Question

What follows is an initializer method. It creates a Movie structure from a file, with an eye to extracting the raw pixels for processing, as per Apple QA1443. This is then wrapped in a QTMovie – sourceMovie = [QTMovie movieWithQuickTimeMovie: ...] – for convenience.

After initializing such an object, the second method is called, and we attempt to use sourceMovie. However, it turns out that any attempt to access sourceMovie here results in EXC_BAD_ACCESS For instance, NSLog(@"%@", sourceMovie) is impossible. The movie appears to have been deallocated, although it is not clear why.

Furthermore, in this second method, the usual methods to obtain a CVPixelBufferRef do not properly function: QTVisualContextIsNewImageAvailable seems always to return NO, and QTVisualContextCopyImageForTime always gives you an imageBuffer pointing at 0x00. (I guess this is not surprising if the QTMovie, Movie or visualContext are somehow being deallocated.)

The question then is, why is sourceMovie inaccessible from the second method? Is it being deallocated as it seems? If so, why?

And now the code, and sorry in advance for the length.

// From the .h, we have the following inst var declarations:
Movie                    myMovie;
QTMovie                  *sourceMovie;
QTVisualContextRef        visualContext;
CVPixelBufferRef         imageBuffer;
pixels_xy                sourceSize;
MovieAnalyzer            *analyzer;

// And now to the @implementation...

-(id)initWithFileString:(NSString *)file {
    if (self = [super init]) {
        NSError *e;

        // Bit of a hack - get the movie size using temporary QTMovie.
        sourceMovie = [QTMovie movieWithFile:file error:&e];
        if (e) {
            [self release];
            NSLog(@"Could not open movie.");
            return nil;
        }

        NSSize movieSize = [[sourceMovie posterImage] size];
        CGRect bounds = CGRectMake(0, 0, movieSize.width, movieSize.height);

        // Save the size in pixels.
        sourceSize.x = (int)movieSize.width, sourceSize.y = (int)movieSize.height;

        CFStringRef movieLocation = (CFStringRef) file;

        // Get a QT Visual Context, and create a movie inialized to use it for output.
        visualContext = NULL;
        OSStatus status = CreatePixelBufferContext(k32ARGBPixelFormat, &bounds, &visualContext);
        if (noErr != status && NULL == visualContext) {
            [self release];
            NSLog(@"Problem initializing QT Visual Context.");
            return nil;
        }

        /*** Instantiate the Movie ***/
        myMovie = NULL;
        Boolean trueValue = true;
        QTNewMoviePropertyElement newMovieProperties[3] = {0};

        // Setup movie location
        newMovieProperties[0].propClass = kQTPropertyClass_DataLocation;
        newMovieProperties[0].propID = kQTDataLocationPropertyID_CFStringPosixPath;
        newMovieProperties[0].propValueSize = sizeof(CFStringRef);
        newMovieProperties[0].propValueAddress = &movieLocation;

        // Assign the visual context - could also be NULL
        newMovieProperties[1].propClass = kQTPropertyClass_Context;
        newMovieProperties[1].propID = kQTContextPropertyID_VisualContext;
        newMovieProperties[1].propValueSize = sizeof(visualContext);
        newMovieProperties[1].propValueAddress = &visualContext;

        // Make the movie active
        newMovieProperties[2].propClass = kQTPropertyClass_NewMovieProperty;
        newMovieProperties[2].propID = kQTNewMoviePropertyID_Active;
        newMovieProperties[2].propValueSize = sizeof(trueValue);
        newMovieProperties[2].propValueAddress = &trueValue;

        status = NewMovieFromProperties(3, newMovieProperties, 0, NULL, &myMovie);
        if (status != noErr || myMovie == NULL) {
            NSLog(@"Problem initializing theMovie"); // problem
            [self release];
            return nil;
        }

        // Create a new QTMovie with the Movie as its backing object
        sourceMovie = [QTMovie movieWithQuickTimeMovie:myMovie disposeWhenDone:NO error:&e];
        if (e) {
            NSLog(@"Could not initialize QTMovie from Movie.");
            [self release];
            return nil;
        }

        [sourceMovie stepForward];
        analyzer = [[MovieAnalyzer alloc] initWithColorString:"BGRA" andSourceSize:sourceSize];
    }
    return self;
}


-(NSImage*) supplyCalibrationImage {
    NSLog(@"%x", &sourceMovie);

    [sourceMovie stepForward];    // This fails!
    ....
}

Answer 1

[QTMovie movieWithQuickTimeMovie:disposeWhenDone:error:] is returning an autoreleased movie. If you want it to stick around past that one method, you need to retain it.