mpeg2 program stream 720×576 anamorphic results in 720×404 ???

[Dennis Couzin]

Heh! I sent a 1920×1080 8-bit uncompressed 4:2:2 file into Compressor for mpeg-2 compressor and the QuickTime player says the mpeg-2 is 720×404. The mpeg-2 looks great when played with Streamclip.

If you think about it, DCT compressed video has no inherent pixel count. Look at Figure 1 in Tudor.The 64 pixels in the image aren’t really represented by a 64 coefficient DCT block. Tudor’s text oversimplifies, while his figure is correct. The path shown snaking through the coefficients actually makes an increasing triangle based on relevance (roughly measured by u+v). The snaking path gets truncated in the compression, but a triangle is never a block.

The image pixels disappear in a DCT compression and other, non-corresponding, things take their place. In decompression, pixels are created. Why then is QuickTime player reporting 720×404? Does its mpeg-2 decompression algorithm always create 720×404 pixels, and leave further pixel creation to a scaling algorithm? Is that why it has even number 404 vertically rather than 405 (as 16:9 proportion requires)? Working with Apple software is a guessing game.