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In 1991, creating a QuickTime
movie player or editor was relatively straightforward. Back
then, there were two types of media to work with -- video
and sound -- and a canvas of APIs. At the time, QuickTime
demos featured trees swaying in the wind, clouds rolling
overhead, and the moon cascading its light down through an
evening sky -- and the movies were postage stamp size! Not
the most compelling examples of multimedia. Now, don't get
me wrong. I love QuickTime, but I'm glad those days are
over!
Today, QuickTime delivers the most dynamic media
available -- professional quality video and sound, MPEG, 3D
objects, sprites, text and MIDI, and its capabilities are
continuing to grow. With QuickTime 2.5, it is easier now for
movie tracks to act on one another, as is the case with our
Tween track, which sends its information to another track to
change it dynamically over time. The possibilities for
truly exposive media content are there, yet so many
QuickTime applications act as though we are still back in
1991 and can only deal with video and sound tracks. Well
folks, it's many years later and it's time to get with the program.
This Technote explains how you can make sure your
QuickTime application isn't blind to any media types
available to it and some simple things you can do with that
media to add value to your application.
Updated: [Dec 20 1996]
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Identifying the Media
Some applications, in an effort to make sure they can
successfully edit or otherwise manipulate a particular
movie's data, will take a look at the movie's media to see
what types are available. In general, this was fine in the
early days, since video and sound were the first two
pioneering media types of the QuickTime frontier. But now,
with the burgeoning of new media types, QuickTime
applications are not necessarily taking full advantage of
their capabilities by looking for particular media types.
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Using GetMovieIndTrackType
Instead of looking for a specific media type, you should
be looking for a media characteristic. In QuickTime 2.0,
Apple introduced GetMovieIndTrackType() for
this explicit purpose. You can use this call to conveniently
find those tracks which draw and those which play sound
using the two flags, VisualMediaCharacteristic
and AudioMediaCharacteristic. For the standard
media types that are included with QuickTime 2.5,
VisualMediaCharacteristic will pick out the
following types of tracks: Video, MPEG, Sprite, QuickDraw3D,
Text, TimeCode. AudioMediaCharacteristic will
pick out: Sound, Music, MPEG. (MPEG is somewhat of a special
case, since it can contain both sound and video data in one
stream and hence one track.)
Not only can you use GetMovieIndTrackType to
find tracks that share a common media characteristic, but
you can also use it to find tracks that share a particular
media type when you really need that information. Which
search method you employ is controlled by the flags that you
pass into the last parameter of the call. A fully
parameterized call to look for tracks with media that has a
video characteristic would look like:
theTrack = GetMovieIndTrackType(sourceMovie, trackIndex, VisualMediaCharacteristic,
movieTrackCharacteristic);
whereas a fully parameterized call to look for tracks
with media of a certain type would look like:
theTrack = GetMovieIndTrackType(sourceMovie, trackIndex, VideoMediaType,
movieTrackMediaType);
You might use one of these calls in a routine like this:
Track theTrack;
long trackIndex = 0;
while(theTrack = GetMovieIndTrackType(sourceMovie, ++trackIndex,
VisualMediaCharacteristic, movieTrackCharacteristic)) {
// theTrack meets your search request so do something with it
}
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Note:
You can use either movieTrackMediaType
or movieTrackCharacteristic but not
both in a single call to
GetMovieIndTrackType(); you can
combine, however,
movieTrackEnabledOnly with either
call. Also, the trackIndex value is not equal to a
track's number. Rather, it is an indexed value of
the tracks found that meet your criterion.
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Using Video Media
Video media is one of the first things you think about
when working with QuickTime, since so many "movies" are
pictures and sound. Video media can be found by calling
GetMovieIndTrackType(), using either the
VideoMediaType or
VideoMediaCharacteristic flags. While basically
all QuickTime applications deal with video media in one way
or another, there are several cool things that you can do to
take advantage of some new as well as some old QuickTime features.
First Cool Thing: Using
SetTrackClipRgn()
You can use SetTrackClipRgn() to apply an
interesting or aesthetic frame to a video track. Many
developers have shied away from this feature because
clipping typically slows down QuickTime movie playback and
may affect the overall presentation. However, there are
several QuickTime acceleration cards available today that
have hardware assistance for clipping, scaling and color
conversion, thus unburdening QuickTime from having to make
these modifications itself. And, of course, today's
PowerMacs are really starting to scream. Unless you're going
for full-screen, full-motion video, many PowerMacs can
handle the overhead of applying and using a track clip
region. Which leads to my second point about scaling and translation.
Second Cool Thing: Using
SetTrackMatrix()
Using SetTrackMatrix(), you can scale and
distort (but not yet rotate) your video track in interesting
ways. Again, with today's video cards, many can provide
hardware assistance in this operation, giving you creative
flexibility like you haven't had before.
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Note:
While both the track's clip region and matrix can
be set statically using either of the
aforementioned calls, both can be changed
dynamically by using a Tween track.
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More recently introduced are the concepts of Track
References and Modifier Tracks. One way to provide more value to video
tracks is to add a text track which has descriptions of the various
parts of the video track. This idea has been promoted since the Text
track's introduction in QuickTime 1.5. Initially, the thought was to add
a text track to act as subtitling for movie dialog or as descriptive
text to identify a scene or sound clip. But now text tracks have a new
capability when you are using the Movie Controller interface. Text
track data can now be used as chapter or scene descriptors with its info
being displayed in a pop-up menu in the Movie Controller play bar.
