Talking about QuickTime playback performance, I was considering
delving deeper to gain more control over playback for the following
When playing uncompressed movies there is a pause whilst QuickTime
I can call a preroll command with a suggested rate and then playback
at that rate starts pretty instantaneously.
This is good, however in my app I cannot predict if the user is
going to play forward or backwards.
So is there a way to preroll preread in both directions so that
either way there is a quick response?
I tried calling Preroll twice with different rates, but the previous
rate is lost.
Not only is the rate lost, but the pre-loaded media data from the
first preroll is thrown away on the second.
Also can I get feedback that the preroll is complete?
If you are calling PrerollMovie yourself, it returns synchronously:
the preroll is complete when it returns.
Whilst playing can I monitor the read ahead buffer to see if there
is a potential under run?
I don't want to get skipped or repeated frames in the movie
playback, so if under-run occurs then I want to abort playback.
There is no "potential" underrun until it actually happens. However,
we are looking into providing a way to detect and report media
underflow errors during playback.
On 19 Dec 2006, at 18:45, Daniel Steinberg wrote:
At 12:43 PM +0100 12/19/06, Guillem Palou wrote:
is there any way to load a movie into ram asyncronously?
Or you have to create your own thread and call this function from there?
LoadMovieIntoRam, like any other movie API, must be called on the
thread that the movie has been opened or migrated to.
However, why do you want to call LoadMovieIntoRam? Do you have any
experimental results to show that this is improving your
performance in any way? In a virtual memory environment, it is
dangerous to preload movie data very far in advance, because you
risk causing pageouts which are far more expensive. The QuickTIme
playback engine manages media read-ahead and the virtual memory
working set pretty rigorously, so in most cases it should be as
good or better to preroll and play the movie than to preload it.
If you have a practical application in which preloading the media
yields demonstrably better results, we'd like to hear about it.
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