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Re: Corrupted movie ?

>we have a very serious issue here with some qt movies that we create in
>our application.
>we create the movie, we add video tracks, effects, etc..., then we save
>it using
>OpenMovieFile, UpdateMovieResource then CloseMovieFile.
>
>Sometimes, for some unknown reason, the movie file is corrupted when we
>try to reload it in our editor, or in the Movie Player. Sometimes it
>crashes the player and sometimes a msg box says 'cannot open file
>xxxx.mov because invalid media data was found in the movie'.
>
In most cases, some memory related bugs lurking in your code are the
reason for
such problems. QT is very stable, and along the years, the basic functionality
of movie creation proved itseld solid.
>I have two questions
>
>1) is it acceptable, with QT, to create a _lot_ of video tracks and
>effects in the same movie ? Maybe there are known issues when there are
>too many of them...? It's not unusual for our movies to contain >100
>tracks. Sometimes when there are a lot of tracks, the playback suddenly
>crashes deep into some QT code (in 'decompressVideoFrame', but i've
>seen crashes elsewhere,too...)...

Well.. It is possible, but not recommended to have such a movie. Many times,
having such a huge number of tracks means your not using QT in the best way.
Many times one track could "do" what you use 20 for... I never stressed
QT into
such a huge movie structure, so there may be QT bugs you encounter.

One important thing --- when dealing with so many tracks, QT will need
LOTS AND LOTS
of memory. as an estimate, calculate the memory needed for a video frame,
(e.g. 320x240 pixel video frame takes 300KB with 4 bytes per pixel), then
multiply this
by the number of your tracks. this means, you need at least 30-40MB just
for QuickTime to
maintain your 100 tracks movie!

Lack of memory may be the reason for the corruption.
>
>2) Is there an application that would allow us to have a look at our QT
>movies and maybe check where the problem is ?
>

There are many applications that do this. Some even are free. The one i
recommend is called
"Dumpster" and is available as part of the QT SDK CD. I think you can
also download it as a
QT Development tool from Apple's developers site.

This utility allowes you to browse the atoms of a movie structure, and to
see the tracks,
the media, the sample tables, and all.

Another such utility is "MovieAnalyzer" but it's quite old, and will not
provide information
about newer media and track types (effects for example).

Motti Shneor,
CEO, suMac LTD.
Software Development for the Macintosh
------
ceterum censeo microsoftiem delendam esse
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