Typically, the text track is hidden or disabled, although the track can
be displayed as well (its utility and aesthetic quality would seem to
detract from the controller's function). In order to get the movie
controller to display the chapter name in the play bar, you must create
a reference between the text track containing the scene names and one or
more of the other tracks in the movie. This is done using
AddTrackReference. In the example below, the reference is
added from a video track to the text track. It could also be added from
a sound track, an MPEG track - just about any type.
AddTrackReference(videoTrack, textTrack, 'chap', nil);
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Sound Media
QuickTime sound tracks have a media type of
SoundMediaType and have an
AudioMediaCharacteristic. The use of QuickTime
sounds has been enhanced over the years with the introduction of new
sound compression methods. This has enabled the use of much higher
quality and quantity of audio in applications and multimedia titles. It
is also just starting to enable some new possibilities in using this
media type over the Internet.
Moving Sound Around
Yes, just playing sounds hardly stands out today. And since you have a
few new controls at your fingertips that can make your sound more
dynamic, it just might be time to start exercising that option. Using
MediaSetSoundBalance(), you can adjust the left-to-right
balance of any track that has an AudioMediaCharacteristic. Setting the
balance is hardly a new concept, but how it gets used in an application
is something to discuss. For regular audio playback, it's reasonable to set
the sound balance once and leave it for the duration of the program.
However, in the case where you need dynamically changing sounds, you can
still use QuickTime and the convenient QuickTime movie file container by
utilizing the MediaSetSoundBalance() call.
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Text Media
QuickTime Text tracks have a media type of
TextMediaType and have a
VisualMediaCharacteristic. Much of the power of
the Text track is in how it adds value to other QuickTime media. In
reading the other sections of this Note, you'll get an idea of some of
the power of Text media.
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MPEG Media
MPEG media in QuickTime has had a dual life for some
time. On the one hand, there has been support for MPEG media
within QuickTime since version 2.0. The other hand is the
'but' as in "...but QuickTime 2.0 requires a special
hardware decoder board to see or hear that MPEG media in QuickTime."
Today, there is good news for QuickTime, MPEG and those
developers who want to take advantage of both because of the
introduction of the QuickTime MPEG Extension for Power
Macintosh. This extension lets all Power Macs play and use
MPEG media, type MPEGMediaType, as a full
fledged citizen in the QuickTime world. But MPEG is unique
among the media types in that it can contain either video or
sound media or both. This is why it is so important to use
the MediaCharacteristic flags to find appropriate media to
deal with, since you wouldn't want to miss out on using the
versatile MPEG media type. To be certain that you'll find MPEG
media when it's available use either the
AudioMediaCharacteristic flag,
VisualMediaCharacteristic flag or both flags when checking
the tracks' media characteristics.
When you do get down to work with MPEG media that has video information,
you might want to take advantage of a nice capability of the QuickTime
MPEG Extension. It has the ability to set a rectangular clip region on
visual MPEG media without any performance penalty. This can be
especially useful for poorly captured and encoded MPEG media that show
visual garbage along the edges of the video frame - unfortunately, an
all too common occurence. Using scaling and clipping during runtime can
handily hide the glitch.
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QuickDraw3D Media
QuickDraw3D media, recently introduced with QuickTime
2.5, has a media type of ThreeDeeMediaType and
has a VideoMediaCharacteristic. Besides being
unique because its sample data is made up of 3D objects,
QuickDraw 3D media is also very interesting because of its
relationship to the various other media types. Besides being
unique because its sample data is made up of 3D objects, QuickDraw 3D
media is also very interesting because of its relationship to the
various other media types. With most other media, new sample data is
needed over time to see or hear anything as a movie plays. Although you
can approach using QuickDraw 3D data the same way, it is much more
powerful to use the new Tween track (in QuickTime 2.5) and its sample
data to override QuickDraw 3D objects, lights and cameras, therefore
animating a 3D model using relatively little data bandwidth. Also, it is
possible to map the data from video tracks onto the surface of a
QuickDraw 3D object in a QuickTime movie - and the video track can play
and change as you might expect, all while being blasted onto the face of
a 3D object. How's that for interesting?!
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Sprite Media
QuickTime Sprites may be the most misunderstood media
type that QuickTime supports, probably because its elements
do not necessarily have to be confined to a timeline or run
from beginning to end. But, to get started, you can think of
using QuickTime Sprites in the traditional way -- a linear
track moving from start to finish -- then grow from that point.
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QuickTime Music (MIDI) Media
QuickTime Music, often thought of as MIDI, has been
available in QuickTime since version 2.0 but has recently
been significantly enhanced in QuickTime 2.5.
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Summary
QuickTime, being more versatile and powerful today, calls out to
your application to take full advantage of its capabilities Some
people may think that flipbook animations, such as those provided by
Java and animated GIFs, are the great. Well, I thought they were
great, too, in 1987 when VideoWorks first came out, but with all the
VERY COOL features that QuickTime 2.5 offers today, it is almost a
crime against humanity not to do something with them. Therefore, you
ought to use some of the methods discussed in this Note to find and
manipulate the new media types. That way, your app can be the best it can be!
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References
Inside Macintosh: QuickTime
QuickTime 2.0 SDK Documentation
QuickTime 2.1 Developer Note
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Downloadables
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