Release vs profiling vs debug builds of gstreamer for magicleap

[asajeffrey]

At the moment we're just using the defaultdebugoptimized build of gstreamer for all magicleap builds. Should we use release by default, and reserve debugoptimized for profiling, and use debug for debug builds?

[asajeffrey]

IRC chat with @xclaesse: https://mozilla.logbot.info/servo-magicleap/20190916#c16619838

[nirbheek]

Using debug without optimizations should be avoided with gstreamer because disabling all optimizations tends to make multimedia code very very slow. But sometimes it's unavoidable, of course.

[xclaesse]

IMHO, you should leave the default buildtype (debugoptimized) for debug/developer builds, and use --buildtype release for user builds. If you need unoptimized build for specific debugging, then you can always rebuild yourself with --buildtype debug.

As far as I know the only main difference between debugoptimized and release is glib gets built with -DG_DISABLE_CAST_CHECKS that speed-up all those MyObject *self = MY_OBJECT(gobject);

TIL, GStreamer does not disable cast checks when doing release builds, it has a special option gobject-cast-checks for that, and disable casts by default on even versions numbers. Since Servo uses GStreamer 1.16 branch, it means that cast checks are always disabled. IMHO that's wrong, gst should be changed to follow the same pattern as glib, if only for consistency. I'll open a bug report about that.