BaseSink and "Subbuffer clipping"

[Benjamin M. Schwartz]

Working on PiTiVi, I noticed some major inaccuracies related to seeking
with PiTiVi's ArraySink element [1].  Reading the BaseSink docs I encountered

"""
Buffers that fall partially in the segment are rendered (and prerolled).
Subclasses should do any subbuffer clipping themselves when needed.
"""

I suspect this may explain our seeking problems.  However, this phrase
("subbuffer clipping") does not appear anywhere else in Google, so I can't
tell quite what I'm supposed to do.

Can someone provide an example of correct "subbuffer clipping" with BaseSink?

Thanks,
Ben

P.S. An example in Python would be ideal, but any language would be helpful.

[1]
http://git.pitivi.org/?p=pitivi.git;a=blob;f=pitivi/elements/arraysink.py;hb=HEAD

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