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This Technical Note contains a collection of archived Q&As relating to a specific topic--questions sent the Developer Support Center (DSC) along with
answers from the DSC engineers. Current Q&As can be found on the Macintosh Technical Q&As web site.
[Oct 01 1990]
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QuickTime rotation and skew aren't implemented
Date Written: 1/22/93
Last reviewed: 7/2/93
We can't apply the rotation and skew effects to a QuickTime 1.5 movie. We've
created an identity matrix, applied RotateMatrix to the matrix, set the matrix
to the movie using SetMovieMatrix, and played the movie. The movie didn't
rotate but the movieRect rotated and the movie scaled to the movieRect. Is
there anything wrong with what we're doing?
Rotation and skew will give you correct results for matrix operations but they
haven't been implemented into QuickTime movie playback yet. Scaling and offset
transformations now work with movies and images; rotation and skew are
important future directions. Meanwhile, you can accomplish rotation and skewing
by playing a movie to an off-screen GWorld and then using QuickDraw GX to
display the rotated or skewed off-screen GWorld.
Back to top QuickTime 1.6 fixes GetMoviePosterPict bug
Date Written: 1/11/93
Last reviewed: 6/14/93
I'm opening a movie document and using NewMovieFromFile to get a movie. When I
try to get the poster for the movie I get back a paramErr (-50) from the
GetMoviesError call and a NIL picHandle from GetMoviePosterPict. If I use
Quicktime 1.0 everything works fine but QuickTime 1.5 gives me the paramErr. Am
I doing something wrong or is there a bug?
You're hitting your head against a QuickTime 1.5 bug that (as far as we can
tell) has no reasonable workaround. It has to do with asking for the PICT from
a movie at a time (movie time) that falls in between differentiated frames of
the same size. The problem has been identified and fixed in QuickTime 1.6.
Back to top Multiple EnterMovies and ExitMovies vs ExitToShell
Date Written: 3/16/93
Last reviewed: 6/24/93
The QuickTime 1.0 documentation says I can EnterMovies multiple times, as long
as I balance each EnterMovies with ExitMovies. But the article in issue 13 of
develop says, "Don't call ExitMovie. ExitToShell does this for me." So now the
only call I have to use is EnterMovies. But this seems to destroy the balance
of these routines. What should I do?
Good question. I should have mentioned something about the case in which
multiple EnterMovies. The way EnterMovies works is that it creates a new
QuickTime environment if the current a5 world doesn't have one already. If the
current a5 world already has one from a previous EnterMovies call, then nothing
is done except that a counter is incremented to keep track of the number of
times EnterMovies has been called. The original reason for this was to account
for DAs which use an application's a5 world. By doing this, if an application
has called EnterMovies already, the movie toolbox knows that it doesn't have to
reinitialize when the DA calls EnterMovies. Then, when the DA calls ExitMovies,
it decrements the counter and as long as all EnterMovies and ExitMovies calls
are balanced, the Movie Toolbox won't dispose of the QuickTime world until the
last ExitMovies call is made.
The reason we suggest not to call ExitMovies is that ExitToShell will
automatically call ExitMovies for you. By doing so, you can avoid some of the
problems that developers have had with disposing of movie structures improperly
and in the wrong order. Letting ExitToShell do the final cleanup avoid these
problems because the entire a5 world and heap is disposed of as well.
But, if you've nested EnterMovies and ExitMovies calls, this is what we recommend:
- If you're writing an application, call
EnterMovies and don't call
ExitMovies. This way, any external that uses the same a5 world and calls
EnterMovies and ExitMovies will simply increment a counter and then decrement
the counter and do nothing else.
- If you're writing an external that runs under someone else's application,
you have two choices:
- Call
EnterMovies and never call ExitMovies. This causes QuickTime to
initialize once during the first call to any of your externals. The counter
will keep incrementing whenever you call EnterMovies but the final ExitToShell
will still clean things up. The counter is a long so unless your external gets
called more than 2 billion times, don't worry about an overflow problem.
- Call
EnterMovies in the beginning of each external and ExitMovies at the
end of each external. This can cause a lot of wasted CPU time if the main
application (or someone else in the a5 world) didn't call EnterMovies first
because each of the EnterMovies calls in your externals will require QuickTime
to reinitialize. The reason for this is that you balance every EnterMovies and
the corresponding ExitMovies will dispose of the QuickTime world. This can be
very bad if you external gets called often. On the other hand, if your external
has a initialization routine and close routine that is called before and after
all your other routines, you can call EnterMovies in the initialization
routine, and then call ExitMovies in your close routine. Of course, each of the
routines called in between could call either EnterMovies and ExitMovies, or not
call either of them at all. But, this depends on your implementation.
