detect '4MV' encoded blocks?

[plugh]

Is there a tool that will scan an encode and report if any blocks were encoded with 'four motion vectors per macroblock'?

If not, can anyone suggest a simple way to detect this? Is this something indicated in (for example) a vop header, or do you have to drill down and inspect the macroblocks?

Thanks!

[Manao]

You have to parse the whole stream.