Quicktime File Format (2012-08-14).pdf

Media Data Atom TypesVideo MediavertOff_D (denominator)A 32-bit signed integer containing either the denominator portion of the vertical offset or the number1.Video Sample DataThe format of the data stored in video samples is completely dependent on the type of the compression used,as indicated in the video sample description. The following sections discuss some of the video encodingschemes supported by QuickTime.Uncompressed RGBUncompressed RGB data is stored in a variety of different formats. The format used depends on the depth fieldof the video sample description. For all depths, the image data is padded on each scan line to ensure that eachscan line begins on an even byte boundary.●●●●For depths of 1, 2, 4, and 8, the values stored are indexes into the color table specified in the color tableID field.For a depth of 16, the pixels are stored as 5-5-5 RGB values with the high bit of each 16-bit integer set to0.For a depth of 24, the pixels are stored packed together in RGB order.For a depth of 32, the pixels are stored with an 8-bit alpha channel, followed by 8-bit RGB components.RGB data can be stored in composite or planar format. Composite format stores the RGB data for each pixelcontiguously, while planar format stores the R, G, and B data separately, so the RGB information for a givenpixel is found using the same offset into multiple tables. For example, the data for two pixels could berepresented in composite format as RGB-RGB or in planar format as RR-GG-BB.Uncompressed Y´CbCr (including yuv2)The Y´CbCr color space is widely used for digital video. In this data format, luminance is stored as a single value(Y), and chrominance information is stored as two color-difference components (Cb and Cr). Cb is the differencebetween the blue component and a reference value; Cr is the difference between the red component and areference value.This is commonly referred to as “YUV” format, with “U” standing-in for Cb and “V” standing-in for Cr. This usageis not strictly correct, as YUV, YIC, and Y´CbCr are distinct color models for PAL, NTSC, and digital video, butmost Y´CbCr data formats and codecs are described or even named as some variant of “YUV.”2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.169