Back to top Check whether 'vdig' supports off-screen digitizing
Date Written: 1/7/93
Last reviewed: 6/14/93
When we try to digitize frames (grabbed using QuickTime) into an off-screen
pixmap, our VDGrabOneFrame call crashes. How would you suggest I digitize into
an off-screen pixmap?
You need to check whether or not the 'vdig' resource supports digitizing to
off-screens by calling the VDPreflightDestination call! If the
PreflightDestination call with an off-screen destination fails, then you need
to digitize to a window on the digitizing device, and then copy (using CopyBits
or your own algorithm for speed) the image from the window to your off-screen.
Some 'vdig' resources don't support digitizing to off-screen directly because
their hardware does the digitization asynchronously. So, your application will
have to do some extra work in some cases. (You should always preflight your
destination before setting it with SetPlayThruDestination.)
Back to top Techniques for controller to go to beginning or end
Date Written: 11/24/92
Last reviewed: 3/1/93
The controller constants have been left out of the latest Movies.h header for
Goto beginning and ending commands. Only mcGotoTime is left. Is it OK to use
these constants or is there a newly defined and accepted way to do this now?
Scanning the interfaces, we can't locate a time when the controller had actions
to go to the beginning or end. In any case there are two ways of accomplishing
the same objective: The first is to use the MCActionGotoTime and pass the zero
to go to the start of the movie and the result from GetMovieDuration to go to
the end of the movie. The code to do this gets a little bit cumbersome since
you have to pass a TimeRecord. This may be why our favorite is the second method.
Second, to go to the start, call GoToBeginningOfMovie followed by
MCMovieChanged. And to go to the end, call GoToEndOfMovie also followed by
MCMovieChanged. The following routine shows how to accomplish what you want:
void DoGotoEnds(short direction)
{
WindowPtr window;
DocRecHandle wHndl;
if (window = FrontWindow()) { /* don't bother if no movies to play */
if (IsAppWindow(window)
&& (wHndl = (DocRecHandle)GetWRefCon(window)) ) {
switch (direction) {
case gotoBeginning:
GoToBeginningOfMovie( (*wHndl)->wMovie);
break;
case gotoEnd:
GoToEndOfMovie( (*wHndl)->wMovie );
break;
default:
return; /* do nothing if came here on error */
break;
}
MCMovieChanged ((*wHndl)->wPlayer, (*wHndl)->wMovie);
}
}
}
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Doing this you let the Movie Toolbox take care of all the details and the
results are the same. MCMovieChanged is needed in order to make the controller
aware of the different state.
As a bonus, the following code shows (in a different scenario) how you can fill
in the time record necessary for the MCActionGoto call in case that's the route
you want to take:
/* selects the whole movie for editing */
void DoSelectAll(void)
{
WindowPtr window;
DocRecHandle wHndl;
ComponentResult err;
TimeRecord tRec;
if (window = FrontWindow()) { /* don't bother if no movies to play */
if (IsAppWindow(window) && (wHndl = (DocRecHandle)GetWRefCon(window)) ) {
if ( MCIsEditingEnabled((*wHndl)->wPlayer)) {
tRec.value.lo = tRec.value.hi = 0;
tRec.base = 0;
tRec.scale = GetMovieTimeScale((*wHndl)->wMovie);
if ( err = MCDoAction((*wHndl)->wPlayer,
mcActionSetSelectionBegin, &tRec)) {
DebugStr("\pError trying mcActionSetSelectionBegin");
}
tRec.value.hi = 0;
tRec.value.lo = GetMovieDuration((*wHndl)->wMovie);
tRec.base = 0;
tRec.scale = GetMovieTimeScale((*wHndl)->wMovie);
if ( err = MCDoAction((*wHndl)->wPlayer,
mcActionSetSelectionDuration, &tRec)) {
DebugStr("\pError trying mcActionSetSelectionDuration");
}
}
}
}
}
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Back to top Getting QuickTime playback frame rate on the fly
Date Written: 11/24/92
Last reviewed: 6/14/93
I need both to get and set frames/sec for my frames-per-second playback rate
menu. GetMovieRate and SetMovie rate seem too transient to use since the movie
has to be currently playing and the effect leaves once it stops. The PreferredRate
calls look good but are only scalars. How do I get the real frames/second and how do
I actually set a rate that the controller will honor when the Play button is pressed?
