At 10:00 AM -0700 5/4/04, John Willkie wrote: >You are VERY incorrect. Really? I will disregard this statement and its rudeness,=20 as i do much of what you spout in this forum. =2EI've worked in the MPEG process for years and I=20 know exactly of what I speak. If you were to have=20 included the actual text from the MPEG-2 standard=20 everyone would see just how wrong you are. >MPEG-2 provides several mechanisms that signal video size ans aspect ratio >(section 1: systems), including a flag that signals a video frame as being >1:1.33; 1:1.78 and 1:2.21, and the size relative size of the picture >elements. Look up the extended segment. Correct. From section 6.3.3 of the standard (I do=20 not have the latest version, but I do not think=20 this has been amended). I am only quoting the=20 relevant parts of this section: 6.3.3 Sequence header horizontal_size_value -- This word forms the 12=20 least significant bits of horizontal_size. vertical_size_value -- This word forms the 12=20 least significant bits of vertical_size. horizontal_size -- The horizontal_size is a=20 14-bit unsigned integer, the 12 least significant=20 bits are defined in horizontal_size_value, the 2=20 most significant bits are defined in=20 horizontal_size_extension. The horizontal_size is=20 the width of the displayable part of the=20 luminance component of pictures in samples. The=20 width of the encoded luminance component of=20 pictures in macroblocks, mb_width, is=20 (horizontal_size + 15)/16. The displayable part=20 is left-aligned in the encoded pictures. In order to avoid start code emulation=20 horizontal_size_value shall not be zero. This=20 precludes values of horizontal_size that are=20 multiples of 4096. vertical_size -- The vertical_size is a 14-bit=20 unsigned integer, the 12 least significant bits=20 are defined in vertical_size_value, the 2 most=20 significant bits are defined in=20 vertical_size_extension. The vertical_size is the=20 height of the displayable part of the luminance=20 component of the frame in lines. In the case that progressive_sequence is '1' the=20 height of the encoded luminance component of=20 frames in macroblocks, mb_height, is=20 (vertical_size + 15)/16. In the case that progressive_sequence is '0' the=20 height of the encoded luminance component of=20 frame pictures in macroblocks, mb_height, is=20 2*((vertical_size + 31)/32). The height of the=20 encoded luminance component of field pictures in=20 macroblocks, mb_height, is ((vertical_size +=20 31)/32). The displayable part is top-aligned in the encoded pictures. In order to avoid start code emulation=20 vertical_size_value shall not be zero. This=20 precludes values of vertical_size that are=20 multiples of 4096. aspect_ratio_information -- This is a four-bit=20 integer defined in the Table 6-3. aspect_ratio_information either specifies that=20 the "sample aspect ratio" (SAR) of the=20 reconstructed frame is 1,0 (square samples) or=20 alternatively it gives the "display aspect ratio"=20 (DAR). * If sequence_display_extension() is not=20 present then it is intended that the entire=20 reconstructed frame is intended to be mapped to=20 the entire active region of the display. The=20 sample aspect ratio may be calculated as follows: SAR=3DDAR x horizontal_size/vertical_size NOTE - In this case horizontal_size and=20 vertical_size are constrained by the SAR of the=20 source and the DAR selected. * If sequence_display_extension() is=20 present then the sample aspect ratio may be=20 calculated as follows: SAR=3DDAR x display_horizontal_size/display_vertical_size Table 6-3 - aspect_ratio_information aspect_ratio_information Sample Aspect Ratio DAR 0000 forbidden forbidden 0001 1,0 (Square Sample) - 0010 - 3=F74 0011 - 9=F716 0100 - 1=F72,21 0101 - reserved =BA =BA 1111 - reserved --------- Now, what does all of this mean. =46irst, the standard accommodates two different=20 meanings of aspect ratio, which together can=20 influence the actual display aspect ratio. First,=20 it considers the sample aspect ratio (SAR);=20 second it considers the display aspect ratio DAR. John is correct that the standard does provide=20 values for the common 4:3 and 16:9 aspect ratios=20 as well as 2.21. But this does not limit the=20 ability to designate other SARs or DARs. =46or example, How does MPEG deal with ITU-R BT.601 samples? The size of the raster is stated in=20 horizontal_size and vertical_size. Let's say it=20 is the full 720 x 480/576. But are these samples=20 representing a 4:3 or 16:9 raster. You must look=20 at aspect_ratio_information to figure this out.=20 You can also use any fractional line length in=20 Horizontal size - the display will then stretch=20 the sample to fill the display aspect ratio. =46ortunately "601" is the only video standard in=20 use today that uses variable sample aspect ratio=20 9actually the compressed HD camcorders do this=20 internally, but they always produce square=20 samples at the output. Now how would I designate something other than 4:3 or 16:9 or 2.21:1? Simple. I would use horizontal and vertical size=20 to designate the raster size, and 0001 in aspect_=20 ratio_information to designate square samples.=20 Voila... I can represent ANY aspect ratio. It=20 gets a bit more tricky if I do not use square=20 samples; I would then need to use a reserved=20 extension to indicate the DAR and calculate the=20 SAR using the formulas. John must have been confused by the fact that=20 MPEG took the time to include values for the=20 standards that exist. But this does not mean that=20 you cannot use the standard as I have described. > >ATSC supports only specific video formats, and extended segment support is >specified. > >DVB-SI provides mechanisms -- in addition to MPEG-2 section 1 -- to signal >video frame aspect ratio. > >Wanna try again? Why don't you give up before you make an ass out of yourself again. Regards Craig ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.