[Mp4-tech] MPEG-4 part 2, issue with vop_time_increment_resolution and vop_time_increment parameters

[daniele renzi]

Dear Experts,

when debugging an MPEG-4 part 2 proprietary encoder, I've encountered a problem when using a value for vop_time_increment_resolution equal to 8 or 16.

The spec ISO/IEC 14496-2 says:
"fixed_vop_time_increment:  This value represents the number of ticks between two successive VOPs in the display order. The length of a tick is given by vop_time_increment_resolution. It can take a value in the range of [0,vop_time_increment_resolution). The number of bits representing the value is calculated as the minimum number of unsigned integer bits required to represent the above range...".
The same is valid for the vop_time_increment parameter.
If I understood correctly the spec, e.g. when vop_time_increment_resolution is equal to 8, the number of bits for encoding (fixed_)vop_time_increment would be 3, as the highest value (vop_time_increment_resolution) of the range is not included.

On the contrary it seems that certain players (e.g. QuickTime) assert a number of bits equal to 4 in such a case.
I've also found the following thread on the web:
http://lists.apple.com/archives/QuickTime-Users/2007/Sep/msg00030.html

Can anyone confirm that my assumption (number of bits = 3 when vop_time_increment_resolution is equal to 8) is correct?
If so, I think that the bug mentioned in the above link is real. Could you please confirm that?

Thanks in advance.

Best regards,

Daniele


Daniele Renzi
bSoft
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