ffmpeg pixel format definitions
If your question was


  Where are these pixel formats defined?


Go to http://ffmpeg.org/download.html and download the source of ffmpeg. Then unpack it

tar -xavf FILENAME.tar.*


and descend to the folder in the source code that is called libavutil

cd ffmpeg-*/libavutil/


and open the file pixfmt.h where you will find a description of all pixel formats. A few sample lines

AV_PIX_FMT_YUV420P,   ///&lt; planar YUV 4:2:0, 12bpp, (1 Cr &amp; Cb sample per 2x2 Y samples)          
AV_PIX_FMT_YUYV422,   ///&lt; packed YUV 4:2:2, 16bpp, Y0 Cb Y1 Cr
AV_PIX_FMT_RGB24,     ///&lt; packed RGB 8:8:8, 24bpp, RGBRGB...
AV_PIX_FMT_BGR24,     ///&lt; packed RGB 8:8:8, 24bpp, BGRBGR...
AV_PIX_FMT_YUV422P,   ///&lt; planar YUV 4:2:2, 16bpp, (1 Cr &amp; Cb sample per 2x1 Y samples)


Additionally you can read https://en.wikipedia.org/wiki/YUV and it’s cited sources and external links.