In version 0.5.2, I can't get video to work. If I open SubtitleComposer, the place where video should be is kinda transparent, it shows my desktop! If I open a movie, there's only sound, video window desn't change. Tryied it with all video backends available.
Video playback was broken with Qt 4.5. The issue was fixed in Subtitle Composer v0.5.3.
i can confirm that with qt 4.7 and subtitle composer version 0.5.3. i'm using kde 4.5.5.