INTERNAL: MPEG movie will not play in Window's viewers, but plays fine on Mac and Unix viewers

Many windows players can only playback what is called the Constrained Parameter Bitstream format of MPEG-1.

From the MPEG FAQ:

Can MPEG-1 encode higher sample rates than 352x240x30 or 352x288x25?

It seems to be the number one misconception about MPEG-1: that it has fixed or limited frame size, i.e. 352x240x30 fps or 352x288x25 fps. In fact MPEG-1 can use any frame size, including CCIR-601 resolutions (704x480), with frame sizes as high as 4095x4095x60 fps. MPEG-2 is more limited since frame sizes must be multiples of 16.

The misconception apparently arises from the standard profile, a kind of subset known as Constrained Parameters Bitstream (CPB), which is a series of restrictions that the MPEG-1 stream must meet, including bit rate and frame sizes. Most (maybe all) hardware decoders accept only streams that follow the CPB profile.

You can encode with any bit rate or frame size and you still have standard MPEG-1; you just can't say it meets the standard profile or whatever, and you probably can't play it with some existing decoder chips.

Where did they get 352x240 ?

That derives from the CCIR-601 digital television standard which is used by professional digital video equipment. It is (in the US) 720 by 243 by 60 fields (not frames) per second, where the fields are interlaced when displayed. (It is important to note though that fields are actually acquired and displayed a 60th of a second apart.) The chrominance channels are 360 by 243 by 60 fields a second, again interlaced. This degree of chrominance decimation (2:1 in the horizontal direction) is called 4:2:2. The source input format for MPEG I, called SIF, is CCIR-601 decimated by 2:1 in the horizontal direction, 2:1 in the time direction, and an additional 2:1 in the chrominance vertical direction. And some lines are cut off to make sure things divide by 8 or 16 where needed. For 50 Hz display standards (PAL, SECAM) change the number of lines in a field from 243 or 240 to 288, and change the display rate to 50 fields/s or 25 frames/s. Similarly, change the 120 lines in the decimated chrominance channels to 144 lines. Since 288*50 is exactly equal to 240*60, the two formats have the same source data rate.

What are Constrained Parameters Bitstreams?

CPB are a limited set of sampling and bitrate parameters designed to normalize computational complexity, buffer size and memory bandwidth while still addressing the widest possible range of applications. CPB limits video to 396 macroblocks (101,376 pixels) per frame if the frame rate is less than or equal to 25 fps ( frames per second), and 330 macroblocks (84,480 pixels) per frame if the frame rate is less or equal to 30 fps. Therefore, MPEG video is typically coded at SIF dimensions (352 x 240 x 30fps or 352 x 288 x 25 fps).

The total maximum sampling rate is 3.8 Ms/s (million samples/sec) including chroma. The coded video rate is limited to 1.862 Mbit/sec. In industrial practice, the bitrate is the most often waived parameter of CPB, with rates as high as 6 Mbit/sec in use.

Why are Constrained Parameters Bitstreams so important?

It is an optimum point that allows (just barely) cost effective VLSI implementations in 1992 technology (0.8 microns). It also implies a nominal guarantee of interoperability for decoders and encoders. MPEG devices which are not capable of meeting SIF rates are not canonically considered to be true MPEG.

Are there ways of getting around Constrained Parameters Bitstreams for SIF class applications and decoder?

Yes, some. Remember that CPB limits frames to 396 macroblocks (as in 352 x 288 SIF frames). 416 x 240 x 24 Hz sampling rates are still within the constraints, but this only aids NTSC (240 lines/field) displays. Deviating from 352 samples/line could throw off many decoder implementations that have limited horizontal sample rate conversion modes. Due to chip die size constraints (most chips barely pack in the necessary features), many decoders use simple doubling, e.g. 352 to 704 samples/line via binary taps which are simple shift-and-add operations. Future MPEG decoders will have arbitrary sample rate converters on-chip. Also remember that the 1.86 Mbit/sec limit is often ignored in real life.

As far as viewers are concerned, Vmpeg is a freely distributable MPEG player that is not plagued by the above idiosyncrasy. It has nice controls not found on the Window players (like adjusting the frame rate, play all frames, etc.) and it will play MPEG-1 and MPEG-2. Download at:

http://www.perry.com/resources.html

Each location provides an executable that will install Vmpeg on your Windows system.