[M4IF Technotes] Flexibility in resolution in Video levels

[Rob Koenen]

>     When a video level defines a resolution, like 
> Simple   Level 1 with QCIF,
> how much flexibilty is there in distribution of the pixels?  
> 176x144 has 99
> 16x16 blocks.  I gather you can redistribute those blocks to provide a
> different aspect ratio, within some limits.  So, would a 
> 256x96 would be
> allowable if one wanted to stream Ben-Hur?  

yes
> Is there any 
> upper limit to
> this?  Presumably 1584x16 wouldn't be a viable format for 
> mobile devices.

No, there is no upper (extreme) limit. Mobile devices would be able to
decode,
but not display all. But then, MPEG doesn't go as far as the display
in setting its standards.
>     Also, was there any particular reason why non 4:3 resolutions were
> chosen?  192x144 would be a lot more useful for normal 
> content.  Is the
> assumption that the 176x144 would be aspect ratio corrected to 4:3 on
> playback?

These reference resolutions are standard resolutions in image communication 
(CIF, QCIF, ITU- R 601) basically all derived from TV resolutions with 
some compromises between the standards in the different parts of the world.
Rob