adds proper dynamic linking

[lattice0]

dynamic linking was trying to link to a single file

this adds dynamic linking to the various .so files

tested and worked

[lattice0]

I also added multi architecture build. Sometimes when you want to build an Android APK you need a way of passing a single directory with .so files for every architecture.

Now with

FFMPEG_MULTI_ARCH_BUILD=1

FFMPEG_LIBS_DIR will be used as a base, and it will do like this

FFMPEG_LIBS_DIR/{target_os}/target_arch/

and it will search for the libs in this folder.

[lattice0]

would be nice to have this merged :)

[niuhuan]

How to build for android and iOS ?

I had bulit ffmpeg-kit ,

and add this to cargo.toml
rusty_ffmpeg = { git = "https://github.com/lattice0/rusty_ffmpeg.git", branch = "master" }

then run cargo ndk build
FFMPEG_PKG_CONFIG_PATH=/Volumes/DATA/Projects/ffmpeg-kit/prebuilt/android-arm64/ffmpeg/lib/pkgconfig cargo ndk -t arm64-v8a build

error: failed to run custom build command for `rusty_ffmpeg v0.10.0+ffmpeg.5.1`

Caused by:
  process didn't exit successfully: `/Volumes/DATA/Projects/bili-cli-rs/target/debug/build/rusty_ffmpeg-e44e608450ec302b/build-script-build` (exit status: 101)

  --- stderr
  thread 'main' panicked at 'avcodec not found!', /Volumes/DATA/Runtimes/.cargo/registry/src/github.com-1ecc6299db9ec823/rusty_ffmpeg-0.10.0+ffmpeg.5.1/build.rs:247:37
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

✗ ls /Volumes/DATA/Projects/ffmpeg-kit/prebuilt/android-arm64/ffmpeg/lib/
libavcodec.so    libavfilter.so   libavutil.so     libswscale.so
libavdevice.so   libavformat.so   libswresample.so pkgconfig

[emilazy]

It would be great to be able to properly dynamically link on Unix platforms. If me rebasing this PR would make any difference to getting it merged let me know.

[SimonRacaud]

Missing rustc-link-search ?
++ println!("cargo:rustc-link-search=native={}", ffmpeg_dll_path);

[SimonRacaud]

I needed to link ffmpeg dlls directly to the project (my dev PC must be offline -> military project), and I can confirm that in single architecture build mode, it works (with a little alteration).
For those in the same situation than me, I used the following env vars to make it works:

# (In config.toml)

[env]
# To generate the binding:
FFMPEG_INCLUDE_DIR = { value = '..\dependencies\win\ffmpeg_msvc\include', relative = true, force = true }
# To indicate location of avcodec, avutil, swresample, (..) => `.dll` AND `.lib`
FFMPEG_DLL_PATH = { value = '..\dependencies\win\ffmpeg_msvc\bin\', relative = true, force = true }