GoToMeeting Codec - Revision history

Suxen drol at 08:27, 3 February 2014

2014-02-03T08:27:25Z

← Older revision		Revision as of 01:27, 3 February 2014
Line 424:		Line 424:
	[[Category:Video Codecs]]		[[Category:Video Codecs]]
	[[Category:Incomplete Video Codecs]]		[[Category:Incomplete Video Codecs]]
	~~[[Category:Formats missing in FFmpeg]]~~
	[[Category:Screen Capture Video Codecs]]		[[Category:Screen Capture Video Codecs]]

2013-05-08T02:01:09Z

update samples url due to more samples

← Older revision		Revision as of 19:01, 7 May 2013
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	** G2M2: http://samples.mplayerhq.hu/V-codecs/G2M2/		** G2M2: http://samples.mplayerhq.hu/V-codecs/G2M2/
	** G2M3: http://samples.mplayerhq.hu/V-codecs/G2M3/		** G2M3: http://samples.mplayerhq.hu/V-codecs/G2M3/
	** G2M4: http://samples.~~mplayerhq~~.hu/V-codecs/G2M4/		** G2M4: http://samples.ffmpeg.org/V-codecs/G2M4/

	This is a codec used to save recordings in GoToMeeting. The codec also calls itself GoToWebinar (see [http://www.gotowebinar.com/ http://www.gotowebinar.com/]).		This is a codec used to save recordings in GoToMeeting. The codec also calls itself GoToWebinar (see [http://www.gotowebinar.com/ http://www.gotowebinar.com/]).

2013-05-07T08:02:48Z

ELS values

← Older revision		Revision as of 01:02, 7 May 2013
Line 84:		Line 84:
	==== ELS values ====		==== ELS values ====

	Unsigned values are coded ~~as a number with all bits set to one and an addition to it~~:		Unsigned values are coded using Exponential Golomb notation:

	~~mask = 1;~~		unary prefix + stop bit + remainder, where number of bits in the prefix = number of bits in the remainder
	~~val = 0;~~

	~~while (decode_bit()) {~~
	~~val~~ +~~= mask;~~
	~~mask <<= 1;~~
	}
	~~while (mask > 1) {~~
	~~mask >>= 1;~~
	~~if (decode_bit())~~
	~~val~~ += ~~mask;~~
	}

	E.g. number 5 will be coded as <code>~~11 0~~ 10</code> ~~(i.e. 3 + stop bit + 2)~~.		The unary prefix is coded as n -1 zero bits followed by a one bit. E.g. number 5 will be coded as <code>00 1 10</code>.

	Signed values ~~use last bit for~~ sign:		Here is the decoding algorithm:

			count number of bits in the prefix by reading bits from the arithmetic ELS decoder until a "1" is encountered
			n = number of zero bits in the prefix, i.e "001" ==> n = 2
			read the remainder r as plain binary number of n bits: "10" ==> 2
			value = 2<sup>n</sup> - 1 + r = 2<sup>2</sup> - 1 + 2 = 5

			Signed values are coded as unsigned ones where the LSB indicates the sign:

	if (val & 1)		if (val & 1)

2013-02-20T18:54:48Z

Image decoding

@@ Line 238: / Line 238: @@
      if (flag)
        add_to_cache(L);
+    else
-  //TODO
+      pixel_val = L;
+    for (;;) {
+   }
    if (x > 0) {
@@ Line 260: / Line 304: @@
+       }
+     }
+   }

2013-02-19T20:15:23Z

Image decoding

@@ Line 238: / Line 238: @@
      if (flag)
        add_to_cache(L);
-//TODO
+  //TODO
+   }
    if (x > 0) {
@@ Line 261: / Line 261: @@
+     }
+   }
 === Compression method 2 (ELS image + JPEG) ===

