Ffmpeg rawvideo conversion error

Screencapture command:
ffmpeg -r 25 -f x11grab -s 1280x720 -i :0.0+1024,0 -f rawvideo out.yuv

Convert to h264 file:
ffmpeg -i out.yuv -c:v libx264 -crf 16 -preset fast test.mp4

gives error:
..
[IMGUTILS @ 0x7fff8b4c2350] Picture size 0x0 is invalid
[IMGUTILS @ 0x7fff8b4c2180] Picture size 0x0 is invalid
[rawvideo @ 0x62e0e0] Could not find codec parameters (Video: rawvideo, yuv420p)
[rawvideo @ 0x62e0e0] Estimating duration from bitrate, this may be inaccurate
out.yuv: could not find codec parameters