Debugging TS input

[Henri Fallon]

With some streams (VOB files streamed by the VLS) I get hundreds of
error messages :

"Skipped macroblock in I-picture"
or
"DCT coeff (non-intra) is out of bounds"

and I get an image every one and a half seconds (almost:)

whereas audio is OK (not even a scratch for this same stream)

How can I ensure the problem is in the vlc and not in the TS produced by
the VLS ?

-- 
henri