Techniques and tools for quality control in frame interpolation and motion analysis are described. The techniques and tools may be implemented separately or in combination in software and/or hardware devices for various applications. For example, a media playback device uses quality control in frame interpolation with motion analysis to increase the frame rate of streamed video for playback. The device selectively uses frame synthesis to increase frame rate and quality under normal circumstances, but avoids using frame synthesis when it would not provide suitable quality improvement. The device uses selective ghosting reduction and selective feathering to reduce artifacts in synthesized frames.