如何从静止图像 (png) 渲染固定长度的视频文件

Question

我正在尝试从静止图像 (png) 创建指定长度的视频。我的代码基于 How do I export UIImage as a movie

中给出的答案

我的代码创建了一个长度正确的视频，但图像确实出现到最后一帧。我希望在视频的整个持续时间内显示图像。（这些视频将成为无缝时间轴中的占位符。）

我的代码是：

- (NSURL*)exportImage:(NSImage*)image asMovieLength:(double)seconds {

    NSURL *outFile;
    AppDelegate *theApp;
    NSError *error=nil;
    AVAssetWriter *videoWriter;
    NSDictionary *videoSettings;
    AVAssetWriterInput* writerInput;
    CVPixelBufferRef buffer = NULL;
    AVAssetWriterInputPixelBufferAdaptor *adaptor;

    theApp = (AppDelegate*)[[NSApplication sharedApplication] delegate];

    outFile = [theApp getFilenameForFillerFile];

    videoWriter = [[AVAssetWriter alloc] initWithURL:outFile fileType:AVFileTypeMPEG4 error:&error];
    NSParameterAssert(videoWriter);

    videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:AVVideoCodecH264, AVVideoCodecKey,
                     [NSNumber numberWithInt:880], AVVideoWidthKey,
                     [NSNumber numberWithInt:880], AVVideoHeightKey,
                     nil];

    writerInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];

    adaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput
                                                                               sourcePixelBufferAttributes:nil];

    NSParameterAssert(writerInput);
    NSParameterAssert([videoWriter canAddInput:writerInput]);
    [videoWriter addInput:writerInput];

    // Start the writing session
    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:kCMTimeZero];


    if(writerInput.readyForMoreMediaData)
    {
        CMTime zeroTime = CMTimeMake(0, 600);
        CMTime frameTime = CMTimeMake(seconds*600, 600);
        buffer = [self pixelBufferFromImage:image];

        [adaptor appendPixelBuffer:buffer withPresentationTime:frameTime];

        [writerInput markAsFinished];

        [videoWriter finishWritingWithCompletionHandler:^{
            NSLog(@"Finished writing...checking completion status...");
            if (videoWriter.status != AVAssetWriterStatusFailed && videoWriter.status == AVAssetWriterStatusCompleted)
            {
                NSLog(@"Video writing succeeded.");

            } else
            {
                NSLog(@"Video writing failed: %@", videoWriter.error);
            }

        }];

        CVPixelBufferPoolRelease(adaptor.pixelBufferPool);

        NSLog (@"Done");
    }

    return outFile;
}

如何让图像从头开始显示并持续指定的时间？

Answer 1

我对代码进行了以下更改。

CMTime zeroTime = CMTimeMake(0, 600);
CMTime frameTime = CMTimeMake((seconds * 0.5) * 600, 600);

buffer = [self pixelBufferFromImage:image];

[adaptor appendPixelBuffer:buffer withPresentationTime:zeroTime];
[adaptor appendPixelBuffer:buffer withPresentationTime:frameTime];

如何从静止图像 (png) 渲染固定长度的视频文件

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