Index: docs/nut4cc.txt
===================================================================
--- docs/nut4cc.txt	(revision 668)
+++ docs/nut4cc.txt	(working copy)
@@ -101,6 +101,38 @@
 RGB[48] Packed RGB 16:16:16, 48bpp, 16R, 16G, 16B, the 2-byte value for each R/G/B component is stored as little-endian [NOT in AVI]
 [48]RGB Packed RGB 16:16:16, 48bpp, 16R, 16G, 16B, the 2-byte value for each R/G/B component is stored as big-endian    [NOT in AVI]
 
+Since many exotic planar YUVA pixel formats are not contemplated by
+AVI/QuickTime FourCC list, the following scheme is adopted for
+representing them.
+
+The first two bytes can contains the values:
+Y1 = only Y
+Y3 = YUV
+Y4 = YUVA
+YA = Y+A
+
+The third byte represents the width and height chroma subsampling
+values for the UV planes, that is the amount to shift the luma
+width/height right to find the chroma width/height.
+
+The fourth byte is the number of bits used (8, 16, ...).
+
+If the order of bytes is inverted, that means that each component has
+to be read big-endian.
+
+Follows the list of the supported YUVA planar format FourCCs created using this scheme:
+
+Y1[00][16]  Planar gray, 16bpp, little-endian [NOT in AVI]
+[16][00]1Y  Planar gray, 16bpp, big-endian    [NOT in AVI]
+Y3[11][16]  Planar YUV 4:2:0, 24bpp, (1 Cr & Cb sample per 2x2 Y samples), little-endian [NOT in AVI] 
+[16][11]3Y  Planar YUV 4:2:0, 24bpp, (1 Cr & Cb sample per 2x2 Y samples), big-endian    [NOT in AVI] 
+Y3[10][16]  Planar YUV 4:2:2, 32bpp, (1 Cr & Cb sample per 2x1 Y samples), little-endian [NOT in AVI] 
+[16][10]3Y  Planar YUV 4:2:2, 32bpp, (1 Cr & Cb sample per 2x1 Y samples), big-endian    [NOT in AVI] 
+Y3[00][16]  Planar YUV 4:4:4, 48bpp, (1 Cr & Cb sample per 1x1 Y samples), little-endian [NOT in AVI] 
+[16][00]3Y  Planar YUV 4:4:4, 48bpp, (1 Cr & Cb sample per 1x1 Y samples), big-endian    [NOT in AVI]  
+Y4[11][ 8]  Planar YUV 4:2:0, 20bpp, (1 Cr & Cb sample per 2x2 Y & A samples)            [NOT in AVI]
+YA[00][ 8]  8bit gray, 8bit alpha [NOT in AVI]
+
 Raw audio: [x] is an byte with value x,  [NOT in AVI]
 ALAW    A-LAW
 ULAW    MU-LAW