/aarch64/be_blur.S"
"${LIBASS_SOURCE_DIR}/libass/aarch64/blend_bitmaps.S"
"${LIBASS_SOURCE_DIR}/libass/aarch64/blur.S"
"${LIBASS_SOURCE_DIR}/libass/aarch64/rasterizer.S"
)
endif()
file(WRITE "${LIBASS_GENERATED_DIR}/config.h" ${LIBASS_CONFIG})

add_library(ass STATIC ${LIBASS_SOURCES})
target_include_directories(ass
PRIVATE "${LIBASS_GENERATED_DIR}"
PUBLIC "${LIBASS_SOURCE_DIR}/libass"
)
target_compile_definitions(ass PRIVATE _GNU_SOURCE _XPLATFORM_SOURCE)
target_compile_options(ass PRIVATE $<$<COMPILE_LANGUAGE:C>:-std=gnu99 -fno-math-errno>)
target_link_libraries(ass PRIVATE freetype fribidi harfbuzz m)

# JNI bindings
add_library(cs3ass SHARED libass_jni.c)
target_link_libraries(cs3ass PRIVATE ass freetype fribidi harfbuzz jnigraphics log m)
target_link_options(cs3ass PRIVATE
-Wl,--gc-sections
-Wl,--exclude-libs,ALL
# 16 KB page size support
-Wl,-z,max-page-size=16384
)
77 changes: 77 additions & 0 deletions app/src/main/cpp/libass-deps.cmake
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# Source tarballs of libass and its dependencies, all from the official releases.
# Every tarball is checked against its SHA-256, nothing prebuilt is downloaded.
#
# The libass and FreeType hashes come from tarballs with a valid PGP signature:
# libass Oneric DDAFC19E46B2AD2D6B26F84397A08E0CFFD70951
# FreeType Werner Lemberg E30674707856409FF1948010BE6C3AAC63AD8E3F
# FriBidi and HarfBuzz do not sign their releases.
#
# When updating a dependency change the version and the hash together.

set(LIBASS_DEPS_DIR "${CMAKE_BINARY_DIR}/libass-deps" CACHE PATH
"Where the dependency sources are downloaded")

set(LIBASS_VERSION 0.17.5)
set(LIBASS_URL "https://github.com/libass/libass/releases/download/${LIBASS_VERSION}/libass-${LIBASS_VERSION}.tar.xz")
set(LIBASS_SHA256 2dca25c0e0c837ddf00b52011b3f82cac1e4ddd3ad018227806b0c2288864acc)

set(FREETYPE_VERSION 2.15.0)
set(FREETYPE_URL "https://download.savannah.gnu.org/releases/freetype/freetype-${FREETYPE_VERSION}.tar.xz")
set(FREETYPE_SHA256 93cd47eb719c325107f2d3cf087d06299e944c3b48a40b55537302304dea1dd5)

set(FRIBIDI_VERSION 1.0.17)
set(FRIBIDI_URL "https://github.com/fribidi/fribidi/releases/download/v${FRIBIDI_VERSION}/fribidi-${FRIBIDI_VERSION}.tar.xz")
set(FRIBIDI_SHA256 6949dcde27d41cebad1fd741fcafc36d55a1020d2d872d4a6eb3914caabbada2)

set(HARFBUZZ_VERSION 14.6.0)
set(HARFBUZZ_URL "https://github.com/harfbuzz/harfbuzz/releases/download/${HARFBUZZ_VERSION}/harfbuzz-${HARFBUZZ_VERSION}.tar.xz")
set(HARFBUZZ_SHA256 d07a007327277708a2a73ae437887cdbaf282937f6d03ca5467723e9099af586)

# Downloads and extracts a tarball if needed, sets <name>_SOURCE_DIR
function(libass_fetch_source name url sha256 top_dir)
get_filename_component(archive_name "${url}" NAME)
set(archive "${LIBASS_DEPS_DIR}/${archive_name}")
set(extract_dir "${LIBASS_DEPS_DIR}/${name}")
set(stamp "${extract_dir}/.sha256-${sha256}")

if(NOT EXISTS "${stamp}")
set(have_archive FALSE)
if(EXISTS "${archive}")
file(SHA256 "${archive}" existing_hash)
if(existing_hash STREQUAL sha256)
set(have_archive TRUE)
endif()
endif()

if(NOT have_archive)
message(STATUS "Downloading ${url}")
file(DOWNLOAD "${url}" "${archive}"
EXPECTED_HASH SHA256=${sha256}
TLS_VERIFY ON
STATUS download_status)
list(GET download_status 0 download_code)
if(NOT download_code EQUAL 0)
list(GET download_status 1 download_error)
file(REMOVE "${archive}")
message(FATAL_ERROR "Could not download ${url}: ${download_error}")
endif()
endif()

file(REMOVE_RECURSE "${extract_dir}")
file(ARCHIVE_EXTRACT INPUT "${archive}" DESTINATION "${extract_dir}")
file(TOUCH "${stamp}")
endif()

set(${name}_SOURCE_DIR "${extract_dir}/${top_dir}" PARENT_SCOPE)
endfunction()

# All ABIs are configured in parallel, only download once
file(MAKE_DIRECTORY "${LIBASS_DEPS_DIR}")
file(LOCK "${LIBASS_DEPS_DIR}/.lock" GUARD FILE TIMEOUT 900)

libass_fetch_source(LIBASS "${LIBASS_URL}" ${LIBASS_SHA256} "libass-${LIBASS_VERSION}")
libass_fetch_source(FREETYPE "${FREETYPE_URL}" ${FREETYPE_SHA256} "freetype-${FREETYPE_VERSION}")
libass_fetch_source(FRIBIDI "${FRIBIDI_URL}" ${FRIBIDI_SHA256} "fribidi-${FRIBIDI_VERSION}")
libass_fetch_source(HARFBUZZ "${HARFBUZZ_URL}" ${HARFBUZZ_SHA256} "harfbuzz-${HARFBUZZ_VERSION}")

file(LOCK "${LIBASS_DEPS_DIR}/.lock" RELEASE)
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