At the moment there are no facilities to ascertain the real frame rate while
the movie is playing. The view from engineering is that with enough interest
and good reasons for this to be a feature, it may get into a future version of
QuickTime but at the moment it can't be done.
Setting the rate is even more remotely in the future. As you know, the movie
toolbox drops frames as needed to keep pace with the passing of time. This is a
self-regulating process and there's no way to tell the toolbox how many frames
you want to see because it may not be able to deliver based on certain conditions.
Back to top Interleave QuickTime 1.5 movie sound and video data
Date Written: 11/20/92
Last reviewed: 3/1/93
Our product's sound/video synchronization is way off with QuickTime 1.5; it
worked perfectly with QuickTime 1.0. The video can't keep up with the sound,
especially on the full-screen movies. The movies are playing much slower with
1.5. Isn't QuickTime 1.5 supposed to make movies play faster?
Your movies probably aren't properly interleaved. When you add sound to a movie
using SoundToMovie, the sound is added to the end of the video data. We
recommend that sound and video be interleaved so that the hard drive doesn't
have to spend extra time seeking between media that store video and media that
store audio on a hard drive. The data handler prefers to be able to
sequentially read through a movie file. This is especially important for slower
Macintosh models that don't have the extra CPU and SCSI access speed to spare.
QuickTime can accommodate for some noninterleaved data by caching an entire
sound track of a movie if small enough. However, the size of a cache is
internal to QuickTime and can't be depended on. It's possible that different
QuickTime versions could have different cache sizes since we've been
recommending that video and sound movies be interleaved. The result could be
that the extra disk-seeking time has caused sound and video to be out of sync
for slower machines such as the Macintosh LC.
One way to check interleaving is to resave the movie using Movie Converter (or
some other program that flattens movies) in a flattened format. Movie Converter
uses QuickTime's FlattenMovie call to do this. The steps Movie Converter takes
are: choose Save As, select Make Movie Self-Contained, and Save to a new movie
file. This new movie should play back with correct video and sound sync.
You can actually see the problem if you examine the movie with MovieShop, a
program that lets you deal with QuickTime movies at a movie data level. For
example, if you select the Play information button that's in the window after
you open a movie, the program will display a time graph showing you where the
video and sound data are saved in the continuous data stream. If the movie is
interleaved, the green (for video) and red (for sound) indicators are interleaved.
If the movie isn't interleaved, the green indicators are clumped together in the
beginning of the file, and the red indicators (for sound) are at the end.
The latest version of MovieShop and documentation is available on this issue's
CD. MovieShop and information relating to this Q&A are discussed in the
article "Making Better QuickTime Movies" in this issue.
Back to top Saving a movie's active selection
Date Written: 11/2/92
Last reviewed: 6/14/93
I have a movie with two video tracks: Track #1--Enabled, Duration=10; Track
#2--Disabled, Duration=20. I set the movie's active segment to (0, 10) and
saved the movie resource to a movie file. When I open the movie in MoviePlayer,
the movie is played for the time value of 20, ignoring the active segment and
there being one enabled track with a duration of 10. Short of creating a new
movie from a selection of the above mentioned movie, is there any way to get
MoviePlayer to do what I'd expect and not ignore the active segment and play
past the enabled track's duration?
The active selection isn't saved along with a movie. Therefore, no application
will be able to restore and play back the active segment. You'd have to create
a new movie from the selection in order to get MoviePlayer or any other application
to play that selection only. If users will be using your application to play back the
movie, you could store information regarding the active segment in a user data atom
inside the movie. You could then have your application load the user data atom if it
exists inside a movie when it's opened, to restore the selection. That would be the
only way to save the active movie selection.
Back to top How to get movie frame time parameter for GetMoviePict
Date Written: 9/9/92
Last reviewed: 3/1/93
How do I find the correct time values to pass to GetMoviePict, to get all the
sequential frames of a QuickTime movie?
The best way to find the correct time to pass to get movie frames is to call
the GetMovieNextInterestingTime routine repeatedly. Note that the first time
you call GetMovieNextInterestingTime its flags parameter should have a value of
nextTimeMediaSample+nextTimeEdgeOK to get the first frame. For subsequent calls
the value of flags should be nextTimeMediaSample. Also, the whichMediaTypes
parameter should include only tracks with visual information, 'vide' and
'text'. Check the Movie Toolbox chapter of the QuickTime documentation for
details about the GetMovieNextInterestingTime call. For a code example, see the
revised SimpleInMovie on your
developer CD. The routine to look at is called DoGetMoviePicts in the file
SimpleInPicts.c.
