使用AVFoundation更改视频帧大小

Question

我试图将视频帧大小更改为正方形，即100 x 100。下面是代码:

- (void) changeSize :(NSURL *) url
{
//Create audio/video Settings
NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt: 100], AVVideoWidthKey, 
                               [NSNumber numberWithInt:100], AVVideoHeightKey, 
                               nil];
NSDictionary * audioSettings = [NSDictionary dictionaryWithObjectsAndKeys: 
                               [NSNumber numberWithFloat: 44100.0], AVSampleRateKey, 
                               [NSNumber numberWithInt: 2], AVNumberOfChannelsKey, 
                               [NSNumber numberWithInt: kAudioFormatAppleLossless], AVFormatIDKey, 
                               [NSData data], AVChannelLayoutKey, nil];

//Read Asset 
AVURLAsset *myAsset = [AVURLAsset URLAssetWithURL:url options:nil];
NSArray *videoTracks = [myAsset tracksWithMediaType:AVMediaTypeVideo];
AVAssetTrack *audioTrack = [[myAsset tracksWithMediaType:AVMediaTypeAudio]objectAtIndex:0];

AVAssetReader *assetReader = [[AVAssetReader alloc]initWithAsset:myAsset error:nil];
AVAssetReaderOutput *videoOutput = [AVAssetReaderVideoCompositionOutput assetReaderVideoCompositionOutputWithVideoTracks:videoTracks videoSettings:nil];
AVAssetReaderOutput *audioOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:nil];
[assetReader addOutput:videoOutput];
[assetReader addOutput:audioOutput];

//Create writer and set its properties
AVAssetWriterInput* writerInputVideo = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
                                                                           outputSettings:videoSettings] retain];
AVAssetWriterInput* writerInputAudio = [[AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio
                                                                           outputSettings:nil] retain];

NSError *error = nil;
AVAssetWriter *writer = [[AVAssetWriter alloc]initWithURL:[NSURL fileURLWithPath:fullPath] fileType:AVFileTypeQuickTimeMovie error:&error];
[writer addInput:writerInputVideo];
[writer addInput:writerInputAudio];

//start reading/writting
[writer startWriting];
[assetReader startReading];
}

现在的问题是，当它到达[assetreaderstartreading]，它抛出一个异常说"AVAssetReaderVideoCompositionOutput。videoComposition需要设置为".

谁能给我指路?

TIA

Answer 1

我自己做的。查看一下:

- (void) resizeVideo:(NSURL *)videoPath outputPath:(NSURL *)outputPath
{
NSURL *fullPath = outputPath;
NSURL *path = videoPath;

NSLog(@"Write Started");
NSError *error = nil;
AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:fullPath fileType:AVFileTypeQuickTimeMovie error:&error];    
NSParameterAssert(videoWriter);
NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt:100], AVVideoWidthKey,
                               [NSNumber numberWithInt:100], AVVideoHeightKey,
                               nil];
AVAssetWriterInput* videoWriterInput = [[AVAssetWriterInput
                                         assetWriterInputWithMediaType:AVMediaTypeVideo
                                         outputSettings:videoSettings] retain];
NSParameterAssert(videoWriterInput);
NSParameterAssert([videoWriter canAddInput:videoWriterInput]);
videoWriterInput.expectsMediaDataInRealTime = NO;
[videoWriter addInput:videoWriterInput];


AVAsset *avAsset = [[AVURLAsset alloc] initWithURL:path options:nil];
NSError *aerror = nil;
AVAssetReader *reader = [[AVAssetReader alloc] initWithAsset:avAsset error:&aerror];

AVAssetTrack *videoTrack = [[avAsset tracksWithMediaType:AVMediaTypeVideo]objectAtIndex:0];
NSDictionary *videoOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey];
AVAssetReaderTrackOutput *asset_reader_output = [[AVAssetReaderTrackOutput alloc] initWithTrack:videoTrack outputSettings:videoOptions];    
[reader addOutput:asset_reader_output];

[videoWriter startWriting];
[videoWriter startSessionAtSourceTime:kCMTimeZero];
[reader startReading];
CMSampleBufferRef buffer;

while ( [reader status]==AVAssetReaderStatusReading )
{
    if(![videoWriterInput isReadyForMoreMediaData])
        continue;
    buffer = [asset_reader_output copyNextSampleBuffer];

    NSLog(@"READING");
    if(buffer)
        [videoWriterInput appendSampleBuffer:buffer];
    NSLog(@"WRITTING...");

}

//Finish the session:
[videoWriterInput markAsFinished];  
[videoWriter finishWriting];
NSLog(@"Write Ended");
}