Building gst-plugins-good/ext/jpeg

[Ryan Melville]

> I have not added a new lib myself. Please take a look how faad is integrated and try to follow that. If you success,
> it would be great if you could contribute the solution. On the other hand I wonder if you could get away with adding
> the libjpeg-devel related files (headers and pkg-config files) and copy the libjpeg library from the phone to the ndk
> like we do for other media libs.
>
> Stefan

Thank you for the tips, Stefan.  It got me going in the right direction.

I believe I've been successful; here are my notes for posterity...

* Problem

I needed libgstjpeg.so from gst-plugins-good/ext/jpeg but it wasn't building by default in the gstreamer-0.10_ndk_build package by default.

* My Solution

First, I noticed that my build output showed:

     configure: *** checking feature: jpeg library ***
     configure: *** for plug-ins: jpeg ***
     checking for jpeg_set_defaults in -ljpeg-mmx... no
     checking for jpeg_set_defaults in -ljpeg... no
     configure: *** These plugins will not be built: jpeg

libgstjpeg is dependent upon libjpeg, which doesn't seem to be in the Android NDK nor gstreamer-0.10_ndk_build package.  It seems to be in the Android OS source tree (ICS; system/external/jpeg) and so I would expect the library to be on ICS devices at run-time, but I need it and the headers at compile/link time, of course.  And I don't want to have to have the entire Android OS source tree around every time I build my project...

So I created my own my_stuff/android/android-14/system/external/jpeg directory containing *.h from the original, a prebuilt lib/armeabi/libjpeg.so (prebuilt via building the entire Android OS source tree) and I adjusted the Android.mk.  One could probably pull libjpeg.so from an existing device as well to avoid having to build the entire Android OS source tree.

I basically added this near the top of the existing jpeg/Android.mk (after the standard LOCAL_PATH and CLEAR_VARS lines); most of this came from the Android NDK docs on "Prebuilt" libraries:

     ifneq ($(SYSROOT),)
     NDK_BUILD := true
     else
     NDK_BUILD := false
     endif

     ifeq ($(NDK_BUILD),true)

     LOCAL_MODULE := libjpeg
     LOCAL_SRC_FILES := lib/$(TARGET_ARCH_ABI)/libjpeg.so
     LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)
     include $(PREBUILT_SHARED_LIBRARY)

     else

      [...rest of original file...]

     endif

Then, I enabled the ext/jpeg plugin in gst-plugins-good/Android.mk by adding "ext/jpeg/Android.mk" to the end of the GST_PLUGINS_GOOD_BUILT_SOURCES list and "-include $(GST_PLUGINS_GOOD_TOP)/ext/jpeg/Android.mk" to the list of included Android.mk files near the bottom.

I also add to add a rule to make ext/jpeg/Android.mk at the end of the gst-plugins-good/ext/jpeg/Makefile.am file.  I copied this from a different plugin that was building correctly after getting a "No rule to make target Android.mk" build error:

     Android.mk: Makefile.am $(BUILT_SOURCES)
      androgenizer \
      -:PROJECT libgstjpeg -:SHARED libgstjpeg \
       -:TAGS eng debug \
       -:REL_TOP $(top_srcdir) -:ABS_TOP $(abs_top_srcdir) \
       -:SOURCES $(libgstjpeg_la_SOURCES) \
       -:CFLAGS $(DEFS) $(DEFAULT_INCLUDES) $(libgstjpeg_la_CFLAGS) \
       -:LDFLAGS $(libgstjpeg_la_LDFLAGS) \
                 $(libgstjpeg_la_LIBADD) \
                 -ldl \
       -:PASSTHROUGH LOCAL_ARM_MODE:=arm \
                     LOCAL_MODULE_PATH:='$$(TARGET_OUT)/lib/gstreamer-0.10' \
      > $@

Lastly, I had to add inclusion of the libjpeg Android.mk file to my project's Android.mk file (equivalent of gstreamer-0.10_ndk_build/jni/Android.mk):

     #include $(JPEG_TOP)/Android.mk

Where "JPEG_TOP" was set to my previously mentioned "my_stuff/android/android-14/system/external/jpeg" directory.

Now, libjpeg is detected and libgstjpeg.so is built.

Regards,

Ryan