--- /dev/null
+UVLC File Specification
+
+Picture Header
+
+ Like in H.263 UVLC start with a PSC (Picture start code) which is 22 bits long
+ 0000 0000 0000 0000 1000 00
+ A PSC is always byte aligned
+ The second information is the picture's format which can be one of following : CIF or VGA (2 bits)
+ 00 : forbidden
+ 01 : CIF
+ 10 : VGA
+ Then comes the picture resolution which is used in combination with the picture's format (3 bits)
+ 000 : forbidden
+ 001 : for CIF it means sub-QCIF
+ 010 : for CIF it means QCIF
+ 011 : for CIF it means CIF
+ 100 : for CIF it means 4-CIF
+ 101 : for CIF it means 16-CIF
+ Then comes the picture's type (3 bits)
+ 000 : INTRA picture
+ 001 : INTER picture
+ Then comes the quantizer's reference for the picture that ranges from 1 to 31 (5 bits)
+ Then comes the frame number (32 bits)
+
+ Picture header is at least 67 bits long
+
+Group of Blocks Header
+
+ Each GOB starts with a GOBSC (Group of Blocks start code) wich is 22 bits long
+ 0000 0000 0000 0000 1xxx xx
+ A GOBSC is always byte aligned. The least significant bytes represent the blockline's number. We can see that PSC
+ means first gob too. So for the first GOB, GOB's header is always omitted.
+
+ Then comes the quantizer's reference for the GOB that ranges from 1 to 31 (5 bits)
+
+ Group of Blocks Header is at least 27 bits long
+
+MacroBlock Header
+
+ Coded Macroblock bit (1 bit)
+ bit 0 : 1 means there's a macoblock, 0 means macroblock is all zero
+
+ Macrobock description code (7 bits)
+ bit 0 : 1 means there's non dc coefficients for block y0
+ bit 1 : 1 means there's non dc coefficients for block y1
+ bit 2 : 1 means there's non dc coefficients for block y2
+ bit 3 : 1 means there's non dc coefficients for block y3
+ bit 4 : 1 means there's non dc coefficients for block cb
+ bit 5 : 1 means there's non dc coefficients for block cr
+ bit 6 : 1 means there's a quantization value following this code
+ bit 7 : Always 1 to avoid a zero byte
+
+ Then comes a differential value for the quantization (2 bits)
+ 00 : -1
+ 01 : -2
+ 10 : 1
+ 11 : 2
+
+
+Block layer
+
+ Codes used for uvlc encoding
+
+ 1/ Run encoding
+
+ coarse | additional | size | value of run | length of run
+ 1 | | 1 | 0 | 1
+ 01 | | 2 | 1 | 1
+ 001 | x | 4 | x + 2 (2:3) | 2
+ 0001 | xx | 6 | xx + 4 (4:7) | 3
+ 00001 | xxx | 8 | xxx + 8 (8:15) | 4
+ 000001 | xxxx | 10 | xxxx + 16 (16:31) | 5
+ 0000001 | xxxxx | 12 | xxxxx + 32 (32:63) | 6
+
+ 2/ Level encoding
+
+ coarse | additional | size | value of level | length of level
+ 1 | s | 2 | 1 | 1
+ 01 | | 2 | EOB |
+ 001 | xs | 5 | x + 2 | 2
+ 0001 | xxs | 7 | xx + 4 | 3
+ 00001 | xxxs | 9 | xxx + 8 | 4
+ 000001 | xxxxs | 11 | xxxx + 16 | 5
+ 0000001 | xxxxxs | 13 | xxxxx + 32 | 6
+ 00000001 | xxxxxxs | 15 | xxxxxx + 64 | 7
+
+ (s stands for sign)
+
+End of Picture header
+
+ A picture ends alwways with a code 0000 0000 0000 0000 1111 11 that is byte aligned and 22 bytes long
+
\ No newline at end of file
projects / mardrone / blobdiff