Back to top Determining QuickDraw video media pixel depth
Date Written: 8/18/92
Last reviewed: 6/14/93
How do I get the pixel depth of the QuickTime video media for a given track?
To find the video media pixel depth, you'll need to retrieve the media's image
description handle. You can use GetMediaSampleDescription to get it, but this
routine needs both the video media and the track's index number. It's not
obvious, but a media's type is identified by its media handler's type. Thus,
you can walk through a movie's tracks by using its indexes until you find video
media, at which point you have both the track index and video media.
The following sample code does the trick:
Media GetFirstVideoMedia(Movie coolMovie, long *trackIndex)
{
Track coolTrack = nil;
Media coolMedia = nil;
long numTracks;
OSType mediaType;
numTracks = GetMovieTrackCount(coolMovie);
for (*trackIndex=1; *trackIndex<=numTracks; (*trackIndex)++) {
coolTrack = GetMovieIndTrack(coolMovie, *trackIndex);
if (coolTrack) coolMedia = GetTrackMedia(coolTrack);
if (coolMedia) GetMediaHandlerDescription(coolMedia,
&mediaType, nil, nil);
if (mediaType = VideoMediaType) return coolMedia;
}
*trackIndex = 0; // trackIndex can't be 0
return nil; // went through all tracks and no video
}
short GetFirstVideoTrackPixelDepth(Movie coolMovie)
{
SampleDescriptionHandle imageDescH =
(SampleDescriptionHandle)NewHandle(sizeof(Handle));
long trackIndex = 0;
Media coolMedia = nil;
coolMedia = GetFirstVideoMedia(coolMovie, &trackIndex);
if (!trackIndex || !coolMedia) return -1; // we need both
GetMediaSampleDescription(coolMedia, trackIndex, imageDescH);
return (*(ImageDescriptionHandle)imageDescH)->depth;
}
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Back to top QuickTime 1.5 fixes GetMoviePict grayscale images -157 error
Date Written: 8/27/92
Last reviewed: 6/14/93
Trying to read any single frame (except the first) from a grayscale (4, 16, or
256 grays), QuickTime movie gives a -157 error (invalid pixel depth). I do
"framehandle = GetMoviePict(damovie,daunitnum)" and test if it's 0. If so, then
I do "io = GetMoviesError()" and it gives me the -157 error. GetMoviePict is
working fine for all color and black/white movies. It just doesn't work on
"Animation" grayscale and "Video" grayscale movies. Is this a bug?
With QuickTime 1.0, grayscale images cause a -157 error with GetMoviePict; some
grayscale images may work if the color tables are custom made (ImageDescription
structure clutID is 0). However, QuickTime 1.5 fixes this problem.
Back to top Determining whether a movie is set to loop or not
Date Written: 8/11/92
Last reviewed: 3/11/93
How does Simple Player determine whether a movie is set to loop or not? Movie
files that are set to loop seem to have a string of 'LOOP' at the end of the
'moov' resource. Does Simple Player check 'LOOP'?
Simple Player identifies whether movies are set to loop by looking within the
user data atoms for the 'LOOP' atom, as you've noticed. It's a 4-byte Boolean
in which a value of 1 means standard looping and a value of 0 means palindrome
looping. Your applications should add the user data 'LOOP' atom to the end of
the movie when a user chooses to loop. We recommend this method as a standard
mechanism for determining the looping status of a movie. If the 'LOOP' atom
doesn't exist, there's no looping. The calls you need to access this information
are GetMovieUserData, GetUserData, AddUserData, and RemoveUserData, as defined in
the Movie Toolbox chapter of the QuickTime documentation. For more information see
the Macintosh Technical Note "Movies 'LOOP' Atom and Friends."
Back to top Passing a refCon to the movie controller action filter proc
Date written: 7/22/92
Last reviewed: 6/14/93
Is there a way that the action filter proc of a QuickTime movie controller
component can have a user reference field so that I can know which
movie-"object" the movie controller is referring to? There are local variables
associated with a particular movie that I would like to access from the action
filter proc; currently there's no way to reference back to the variables in my
program except through globals.
