Mimic - Revision history

Angustia: Proper interframe description (in pseudo-code)

2008-04-08T22:37:44Z

Proper interframe description (in pseudo-code)

← Older revision		Revision as of 15:37, 8 April 2008
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	* saturate the transformed samples to an unsigned byte range (0..255)		* saturate the transformed samples to an unsigned byte range (0..255)

	The process for decoding an interframe is similar as for an intraframe. Iterate through the planes and the blocks in the same manner. For each block:		The process for decoding an interframe is similar as for an intraframe. Iterate through the planes and the blocks in the same manner. For each block follow this pseudo-code:
	* read 1 bit ~~from the bitstream~~		read 1 bit
	* if ~~the~~ bit is 1 ~~then the~~ block ~~is unchanged~~ from ~~the block at the same position in the~~ previous frame		if bit == 1 for luma plane or bit == 0 for chroma planes
	* if ~~the~~ bit ~~is 0 then the~~ block ~~is to be decoded using the same process~~ as in an intraframe		copy block from previous frame
			else
			if luma plane
			read 1 bit
			if bit == 1
			read 4 bits
			copy block from backreference read in bits
			endif
			endif
			if chroma plane or no backreference
			decode block as in intraframe
			endif

	== Bitstream Packing ==		== Bitstream Packing ==

Angustia: Luma interframes have back references

2008-04-08T22:22:40Z

Luma interframes have back references

← Older revision		Revision as of 15:22, 8 April 2008
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	== Overview ==		== Overview ==
	The Mimic codec operates in a native [[YUV 4:2:0]] colorspace. The codec employs both intraframes and interframes. Each of the 3 planes, Y, U, and V, is encoded separately, in the YVU order. Each plane is broken up into a series of 8x8 blocks. In an intraframe each block, progressing from left -> right, bottom -> top, is transformed using a discrete cosine transform (DCT), quantized, and re-ordered in a zigzag pattern. Finally the transformed non-zero coefficients and the runs of zeros between them are encoded into a bitstream using variable length codes (VLCs). Interframes encode a bit for each block to indicate that the block is unchanged from the block at the same position from the previous frame, or that the block is completely recoded using the same algorithm as each block in the intraframe.		The Mimic codec operates in a native [[YUV 4:2:0]] colorspace. The codec employs both intraframes and interframes. Each of the 3 planes, Y, U, and V, is encoded separately, in the YVU order. Each plane is broken up into a series of 8x8 blocks. In an intraframe each block, progressing from left -> right, bottom -> top, is transformed using a discrete cosine transform (DCT), quantized, and re-ordered in a zigzag pattern. Finally the transformed non-zero coefficients and the runs of zeros between them are encoded into a bitstream using variable length codes (VLCs). Interframes encode a bit for each block to indicate that the block is unchanged from the block at the same position from the previous frame, or that the block is completely recoded using the same algorithm as each block in the intraframe. Luma interframes encode another bit for each block to indicate that the block is unchanged from any of the previous 15 frames. Another 4 bits follow to indicate which frame the back reference refers to.

	Note that this process bears some similarity to [[JPEG]] coding. Notably absent are macroblocks as well as delta coding of DC coefficients.		Note that this process bears some similarity to [[JPEG]] coding. Notably absent are macroblocks as well as delta coding of DC coefficients.

Angustia: Use equivalent fixed point code and rename f to qscale

2008-04-08T22:19:40Z

Use equivalent fixed point code and rename f to qscale

← Older revision		Revision as of 15:19, 8 April 2008
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	Using the quality setting decoded from a Mimic frame's header, compute the block's dequantization factor as:		Using the quality setting decoded from a Mimic frame's header, compute the block's dequantization factor as:

	f = (10000 - quality_setting) * 10 * 9.9999997e-5		qscale = (10000 - quality_setting) / 1001

	If the block being dequantized belongs to a chrominance plane then saturate the dequantization factor between 2.0..10.0. If the block belongs to the luminance/Y plane, saturate the dequantization factor between 1.0..10.0.		If the block being dequantized belongs to a chrominance plane then saturate the dequantization factor between 2.0..10.0. If the block belongs to the luminance/Y plane, saturate the dequantization factor between 1.0..10.0.

Angustia: Emphasize n

2008-04-08T22:12:53Z

Emphasize n

← Older revision		Revision as of 15:12, 8 April 2008
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	53, 60, 61, 54, 47, 55, 62, 63		53, 60, 61, 54, 47, 55, 62, 63
	};		};
	To de-zigzag decoded coefficient n from the bitstream into a 64-element transform matrix:		To de-zigzag decoded coefficient ''n'' from the bitstream into a 64-element transform matrix:

	transform_matrix[zigzag[n]] = decoded_coefficient[n]		transform_matrix[zigzag[n]] = decoded_coefficient[n]

Angustia: Native FFmpeg decoder.

2008-03-22T18:22:23Z

Native FFmpeg decoder.

← Older revision		Revision as of 11:22, 22 March 2008
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	Open source codec library: [http://www.jblinux.net/libmimic/ libmimic]; Note that this website is does not exist as of April 6, 2006. However, the [http://farsight.sourceforge.net Farsight] project incorporates the libmimic source.		Open source codec library: [http://www.jblinux.net/libmimic/ libmimic]; Note that this website is does not exist as of April 6, 2006. However, the [http://farsight.sourceforge.net Farsight] project incorporates the libmimic source.

			FFmpeg has a native decoder for Mimic since r12491.

