Is it possible to use media sdk (NDK) introduced in lollipop into a project to run on Android 16 +

Question

I am trying to build a project using NDK media sdk, but I need it to run on older phones too (to support 90% of the market...). Now, I am able to include the libmediasdk.so & libOpenMAXAL.so manually, and it seem to link properly, but I am not sure this is a correct practice. Moreover, the libraries (libmediasdk.so & libOpenMAXAL.so) are expected to be available on the target device, so unless I do copy them manually to the project/libs/arch-arm the application complains libraries are not found.

Have I gone too far ? :) hope not..

Answer 1

You can write code that optionally uses the new native media functions (libmediandk.so), but you can only use it on Android 21+. So if you want to support older android versions, you must make this codepath optional, allowing it to fail cleanly on other devices where libmediandk.so doesn't exist.

If the MediaCodec APIs are optional within your app and you are ok with them only being available on Android 21+, you can just make sure you build this into a separate lib (like libyourapp-media.so), and be ready to handle the case when System.loadLibrary() for this library fails.

However, if you want to use other native code components in your app, there's a few gotchas you need to know. If you build your app targeting android-21 and your native code uses certain functions (such as atof), it will only run on android-21 or newer (even if code using the function atof would build just fine for the older platforms). The reason for this is that the atof function didn't exist before, and calls to it were redirected to strtod. If you build your library targeting android-21, it will actually do the calls to atof instead, which doesn't exist in the older platform versions. This also goes for quite a number of other functions, not only atof. See http://b.android.com/73725 for details on this.

Therefore, if you want to use the new native media APIs in a library that should be loadable on older versions (except for the native media APIs that obviously won't work on older versions), you need to build your native components targeting an older android version. You'd need to duplicate the media/* headers from android-21, but instead of linking to libmediandk.so (-lmediandk in LOCAL_LDLIBS), you'd need to load this library at runtime using dlopen.

If you need to do the same on older platforms as well, you should use the MediaCodec API in java (which you can call via JNI). Then, there's little point in doing all of this extra work just to use the native version of the API on Android 21+, when you can use the java API on all versions (it works from Android 16, and more reliably since Android 18).