I have a movie-reader baded on the QTPixelBufferVCTToCGImage sample.
It works except that it is NOT TIMING-SAFE ---- if buffer processing
is delayed, buffers will be overwritten by later images even though
they are retained and the address locked! You can get by with that
for simple movie players, but it is unacceptable for more complex
applications. This is a generic problem for all Quicktime movie-
reading applications using this approach.
CVPixelBufferPools should not recycle CVPixelBuffers (or their backing
memory) while they are still retained. If you have a reproducible
case where this is happening, please write a bug report and attach
sources, compiled executable and media that we can reproduce it with.
The problem occurs because the PixelBufferPool used during
decompression apparently has an "aging" mechanism controlled by
kCVPixelBufferPoolMaximumBufferAgeKey It "ages" the pixel buffer by
moving it back into the available-buffer queue even though it is
locked. This is a bug.
That's not what the mechanism is for. The aging clock starts when the
buffer is released back into the pool. If you retain the buffer, it
should not be recycled.
I am looking for help to work around this by disabling the aging
mechanism----but I can not see how to get to the pixel buffer pool
in order to set the kCVPixelBufferPoolMaximumBufferAgeKey value.
(The type of the number to be set is not obvious either even though
the value is zero.)
Are you absolutely certain that there isn't a bug in your code that
releases the buffers earlier than you intended? It would be a shame
to put a lot of energy into working around a bug that you could fix
directly.
Sam Bushell
QuickTime Engineering
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