This was a difficult task under QuickTime 1.0, requiring you to stuff some sort
of pointer in the movie user data fields. The good news is that at developer
requests, QuickTime 1.5 includes a new call in the Movie Controller suit
allowing you to pass and receive a long value when you set up your filter proc
as follows:
pascal ComponentResult MCSetActionFilterWithRefCon (MovieController mc,
MCActionFilterWithRefCon blob, long refCon) = {0x2F3C,0x8,0x2D,0x7000,0xA82A};
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The proc is of the form:
pascal Boolean userPlayerFilter(
MovieController mc,
short action,
void *params,
long refCon);
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The proc returns TRUE if it handles the action, FALSE if not. The "action"
parameter identifies the action to be executed; "params" is the set of
potential parameters that go with the action; and "refCon" is any long value
passed to MCSetActionFilterWithRefCon.
Back to top Problem with disabling a movie video track
Date Written: 5/29/92
Last reviewed: 6/14/93
When I disable a track in a movie, another random track becomes disabled as
well. Is this a QuickTime bug?
This was a QuickTime 1.0 bug, but it's fixed with QuickTime 1.5. With QuickTime
1.5 it's no longer necessary to work around the bug, since disable now works.
Back to top 'pnot' resource format for QuickTime-like preview in dialog box
Date Written: 3/6/92
Last reviewed: 1/11/93
I would like to implement the preview/thumbnail feature in the Standard File
dialog, just like the extension included with QuickTime. Is that code available
separate from QuickTime? If not, could I at least get information on how the
preview is created?
To implement your own preview/thumbnail feature, simply duplicate the Standard
File dialog, add the necessary 'DITL' resources, and install a custom filter
procedure for handling preview commands. On the System 7 CD there's an example,
StdFileSample, that shows exactly how to create a custom file dialog. The
Macintosh Technical Note "Customizing Standard File" describes how to do this
as well. For generating and displaying the preview, you can use the following
PreviewResourceRecord, found at the end of the ImageCompression.h file:
struct PreviewResourceRecord {
unsigned long modDate;
short version;
OSType resType;
short resID;
};
typedef struct PreviewResourceRecord PreviewResourceRecord;
typedef PreviewResourceRecord *PreviewResourcePtr, **PreviewResource;
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This is the format for the 'pnot' resource, which defines the preview for the
movie file, usually pointing to a 'PICT' resource. It's all you need to
generate QuickTime-compatible preview without using QuickTime.
Back to top QuickTime alias and FSSpec system services under System 6
Date Written: 3/3/92
Last reviewed: 6/14/93
I recall reading that QuickTime includes an implementation of the Alias Manager
for System 6, but I haven't found any precise description of what's included.
Is it a bare minimum to support QuickTime? Or is the full Alias Manager there?
Also, is there any way I can use the FSSpec interface to the File Manager, or
must I revert to the System 6 interface?
When QuickTime is installed, most of the Alias Manager is available in System 6,
with these exceptions:
NewAlias will accept a fromFile parameter, but it never creates a relative alias.NewAliasMinimalFromFullPath and ResolveAliasFile aren't available.ResolveAlias and UpdateAlias will accept a fromFile parameter, but ignore it.MatchAlias may be called, but the kARMMultVols, kARMSearchMore, and kARMSearchRelFirst flags aren't available. If you pass them in, they'll be ignored. Furthermore, if you pass in a matchProc, it will never be called.- The System 6 Alias Manager won't mount network volumes.
To summarize, in System 6 the Alias Manager doesn't handle relative aliases,
multiple volume searches, "searchMore" searches, and network volume mounting.
On the bright side, nearly all calls are present. Aliases created in System 6
are compatible with System 7 aliases, and aliases created in System 7 will work
in System 6.
Unfortunately, QuickTime doesn't currently install an Alias Manager Gestalt
selector, since it's only a partial implementation. You can check for the Alias
Manager using Gestalt and, if it isn't present, look for QuickTime (using
Gestalt); if QuickTime is present, assume you have an Alias Manager, subject to
the limitations listed above.
QuickTime also makes extensive use of the FSSpec data structure introduced in
the System 7 File Manager. Nearly all the FSSpec calls are available in System
6 when QuickTime is installed. The following calls are available in System 6,
and should behave as documented for System 7: FSMakeFSSpec, FSpOpenDF,
FSpOpenRF, FSpCreate, FSpDirCreate, FSpDelete, FSpGetFInfo, FSpSetFInfo,
FSpSetFLock, FSpRstFLock, FSpRename, FSpCatMove, FSpOpenResFile, FSpCreateResFile,
and FSpGetCatInfo. FSpExchangeFiles isn't available when using the QuickTime System 6
version of the FSSpec calls.
