Friday, November 25, 2016


This is some quick notes on cross compiling xawtv. I had to get a webcam working on an embedded device this week and after not getting much success with a simple v4l app, (derived from simplewebcam android app's native library), I decided to cross compile xawtv. The only interesting part was the streamer console application.

I cross compiled this for arm. There was not much support for cross compilation as far as I could see.

XawTv depended on libv4l for which I had to compile v4l utils. This in turn needed libjpeg support. SourceForge gave me version 6 of libjpeg which had issues with libtool while cross compiling. Eventually I built version 9 which was obtained from some other location. To get the library, i had to use --enable-shared flag at the time of configuring. Then I compiled v4l utils. All this was done by setting LDFLAGS, CFLAGS and CXXFLAGS appropriately. As I remember, compiling v4l utils needed -Wl,-rpath-link=path_to_jpeglib in compiled flags.

There was some code that needed x11 libraries and I just commented them using # if 0. Another point to note is that output goes to .lib for these packages.

Now, for xawtv, I set the compiler and linker flags and configured using --host option to indicate that it is a cross compilation. However, I ran into problems as LDFLAGS was not honoured. After a long struggle, I figured out that flag was called DLFLAGS or something similar in Makefile. I set that to my current LDFLAGS value. Things went fine to some extend and I got streamer compiled. However, I was getting many warnings and errors since the build kept looking at /usr/include though I was cross compiling. Using -nostdinc only worsened the pain as I had to then use -I flag for each standard include folder and sub folders. So, I gave up on that and looked at what was causing the error. I could see that among many warnings there was only one error. It was related to FD_XXX macros of select.

Though I first ignored all these and decided to use only streamer (which was already compiled at this stage), my happiness was short lives as I found that the streamer used libng and the plugins present inside that folder.

I then commented many places where select appeared. However, same was appearing in v4l drivers. There alone I replaced select with Poll. My streamer and drivers were now ready. But, while running, streamer was not able to load drivers due to some unresolved symbols in drivers.

After a feel in entire source code, I found that they were present in libng and I only had a static library for libng. At this point, a word about makefiles in xawtv. The top folder has main Makefile. It then had in each sub-folder which is included by main make file. Quick look at Will give one a good idea about how to build an application/library. After seeing the objects that go into libng.a, I wrote a simple make file to get a corresponding .so file (arm-xxx-gcc -fPIC -shared needed.o -o Then I wrote a similar make file for streamer and used this so to build streamer. (Streamer was using .a earlier). Then I copied the streamer and new to target.

Viola! "./streamer -o image.ppm -D v4l2" gave me my first image and I ended my day's work after seeing it via ppm2tiff. Well, I was really refreshing to see the same old mundane scenes via that image :)

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