I found a workaround here: It says, I can trim the first field in avisynth like this: Avisource:("mysource.avi") AssumeTFF() SeparateFields() Trim(1,0) Weave() AssumeTTF() I changed the last line from AssumeBFF() to TFF(). Both work for me, I see no difference. It also works without the last Assume line. If anyone sees a problem with this workaround please let me know. Also, if anyone knows a way to encode to utvideo avi without the field problem to begin with.