I'm afraid you are misunderstanding the purpose of the -t option.
Using the -t option to update a file causes flvmeta to reset
timestamps in the file in order for the FIRST timestamp to be zero, in
case the input file happens to be broken by having a non-zero first
timestamp, for example if it is the result of a badly done file split.
It will never put all keyframe timestamps to a zero value. This would
completely break the FLV file. Why would you want to obtain such a
result ?
Regards,
Marc