FFDShow is already known for it issues (including for example mentioned one). Today’s featured one is related to its Video Decoder. A great deal of FFDShow related issues amy be worked around with a single shot by listing the image name as an FFDShow exclusion under registry:
but I felt relaxed and the problem re-occurred from Windows service where HKEY_CURRENT_USER was not available/applicable.
FFDShow Video Decoder registration looks like:
It is immediately clear that the filter registered with extremely (and definitely unreasonably, breaking guidelines) high merit in conjunction with generic video media type will be taken as a possible decoder in every single graph rendered. At the very least, this is a perofrmance issue, similar to frequently reported like this recent one: How to reduce time during pin connection on vista ultimate using RenderStream function…?.
However the real problem was that the filter was accepting connection on my source pin and pretending it could be a valid decoder instead my own one (definitely registered with a proper merit of 0×00800000 (MERIT_PREFERRED). Did it actually decode? No, just sent blackness on the output… It seems that it is getting a good manner to distance from this crapware by implementing IAMGraphBuilderCallback interface on the graph builder site and reject consideration of FFDShow A/V Decoders as candidates.