2013-02-19T20:00:39Z

Image decoding

@@ Line 170: / Line 170: @@
 ==== Image decoding ====
    for (y = 0; y < height; y++) {
@@ Line 175: / Line 179: @@
     while (x < width) {
      if (x > 1 && y > 0 &&
-       rgb[x - 1][y] != rgb[x - 2][y] &&
+       rgb[x - 1, y] != rgb[x - 2, y] &&
-       rgb[x - 1][y] != rgb[x ][y - 1] &&
+       rgb[x - 1, y] != rgb[x,     y - 1] &&
-       rgb[x - 1][y] != rgb[x - 1][y - 1] &&
+       rgb[x - 1, y] != rgb[x - 1, y - 1] &&
-       rgb[x - 1][y] != rgb[x - 2][y - 1] &&
+       rgb[x - 1, y] != rgb[x - 2, y - 1] &&
-       pixel_in_cache(rgb[x - 1][y]) {
+       !pixel_in_cache(rgb[x - 1, y])) {
-      rgb[x][y] = decode_pixel_with_prediction(x, y);
+      rgb[x, y] = decode_pixel_with_prediction(x, y);
       x++;
       continue;
@@ Line 187: / Line 191: @@
      if (run_length > 0) {
       // pixel value may get changed here
-      decode_modified_pix(x, y, run_length, &pix);
+      reuse_top_neighbours_if_possible(x, y, run_length, &pix);
-      while (run_length--)
+      while (run_length--) {
-       rgb[x++][y] = pix;
+       rgb[x, y] = pix;
-     } else if (decode_from_cache(&pix)) {
+      x++;
-      rgb[x][y] = pix;
       x++;
      } else {
-      rgb[x][y] = decode_pixel_with_prediction(x, y);
+      rgb[x, y] = decode_pixel_with_prediction(x, y);
       x++;
+     }
+    }
+   }

2013-02-18T20:06:21Z

@@ Line 23: / Line 23: @@
 In general frame is divided into the number of tiles and each tile is coded separately. Usual tile size is 192x128 pixels
 === Chunk C8 ===
@@ Line 78: / Line 80: @@
 === Compression method 1 (ELS image) ===
-===== ELS data =====
+Vanilla augmented ELS coder is used ([http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=582144 The ELS-coder: a rapid entropy coder]) with 36 jots per byte.
-ELS-coded data seems to consist of coded flags and differences for RGB triplets.
+==== ELS values ====
 Unsigned values are coded as a number with all bits set to one and an addition to it:
@@ Line 109: / Line 108: @@
      val = val >> 1;
-Image data is composed this way:
+To make compression better every decoded bit uses a context-depended state, so every bit is decoded this way:
-  single pixel value that is used for transparency colour
+==== Image decoding ====
-Pixels in image can be coded as the one of 10 already decoded neighbours depending on which of them equal to which (a bit like JBIG compression), as some cached value or as the difference to the predicted one from left+top+topleft neighbours.
+  for (y = 0; y < height; y++) {
 === Compression method 2 (ELS image + JPEG) ===

2013-02-18T19:41:46Z

2012-11-04T14:29:58Z

← Older revision		Revision as of 07:29, 4 November 2012
Line 65:		Line 65:
	ELS-coded data seems to consist of coded flags and differences for RGB triplets.		ELS-coded data seems to consist of coded flags and differences for RGB triplets.

	Vanilla augmented ELS coder is used.		Vanilla augmented ELS coder is used ([http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=582144 The ELS-coder: a rapid entropy coder]).
			.

	Unsigned values are coded as a number with all bits set to one and an addition to it:		Unsigned values are coded as a number with all bits set to one and an addition to it:

2012-11-03T08:12:07Z

Compression 2

@@ Line 60: / Line 60: @@
 xxxxx xxxxxxxx xxxxxxxx
 xxxxx xxxxxxxx xxxxxxxx xxxxxxxx
 ELS-coded data seems to consist of coded flags and differences for RGB triplets.
 JPEG data seems to be scan data with escapes but no headers (default Huffman tables and quantisation matrices are used).