Again, the Gestalt selector for the FSSpec calls isn't installed when QuickTime
is there. This means that the gestaltFSAttr Gestalt selector may not be present, and
gestaltHasFSSpecCalls may not be set, even if gestaltFSAttr is present.
Back to top Displaying thumbnail PICT
Date Written: 2/21/92
Last reviewed: 1/5/93
How can I display the thumbnail of the PICT instead of some generic icon when I
create QuickTime PICT files? This would really help with distinguishing files
when someone wanted to create a movie and had a lot of these PICTs around.
You need to follow these four steps:
1. Get the thumbnail. You can use either the MakeThumbnailFromPicture or
MakeThumbnailFromPictureFile routines as listed in the ImageCompression
interface file. It will pass back the PicHandle for the thumbnail. To install
into the Finder, you need some resources (ICN#, ics#, icl8, ics8, icl4, ics4).
2. Make the thumbnail into a 'icsx' format to store it as a resource. (Please
see MakeIcon on the Developer CD. It is not modified for pichandles so you may
have to add a DrawPicture. Basically, you need to create a GWorld and create
the appropriate 16- or 32-bit image.)
3. Add icons to resource. You can use the basic Resource Manager's
WriteResource and AddResource calls to add the resource.
4. Set Finder bits: Stuff icon resources into the file itself with resource ID
kCustomIconResource, and set the hasCustomIcon bit.
{ myCInfoPBRec.ioFlFndrInfo.fdFlags :=
BOR(myCInfoPBRec.ioFlFndrInfo.fdFlags, $0400) }.
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Back to top QuickTime 1.0 FS6Patch elucidation
Date Written: 2/10/92
Last reviewed: 6/14/93
The FS6Patch description in the QuickTime 1.0 CD Read Me file says, "There is a
known bug with HFS on System 6." What specifically is this bug? According to
the Read Me file, "The exact situation under which the problem occurs is
somewhat rare." What is the exact situation? "If the patch is not necessary, it
will not install itself." What criteria is used to determine necessity?
With QuickTime 1.5 the patch has been incorporated into the QuickTime file
instead of being a separate file, but the functionality, described below, is
the same.
When closing or flushing a file that has multiple open paths to a given fork,
it is possible that the blocks marked as available for the other paths can also
be allocated to the other fork. If this happens before the other paths are
closed, blocks will be mapped to more than one fork, potentially trashing at
least one of them.
The condition that can trigger this condition is multiple writeable paths to
the same fork. Once this is satisfied you would need to make some changes to
the fork, close the path, use any of the other paths to modify the fork, access
the other fork and modify data. If all these things happen you could see the
damage to one of the forks (the second-to-last being accessed).
The code that loads the patch checks the system first; the range where the
patch is used is 6.0.4 < system < 7.0. The version of the ROM is also
used to decide when to install. If the ROM indicates the machine is later than
the Macintosh IIfx, then a fix in ROM is assumed. The last check is to see if
the code being patched is already in RAM (the assumption is that being in RAM
means fixed). If so, the patch doesn't get used.
Back to top QuickTime track and movie sound volume
Date Written: 2/3/92
Last reviewed: 1/11/93
What do the values of a movie's or track's volume represent? Is there no way to
make a track louder?
Here's the scoop: The volume is described as a small fract 8:8 and its values
go from -1 to 1 with negative values as placeholders. The maximum volume you
can get is 0x0100 with the minimum being 0 (or any negative value). The
advantage of using negative volumes is that you can turn off sound while
maintaining the level of volume. For example, -1 and 0 both equate to no
volume, but the -1 implies that 1 should be the volume when sound is turned
back on, whereas the 0 does not.
The volume for a track is scaled to the movie's volume, and the movie's volume
is scaled to the value the user specifies for the speaker volume using the
Sound control panel. This means that the movie volume represents the maximum
loudness of any track in the movie.
Back to top SetMovieRate and controlling movie playback rate
Date Written: 1/27/92
Last reviewed: 1/11/93
QuickTime is a joy! But I've run aground with SetMovieRate. I am trying to
change the rate at which a movie plays back, but if I call SetMovieRate the movie
starts playing immediately, the controller goes wild, and the next time I hit the
play button it ignores the previous rate. How can I control my playback rate?
