Build scripts of the libraries try to enable all CPU optimizations possible. But some libraries do not support CPU optimizations and configure/build operations fail when asm is enabled.

Below you can see the libraries and architectures that do not support asm. Other than these, all libraries are built with asm enabled.

• gmp: Enabling assembly produces cannot locate symbol "__gmp_binvert_limb_table" error when library is loaded.
• gnutls, libass, xvidcore, x264: Enabling asm for x86 ABI causes text relocation errors in libavfilter.so, libavformat.so and libavcodec.so.
• libass: Library does not support ASM on arm CPUs.
• libtheora: asm is disabled on LTS releases. Enabling asm causes random crashes on pre API 21 devices.
• libwebp: This library dropped support for arm-v7a architecture (armeabi-v7a without NEON) with release 1.0.2. Therefore, asm is disabled for arm-v7a architecture.
• openh264 is built without -DHAVE_NEON flag on arm-v7a-neon architecture. -DHAVE_NEON flag causes undefined symbol errors for WelsCopy8x8_neon.
• x265: Assembly compilation fails for arm64-v8a architecture. It is possible to build arm-v7a, arm-v7a-neon and x86 with assembly enabled but all three ABIs include relocation errors. Additionally, assembly on x86-64 causes linking errors.

• gmp: Enabling assembly on armv7, armv7s, arm64 and arm64e architectures causes configure to fail with configure: error: cannot determine how to define a 32-bit word.

• kvazaar, libaom, libass, libvpx, openh264: Enabling asm in x86-64 architecture does not cause any compilation errors. But creating xcframework bundles fails with the following error. Assembly is disabled for these libraries in x86-64 architecture to resolve this error.

  The CodingKeys(stringValue: "SupportedPlatform", intValue: nil) is empty in library -x86_64.

• libass: Library does not support ASM on arm CPUs.

• libjpeg-turbo: Build fails on i386 architecture with error: symbol '.no_avx2' undefined error.

• wavpack: Build fails on all arm architectures when asm is enabled.

• xvidcore: Build fails for i386 architecture when asm is enabled. ffmpeg crashes when asm is enabled on x86-64 architecture.

• x265: Assembly compilation fails for arm64 and arm64e architectures.