[opendtv] Re: New Thread: What becomes of Legacy Analog Equipment

Enough to offer another video channel?  Like an AVC program service with
AC-3 audio?

 

Sounds like a ~18-20 percent reduction, on a SDTV program element, so maybe
400-500Kb/sec.  Wow.  

 

John Willkie

 

  _____  

De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Ron Economos
Enviado el: Saturday, December 01, 2007 7:43 PM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: New Thread: What becomes of Legacy Analog Equipment

 

Trust your instincts Bob. Feel the Force. Actually, black and white images
do save bits. When the chroma pixels are all the same value (128) as they
are in a black and white image, they become easily compressible. Even in
an intra picture, it only takes 4 bits to code the chroma in a macroblock
(due to differential encoding of DC coefficients and a short VLC code
for zero difference).

# Macroblock 134  (14, 1) #
       2 Macroblock_Type                               1
       0 Dct_Type                                      0
       0 Dct_Dc_Size_Luminance                         100
       0 Dct_Dc_Size_Luminance                         100
       0 Dct_Dc_Size_Luminance                         100
       0 Dct_Dc_Size_Luminance                         100
       0 Dct_Dc_Size_Chrominance                       00    <---
       0 Dct_Dc_Size_Chrominance                       00    <---
       1 Macroblock_Address_Increment                  1

A typical 4:2:0 MPEG-2 sequence expends on average about 25% of the total
coded DCT coefficient bits on chroma. This makes sense because each
macroblock contains 4 luma blocks and 2 chroma blocks (1 for Cb and 1 for
Cr). Here's a dump of some typical video:

Interactive MPEG Decoder intd 0.72A
@ Statistics output turned on.
@  Found Sequence Start Code at byte position 0.
* --------  Sequence Start Code at 0        ---------
* --------       GOP Start Code at 22       ---------
* --------          Intra frame at 30       ---------
* Frame number: 2              Average mquant: 3.21 
* --- Number of bits used ---
*     High level headers :   8805  (0.79%)
*     Macroblock headers :  47948  (4.29%)
*         Motion vectors :      0  (0.00%)
*       DCT coefficients : 1060563  (94.92%)
*                  Luma  : 820629  (77.38%) 
*                Chroma  : 239934  (22.62%) 
* --- Macroblock types ---
*                  Intra :   8160  (100.00%) 
* --------  Bidirectional frame at 139989   ---------
* Frame number: 3              Average mquant: 4.55 
* --- Number of bits used ---
*     High level headers :   7444  (2.22%)
*     Macroblock headers : 112149  (33.50%)
*         Motion vectors :  95500  (28.53%)
*       DCT coefficients : 119689  (35.75%)
*                  Luma  :  88732  (74.14%) 
*                Chroma  :  30957  (25.86%) 
* --- Macroblock types ---
*                  Intra :     45  (0.55%) 
*          Frame Forward :   1845  (22.61%) 
*          Field Forward :     66  (0.81%) 
*         Frame Backward :   5872  (71.96%) 
*         Field Backward :     27  (0.33%) 
*    Frame Bidirectional :    154  (1.89%) 
*    Field Bidirectional :      8  (0.10%) 
*                Skipped :    143  (1.75%) 
* --------  Bidirectional frame at 182103   ---------
* Frame number: 4              Average mquant: 3.28 
* --- Number of bits used ---
*     High level headers :   7440  (1.67%)
*     Macroblock headers : 131419  (29.47%)
*         Motion vectors :  94157  (21.12%)
*       DCT coefficients : 212895  (47.74%)
*                  Luma  : 160392  (75.34%) 
*                Chroma  :  52503  (24.66%) 
* --- Macroblock types ---
*                  Intra :     35  (0.43%) 
*          Frame Forward :   3908  (47.89%) 
*          Field Forward :     41  (0.50%) 
*         Frame Backward :   3864  (47.35%) 
*         Field Backward :     52  (0.64%) 
*    Frame Bidirectional :    160  (1.96%) 
*    Field Bidirectional :      6  (0.07%) 
*                Skipped :     94  (1.15%) 
* --------      Predicted frame at 238201   ---------
* Frame number: 5              Average mquant: 2.22 
* --- Number of bits used ---
*     High level headers :   7444  (0.83%)
*     Macroblock headers : 126886  (14.19%)
*         Motion vectors : 103744  (11.60%)
*       DCT coefficients : 655924  (73.37%)
*                  Luma  : 494258  (75.35%) 
*                Chroma  : 161666  (24.65%) 
* --- Macroblock types ---
*                  Intra :     58  (0.71%) 
*          Frame Forward :   7721  (94.62%) 
*          Field Forward :    301  (3.69%) 
*                Skipped :     80  (0.98%) 

For black and white encoding, there's 8 (low end for B-frames) to 30 (high
end for I-frames) percent (of the total bit budget per frame) more bits
available for the the luma DCT coefficients.

Ron

Bob Miller wrote:



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