我正在尝试旋转 avplayer，但是当我旋转它时，它从头开始旋转，我想在播放时随时旋转，它应该从那里旋转。我正在使用苹果文档，这段代码取自那里.这是我的代码。`
-(void)performWithAsset:(AVAsset*)asset
{
AVMutableVideoCompositionInstruction *instruction = nil;
AVMutableVideoCompositionLayerInstruction *layerInstruction = nil;
CGAffineTransform t1;
CGAffineTransform t2;
AVAssetTrack *assetVideoTrack = nil;
AVAssetTrack *assetAudioTrack = nil;
// Check if the asset contains video and audio tracks
if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) {
assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];
}
if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] != 0) {
assetAudioTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];
}
CMTime insertionPoint = kCMTimeInvalid;
NSError *error = nil;
// Step 1
// Create a composition with the given asset and insert audio and video tracks into it from the asset
if (!self.mutableComposition) {
// Check whether a composition has already been created, i.e, some other tool has already been applied
// Create a new composition
self.mutableComposition = [AVMutableComposition composition];
// Insert the video and audio tracks from AVAsset
if (assetVideoTrack != nil) {
AVMutableCompositionTrack *compositionVideoTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:assetVideoTrack atTime:insertionPoint error:&error];
}
if (assetAudioTrack != nil) {
AVMutableCompositionTrack *compositionAudioTrack = [self.mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:assetAudioTrack atTime:insertionPoint error:&error];
}
}
// Step 2
// Translate the composition to compensate the movement caused by rotation (since rotation would cause it to move out of frame)
t1 = CGAffineTransformMakeTranslation(assetVideoTrack.naturalSize.height, 0.0);
// Rotate transformation
t2 = CGAffineTransformRotate(t1, degreesToRadians(90.0));
// Step 3
// Set the appropriate render sizes and rotational transforms
if (!self.mutableVideoComposition) {
// Create a new video composition
self.mutableVideoComposition = [AVMutableVideoComposition videoComposition];
self.mutableVideoComposition.renderSize = CGSizeMake(assetVideoTrack.naturalSize.height,assetVideoTrack.naturalSize.width);
self.mutableVideoComposition.frameDuration = CMTimeMake(1, 30);
// The rotate transform is set on a layer instruction
instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [self.mutableComposition duration]);
layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:(self.mutableComposition.tracks)[0]];
[layerInstruction setTransform:t2 atTime:kCMTimeZero];
} else {
self.mutableVideoComposition.renderSize = CGSizeMake(self.mutableVideoComposition.renderSize.height, self.mutableVideoComposition.renderSize.width);
// Extract the existing layer instruction on the mutableVideoComposition
instruction = (self.mutableVideoComposition.instructions)[0];
layerInstruction = (instruction.layerInstructions)[0];
// Check if a transform already exists on this layer instruction, this is done to add the current transform on top of previous edits
CGAffineTransform existingTransform;
if (![layerInstruction getTransformRampForTime:[self.mutableComposition duration] startTransform:&existingTransform endTransform:NULL timeRange:NULL]) {
[layerInstruction setTransform:t2 atTime:kCMTimeZero];
} else {
// Note: the point of origin for rotation is the upper left corner of the composition, t3 is to compensate for origin
CGAffineTransform t3 = CGAffineTransformMakeTranslation(-1*assetVideoTrack.naturalSize.height/2, 0.0);
CGAffineTransform newTransform = CGAffineTransformConcat(existingTransform, CGAffineTransformConcat(t2, t3));
[layerInstruction setTransform:newTransform atTime:kCMTimeZero];
}
}
// Step 4
enter code here
// Add the transform instructions to the video composition
instruction.layerInstructions = @[layerInstruction];
self.mutableVideoComposition.instructions = @[instruction];
// Step 5
// Notify AVSEViewController about rotation operation completion
[[NSNotificationCenter defaultCenter] postNotificationName:AVSEEditCommandCompletionNotification object:self];
}