What would cause appendPixelBuffer to return false?

Question

My code is simple, I'm taking a image and putting it as the title slide of a video that's frames were extracted. But for some reason the appendPixelBuffer keeps returning false. All frames are set to the exact height/width of 1200 by 1200.

The error being returned from the AVAssetWritter is:

Error Domain=AVFoundationErrorDomain Code=-11823 "Cannot Save" UserInfo=0x10c5c4b40 {NSUnderlyingError=0x113716cf0 "The operation couldn’t be completed. (OSStatus error -12412.)", NSLocalizedRecoverySuggestion=Try saving again., NSLocalizedDescription=Cannot Save}

My code is below:

NSError *error = nil;

AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:
                              [NSURL fileURLWithPath:[VideoHandler movieLocation]] fileType:AVFileTypeQuickTimeMovie
                                                          error:&error];
NSParameterAssert(videoWriter);

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt:1200], AVVideoWidthKey,
                               [NSNumber numberWithInt:1200], AVVideoHeightKey,
                               nil];

AVAssetWriterInput* videoWriterInput = [AVAssetWriterInput
                                        assetWriterInputWithMediaType:AVMediaTypeVideo
                                        outputSettings:videoSettings];


AVAssetWriterInputPixelBufferAdaptor *adaptor = [AVAssetWriterInputPixelBufferAdaptor
                                                 assetWriterInputPixelBufferAdaptorWithAssetWriterInput:videoWriterInput
                                                 sourcePixelBufferAttributes:nil];

NSParameterAssert(videoWriterInput);
NSParameterAssert([videoWriter canAddInput:videoWriterInput]);
videoWriterInput.expectsMediaDataInRealTime = YES;
[videoWriter addInput:videoWriterInput];

//Start a session:
[videoWriter startWriting];
[videoWriter startSessionAtSourceTime:kCMTimeZero];

CVPixelBufferRef buffer = NULL;

int frameCount = 0;
for (int i = (int)assets.count; i > 0; i --) {
    UIImage *img = [SelectedImage getImage];
    buffer = [self pixelBufferFromCGImage:[img CGImage] andSize:[img size]];

    BOOL append_ok = NO;
    int j = 0;
    while (!append_ok && j < 30)
    {
        if (adaptor.assetWriterInput.readyForMoreMediaData)
        {
            printf("appending %d attemp %d\n", frameCount, j);

            //int fps = [[imageDurations objectAtIndex:frameCount] intValue];
            CMTime frameTime = CMTimeMake(frameCount, (int32_t)15 / [imageDurations count]);
            append_ok = [adaptor appendPixelBuffer:buffer withPresentationTime:frameTime];

            if(buffer)
                CVBufferRelease(buffer);
            [NSThread sleepForTimeInterval:0.05];
        }
        else
        {
            printf("adaptor not ready %d, %d\n", frameCount, j);
            NSDate *maxDate = [NSDate dateWithTimeIntervalSinceNow:0.1];
            [[NSRunLoop currentRunLoop] runUntilDate:maxDate];
        }
        j++;
    }
    if (!append_ok) {
        printf("error appending image %d times %d\n", frameCount, j);
    }

    frameCount++;
}

//Finish the session:
[videoWriterInput markAsFinished];
[videoWriter finishWriting];

Answer 1

Okay, after doing some file searching on my iPhone, I found that the directory that I was trying to store the video at already existed. The easiest fix is to store all of this into a temp directory and to clear it on launch and close in the event of a crash.