SetMovieRate takes effect immediately that is why your movies start playing as
soon as you make the call with a rate not zero. Also calling the movie toolbox
directly to change the state of a movie associated with a controller is a sure
way to confuse the controller, causing the controller, for example, to show the
play button when the movie is playing.
QuickTime 1.5 introduced a change in the movie controller which makes it use
the current preferred movie rate when the user hits the play button. To change
the normal playing rate you'll need to call SetMoviePreferredRate and let the
controller do the rest.
Note that with QuickTime 1.0 the movie controller plays movies at rate of one
(0x00010000) whenever the user hits the play button, regardless of the current
preferred rate.
For details on filter procedures, controller actions, and the movie controller
in general, see the "QuickTime Components" chapter of the QuickTime Developer's Guide.
Back to top Clipping QuickTime movie posters
Date Written: 12/10/91
Last reviewed: 1/11/93
Our application uses the movie poster as a still frame in a cell, similar to
using a PICT. If a user sizes the cell width so that it's narrower than the
poster, even though we clip the drawing to the cell size, QuickTime posters
draw their full width, writing over whatever is in the way. Pictures clip
through DrawPicture; why doesn't ShowMoviePoster stay within the clipping
region?
ShowMoviePoster, as well as the movie and preview showing calls, uses the movie
clipping characteristics rather than the destination port's clipping region.
You must set the movie's clipping region to obtain the results you want. An
easier way to do this is to get the picture for the poster by calling
GetMoviePosterPict, and then simply use DrawPicture to display the poster.
Because this is just a picture, the clipping region of the port is honored.
This way you don't need different code for movies and pictures.
Back to top PutMovieIntoHandle and data forks
Date Written: 12/10/91
Last reviewed: 6/14/93
I save PICTs to my document's data fork by writing the contents of the PicHandle.
To save movies, do I convert the movie to a handle, and then save that as I would with PICTs?
I just want the file references, not the data itself.
To save movies that are suitable for storage in a file, use PutMovieIntoHandle.
The result of this call can be saved in the data fork of your files, and then
you can call NewMovieFromHandle to reconstruct the movie for playback or editing.
You should also read the documentation regarding the Movie Toolbox FlattenMovie
procedure, which creates a file that contains the 'moov' resource and the data
all in the data fork. The advantage here is that the movie file you create
using FlattenMovie can be read by any other QuickTime-capable application.
Back to top QuickTime and sound channel deallocation
Date Written: 12/2/91
Last reviewed: 1/11/93
Our QuickTime application gets a Sound Manager error -201 after playing movies
in succession, apparently because sound channels used in the previous movies have
not been reclaimed. How does QuickTime decide to deallocate sound channels? It doesn't
seem to happen in my "while (!IsMovieDone(theMovie) && !Button())" play loop.
Sound channels are released by active movies when they notice that some other
movie needs them. This is currently done only at MoviesTask time. Before entering
your loop to play a single movie, you can do one or both of the following:
- Preroll the movie you're about to play and check the error. If preroll
returns -201, call
MoviesTask(0,0) to give the other active movies a chance to
give up their sound channels. A subsequent preroll of theMovie should return noErr.
- Call
SetMovieActive(otherMovies, FALSE). Deactivate the movies that you
aren't playing to force them to give up their resources.
Back to top Standard controller with MCCut or MCClear
Date Written: 11/25/91
Last reviewed: 1/11/93
When I select all frames in QuickTime and then do an MCCut or MCClear, the
standard controller gets larger and redraws itself at the top of the movie. Is
this a situation I should be prepared to handle or a bug? Does the controller
behave strangely when the selectionTime of a movie is -1 or when the duration
of the movie is 0?
The behavior you're observing is to be expected if the controller is attached
to the movie. In this case, the controller goes to wherever the bottom left
corner of the movie box takes it. If the movie loses all its "visible" parts,
the movie controller will jump to the top of the window. The only way to get
around this is to detach the controller when the movie box is empty; this is
also something to keep in mind for the cases when the movie contains only
sound, since pure sound movies have no dimensions. You can find sample code
showing how to do this on the Developer CD Series disc, in the
SimpleInMovies example that accompanies the QuickTime article in
develop Issue 7.
Back to top MCSetClip and clipping with the movie controller
Date Written: 11/15/91
Last reviewed: 6/14/93
I use SetMovieDisplayClipRgn to set my movie clip, but the movie doesn't obey
my clipping. Does the movie controller component ignore this clipping?
You probably are directly modifying a movie that is attached to a controller
without notifying the controller of the changes. The controller uses the
display clip for its own purposes, such as for badges.
