Don't report framerate in y4m for unknown fps clips
Don't report framerate in y4m for unknown fps clips

Kamekameha/vapoursynth,vapoursynth/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth,Kamekameha/vapoursynth,vapoursynth/vapoursynth,Kamekameha/vapoursynth,vapoursynth/vapoursynth