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question about the WritePartition method
http://freemxf.org/forum/viewtopic.php?f=2&t=80		 Page 1 of 1
Author:  robert [ Thu May 31, 2007 11:24 am ]
Post subject:  question about the WritePartition method
Hey Matt!

Thank you for the great MXFLib! :)

I have a short question: Is there a possibility to write small parts of the MXF-Body and all ending up in a single partition using the Bodywriter?

The reason for the question is that i would like to abort the writing upon user request. The code should look like (Writer is of class BodyWriter):

Code:
// End header partition
Writer->EndPartition();

while (!Writer->BodyDone()) {
    // write a couple of edit units
    Writer->WritePartition(50,0);

    // check if user wants to abort
    .....
 }


instead of just

Code:
Writer->WriteBody();


which puts everything in one large partition but can take a while to finish. From the documentation and the code in essence.cpp I assume propably yes but I managed to do it only with changes to BodyWriter::WriteEssence and that doesn't seem right :)

Also: I probably overlook some special case, but shouldn't line 2597 in essence.cpp rather be:

Code:
if(ThisSize >= RemainingDuration)


Otherwise always one more edit unit is written than in the WritePartition-Call specified?

Thank you,
best regards,
Robert
Author:  Matt Beard [ Thu May 31, 2007 4:40 pm ]
Post subject: 
The +1 thing is (if my memory serves me correctly) because the last edit unit is stored for next time a body partition is started.

I do like the idea of being able to cancel a write part way through, but this would be quite difficult to make work from within the BodyWriter for clip-wrapping as it passes the entire clip (or details of it!) down to a lower level.

My recommendation would be to write a version of EssenceSource that works as a "filter", passing calls to all methods through to another essence source, but with a hook in GetEssenceDataSize, GetEssenceData and EndOfData to flag that the essence has ended if a test shows that the cancel button has been pressed.

Then rather than:
Code:
BodyStreamPtr MyStream = new BodyStream(OriginalSource);

... you do:
Code:
EssenceSourcePtr NewSource = new FilterSource(OriginalSource);
BodyStreamPtr MyStream = new BodyStream(NewSource);
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