	== Overview ==		== Overview ==

Angustia: Mimic is bottom-to-top, not top-to-bottom

2008-03-22T18:20:56Z

Mimic is bottom-to-top, not top-to-bottom

← Older revision		Revision as of 11:20, 22 March 2008
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	== Overview ==		== Overview ==
	The Mimic codec operates in a native [[YUV 4:2:0]] colorspace. The codec employs both intraframes and interframes. Each of the 3 planes, Y, U, and V, is encoded separately, in the YVU order. Each plane is broken up into a series of 8x8 blocks. In an intraframe each block, progressing from left -> right, ~~top~~ -> ~~bottom~~, is transformed using a discrete cosine transform (DCT), quantized, and re-ordered in a zigzag pattern. Finally the transformed non-zero coefficients and the runs of zeros between them are encoded into a bitstream using variable length codes (VLCs). Interframes encode a bit for each block to indicate that the block is unchanged from the block at the same position from the previous frame, or that the block is completely recoded using the same algorithm as each block in the intraframe.		The Mimic codec operates in a native [[YUV 4:2:0]] colorspace. The codec employs both intraframes and interframes. Each of the 3 planes, Y, U, and V, is encoded separately, in the YVU order. Each plane is broken up into a series of 8x8 blocks. In an intraframe each block, progressing from left -> right, bottom -> top, is transformed using a discrete cosine transform (DCT), quantized, and re-ordered in a zigzag pattern. Finally the transformed non-zero coefficients and the runs of zeros between them are encoded into a bitstream using variable length codes (VLCs). Interframes encode a bit for each block to indicate that the block is unchanged from the block at the same position from the previous frame, or that the block is completely recoded using the same algorithm as each block in the intraframe.

	Note that this process bears some similarity to [[JPEG]] coding. Notably absent are macroblocks as well as delta coding of DC coefficients.		Note that this process bears some similarity to [[JPEG]] coding. Notably absent are macroblocks as well as delta coding of DC coefficients.
Line 26:		Line 26:
	bytes 17-19 unknown		bytes 17-19 unknown

	The encoded frame begins at byte 20 (counting from 0). To decode an intraframe, iterate through each plane, Y, V, and U. For each plane, iterate through all the 8x8 blocks from left -> right, ~~top~~ -> ~~bottom~~.		The encoded frame begins at byte 20 (counting from 0). To decode an intraframe, iterate through each plane, Y, V, and U. For each plane, iterate through all the 8x8 blocks from left -> right, bottom -> top.

	For each block:		For each block:

Multimedia Mike: /* Bitstream Packing */ another way to word it

2008-03-21T16:16:12Z

Bitstream Packing: another way to word it

← Older revision		Revision as of 09:16, 21 March 2008
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	The Mimic bitstream is packed into 32-bit integers which are then stored in memory and transferred over the network wire in little endian format. To begin reading a packed Mimic bitstream, read the first 32-bit number from memory in little endian format. Read the bits from right -> left within the integer. When those 32 bits are exhausted, the next 4 bytes are read from memory in little endian byte order and the process is repeated.		The Mimic bitstream is packed into 32-bit integers which are then stored in memory and transferred over the network wire in little endian format. To begin reading a packed Mimic bitstream, read the first 32-bit number from memory in little endian format. Read the bits from right -> left within the integer. When those 32 bits are exhausted, the next 4 bytes are read from memory in little endian byte order and the process is repeated.

	~~Basically~~, ~~just bswap32 all~~ the ~~data,~~ and use a ~~normal~~ bitstream reader.		As an alternative reading method, byteswap each 32-bit number in the entire input bytestream and use a standard left -> right bitstream reader.

	== Decoding Coefficients ==		== Decoding Coefficients ==

Angustia: Simpler bitstream packing

2008-03-21T15:48:01Z

Simpler bitstream packing

← Older revision		Revision as of 08:48, 21 March 2008
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	== Bitstream Packing ==		== Bitstream Packing ==
	The Mimic bitstream is packed into 32-bit integers which are then stored in memory and transferred over the network wire in little endian format. To begin reading a packed Mimic bitstream, read the first 32-bit number from memory in little endian format. Read the bits from right -> left within the integer. When those 32 bits are exhausted, the next 4 bytes are read from memory in little endian byte order and the process is repeated.		The Mimic bitstream is packed into 32-bit integers which are then stored in memory and transferred over the network wire in little endian format. To begin reading a packed Mimic bitstream, read the first 32-bit number from memory in little endian format. Read the bits from right -> left within the integer. When those 32 bits are exhausted, the next 4 bytes are read from memory in little endian byte order and the process is repeated.

			Basically, just bswap32 all the data, and use a normal bitstream reader.

	== Decoding Coefficients ==		== Decoding Coefficients ==

Angustia: Yes, the post-processing code is used =)

2008-03-21T05:31:58Z

Yes, the post-processing code is used =)

← Older revision		Revision as of 22:31, 20 March 2008
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	== Post Processing ==		== Post Processing ==
	The open source libmimic package contains an impressive amount of post processing code as well~~. It is not known if any of these functions are actually employed~~.		The open source libmimic package contains an impressive amount of post processing code as well.

	[[Category: Video Codecs]]		[[Category: Video Codecs]]

Angustia: IDCT is the same as used by JPEG

2008-03-21T05:30:47Z

IDCT is the same as used by JPEG

@@ Line 79: / Line 79: @@
 == Inverse Discrete Cosine Transform ==
-To transform a 8x8 matrix, declare 8 temporary integers, v1..v8. For each row (1..8) p in the matrix:
+The IDCT is compatible with JPEG's. It is just different by a factor of 4. By multiplying the input data by 4 and passing the block to JPEG's IDCT, you get the same output as libmimic's code.
 == Post Processing ==