If you want to do clipping with the movie controller you must use MCSetClip.
MCSetClip takes two regions. The first clips both the movie and the controller.
The second clips just the movie, and is equivalent to the movie display clip.
If both clips are set, the controller does the right thing and merges them as
appropriate. If you don't want one or the other of the clips, set them to zero.
In general, if you are going to do something to a movie that is attached to a
controller you must either do it through the controller, using the action calls,
or you must call MCMovieChanged. Otherwise, the controller would need to
constantly poll the movie to see if its state changed. Clearly this would be
Evil and Slow.
Back to top How to get the first video frame
Date Written: 10/11/91
Last reviewed: 6/14/93
Stepping through QuickTime movie video frames in the order they appear in the
movie is simple using GetMovieNextInterestingTime, except for getting the first
frame. If I set the time to 0 and rate to 1, I get the second frame, not the
first. In addition, the video may start later than at 0. How do you suggest
finding this first frame of video?
To get the first frame under the conditions you describe, you have to pass the
flag nextTimeEdgeOK = $2000 to GetMovieNextInterestingTime. What this flag does
is make the call return the current interesting time instead of the next, if
the current time is an interesting time. You need to do this because there's no
way to go negative and then ask for the next interesting time.
Back to top Status of rotating matrix support
Date Written: 10/11/91
Last reviewed: 1/11/93
What's the status of RotateMatrix and its use with SetMovieMatrix and
SetTrackMatrix?
RotateMatrix works fine. But rotating matrixes are not supported for movies or
images. So, although RotateMatrix will give you the correct mathematical
result, unless you are using the matrix to transform something else (as with
TransformFixedPoints) it has little use.
Rotation is a very important direction that is sure to get more attention in
the future.
Back to top QuickTime 1.5 supports user-defined media types
Date Written: 10/10/91
Last reviewed: 1/11/93
Can I add a media to a QuickTime movie that is not video or audio? If so, is
there anything special I need to do to add text notes that can potentially
accompany each frame in my "movie," which can follow the video frames if a user
edits the movie in any way?
QuickTime version 1.0 allows for only video and sound media. There's no way to
install your own type, even in a case so obvious as the one you mention. Adding
other media types is a high QuickTime priority and is likely to make it in a
future release, but currently there's no mechanism to do it.
Back to top QuickTime file audio retrieval
Date Written: 9/17/91
Last reviewed: 6/14/93
How can I retrieve audio from QuickTime files in 1-second chunks? I need a
sound equivalent of GetMoviePict.
QuickTime 1.5 allows you to retrieve sound from a movie (or a single track from
a movie) using the call ConvertMovieToFile. The developer QuickTime 1.5 CD
contains a sample that shows how to do this; the path is "QuickTime 1.5:
Programming Stuff: SampleCode: ImportExportMovie."
With QuickTime 1.0, you must write your own audio extraction routine, using
GetMediaSample to collect the sound data by hand and the SoundDescription data
structure to (1) find frequency, format, and other details, (2) help you figure
out how many samples you need for a second, and (3) fill in the resource data fields.
See the QuickTime documentation for detailed information on ConvertMovieToFile.
The best source of information on sound resources and such is the Sound Manager
chapter in Inside Macintosh Volume VI.
Back to top QuickTime Movie Toolbox "globals" are stored in system heap
Date Written: 6/6/91
Last reviewed: 6/14/93
According to the QuickTime Movie Toolbox documentation, "The Movie Toolbox
maintains a set of global variables for every application using it." How much
global memory is required? Our application is shy on global data space.
The information maintained is not kept with the application's global variables.
The handle created by the EnterMovies call is stored in the system heap, not in
the application heap. You don't have to worry about how much space to allocate
in your application. This initialization does not affect your A5 world either.
EnterMovies initializes everything, including setting up the necessary data
space and creating a handle to it. When you're done, be sure to make a call to
ExitMovies to clean up the QuickTime data.
If an application makes multiple calls to EnterMovies, a different set of
"globals," or data area, is set up for each call. A call to ExitMovies should
be made before exiting the area that made the call to EnterMovies. For example,
an application that uses QuickTime will call EnterMovies and set up the
QuickTime world. Then an external may be called upon that wants to use
QuickTime. This external would have to make a call to EnterMovies to set up
another QuickTime world for its use. Before leaving, the external should call
ExitMovies to clean up after itself. The application can then continue to use
QuickTime with the original world it set up.
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