TechSmith Screen Capture Codec 2

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Revision as of 13:12, 7 July 2012 Kostya (Talk | contribs) ← Previous diff		Current revision Kostya (Talk | contribs) (→Frame format)
Line 9:		Line 9:
	0 - frame type (1- coded, 0 - skip frame)		0 - frame type (1- coded, 0 - skip frame)
-	1 - luma quantiser?	+	1 - quantiser1 (0-12)
-	2 - chroma quantiser?	+	2 - quantiser2 (0-12)
	3 - ???		3 - ???
	[macroblock properties]		[macroblock properties]
Line 18:		Line 18:
	4 bytes LE - chunk size		4 bytes LE - chunk size
-	rest - RLE-coded properties in bytes in form (val << 6) | (count)	+	rest - RLE-coded mode in bytes in form (val << 6) | (count)
	Macroblock slices begin with slice size. If the first byte is odd, then it's the full size. Otherwise read whole 32-bit word and divide it by two in order to obtain real macroblock data size.		Macroblock slices begin with slice size. If the first byte is odd, then it's the full size. Otherwise read whole 32-bit word and divide it by two in order to obtain real macroblock data size.
		+
		+	Mode meaning: 0/3 - skip block, 1 - select quantiser1, 2 - select quantiser2
	Macroblocks encode series of 4x4 DCT blocks (4x2), one component after another.		Macroblocks encode series of 4x4 DCT blocks (4x2), one component after another.
Line 50:		Line 52:
	Q2 = 4 * round(quant * 32768 * 0.1313064328597225^2 ) // about 4 * round(quant * 564.966)		Q2 = 4 * round(quant * 32768 * 0.1313064328597225^2 ) // about 4 * round(quant * 564.966)
-	IDCT: (TODO)	+	Unquantising:
		+
		+	val = (quant * (qval << 6) + 0x10000) >> 17
		+
		+	IDCT matrix:
		+
		+	5 5 5 2
		+	5 2 -5 -5
		+	5 -2 -5 5
		+	5 -5 5 -2
	[[Category:Video Codecs]]		[[Category:Video Codecs]]
-	[[Category:Undiscovered Video Codecs]]
	[[Category:Screen Capture Video Codecs]]		[[Category:Screen Capture Video Codecs]]

---

Current revision

• FOURCC: TSC2
• Company: TechSmith

This codec was developed by TechSmith and used in their screen capturing products.

Frame format

This codec operates on 16x8 macroblocks.

 0 - frame type (1- coded, 0 - skip frame)
 1 - quantiser1 (0-12)
 2 - quantiser2 (0-12)
 3 - ???
 [macroblock properties]
 [macroblock slices]

Macroblock properties:

 4 bytes LE - chunk size
 rest       - RLE-coded mode in bytes in form (val << 6) | (count)

Macroblock slices begin with slice size. If the first byte is odd, then it's the full size. Otherwise read whole 32-bit word and divide it by two in order to obtain real macroblock data size.

Mode meaning: 0/3 - skip block, 1 - select quantiser1, 2 - select quantiser2

Macroblocks encode series of 4x4 DCT blocks (4x2), one component after another.

Block format:

 DC - 8 bits for the first block, or VLC (for the difference from the previous DC)
 number of AC coefficients - VLC
 [AC coefficients] - VLC, bottom 4 bits - skip value, top 8 bits - AC value

Scan order is zigzag:

 0  2  3  9
 1  4  8 10
 5  7 11 14
 6 12 13 15

Quantisation:

 Q0 Q1 Q0 Q1
 Q1 Q2 Q1 Q2
 Q0 Q1 Q0 Q1
 Q1 Q2 Q1 Q2

where

 Q0 = 4 * round(quant * 327.68)
 Q1 = 4 * round(quant / 5 * 16384 * 0.1313064328597225) // about 4 * round(quant * 430.265)
 Q2 = 4 * round(quant * 32768 * 0.1313064328597225^2 ) // about 4 * round(quant * 564.966)

Unquantising:

 val = (quant * (qval << 6) + 0x10000) >> 17

IDCT matrix:

 5  5  5  2
 5  2 -5 -5
 5 -2 -5  5
 5 -5  5 -2