QuickTime reporting corrupt file when using H264 encoding

When generating previews using H264 encoding (automated alternatives or just normal previews), sometimes depending on options used to generate the preview, QuickTime can complain that the downloaded mp4 file is corrupt.

YUV planar color space with 4:2:0 chroma subsampling is a safe pixel format for H.264 video to avoid compatibility issues on QuickTime. Use:

-vf format=yuv420p
-pix_fmt yuv420p
to the preview options.