我使用下面的代码在视频上添加图像叠加，然后将新生成的视频导出到文档目录。但奇怪的是，视频被旋转了 90 度。
- (void)buildTransitionComposition:(AVMutableComposition *)composition andVideoComposition:(AVMutableVideoComposition *)videoComposition
{
CMTime nextClipStartTime = kCMTimeZero;
NSInteger i;
// Make transitionDuration no greater than half the shortest clip duration.
CMTime transitionDuration = self.transitionDuration;
for (i = 0; i < [_clips count]; i++ ) {
NSValue *clipTimeRange = [_clipTimeRanges objectAtIndex:i];
if (clipTimeRange) {
CMTime halfClipDuration = [clipTimeRange CMTimeRangeValue].duration;
halfClipDuration.timescale *= 2; // You can halve a rational by doubling its denominator.
transitionDuration = CMTimeMinimum(transitionDuration, halfClipDuration);
}
}
// Add two video tracks and two audio tracks.
AVMutableCompositionTrack *compositionVideoTracks[2];
AVMutableCompositionTrack *compositionAudioTracks[2];
compositionVideoTracks[0] = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
compositionVideoTracks[1] = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
compositionAudioTracks[0] = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
compositionAudioTracks[1] = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
CMTimeRange *passThroughTimeRanges = alloca(sizeof(CMTimeRange) * [_clips count]);
CMTimeRange *transitionTimeRanges = alloca(sizeof(CMTimeRange) * [_clips count]);
// Place clips into alternating video & audio tracks in composition, overlapped by transitionDuration.
for (i = 0; i < [_clips count]; i++ ) {
NSInteger alternatingIndex = i % 2; // alternating targets: 0, 1, 0, 1, ...
AVURLAsset *asset = [_clips objectAtIndex:i];
NSValue *clipTimeRange = [_clipTimeRanges objectAtIndex:i];
CMTimeRange timeRangeInAsset;
if (clipTimeRange)
timeRangeInAsset = [clipTimeRange CMTimeRangeValue];
else
timeRangeInAsset = CMTimeRangeMake(kCMTimeZero, [asset duration]);
AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[compositionVideoTracks[alternatingIndex] insertTimeRange:timeRangeInAsset ofTrack:clipVideoTrack atTime:nextClipStartTime error:nil];
/*
CGAffineTransform t = clipVideoTrack.preferredTransform;
NSLog(@"Transform1 : %@",t);
*/
AVAssetTrack *clipAudioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
[compositionAudioTracks[alternatingIndex] insertTimeRange:timeRangeInAsset ofTrack:clipAudioTrack atTime:nextClipStartTime error:nil];
// Remember the time range in which this clip should pass through.
// Every clip after the first begins with a transition.
// Every clip before the last ends with a transition.
// Exclude those transitions from the pass through time ranges.
passThroughTimeRanges[i] = CMTimeRangeMake(nextClipStartTime, timeRangeInAsset.duration);
if (i > 0) {
passThroughTimeRanges[i].start = CMTimeAdd(passThroughTimeRanges[i].start, transitionDuration);
passThroughTimeRanges[i].duration = CMTimeSubtract(passThroughTimeRanges[i].duration, transitionDuration);
}
if (i+1 < [_clips count]) {
passThroughTimeRanges[i].duration = CMTimeSubtract(passThroughTimeRanges[i].duration, transitionDuration);
}
// The end of this clip will overlap the start of the next by transitionDuration.
// (Note: this arithmetic falls apart if timeRangeInAsset.duration < 2 * transitionDuration.)
nextClipStartTime = CMTimeAdd(nextClipStartTime, timeRangeInAsset.duration);
nextClipStartTime = CMTimeSubtract(nextClipStartTime, transitionDuration);
// Remember the time range for the transition to the next item.
transitionTimeRanges[i] = CMTimeRangeMake(nextClipStartTime, transitionDuration);
}
// Set up the video composition if we are to perform crossfade or push transitions between clips.
NSMutableArray *instructions = [NSMutableArray array];
// Cycle between "pass through A", "transition from A to B", "pass through B", "transition from B to A".
for (i = 0; i < [_clips count]; i++ ) {
NSInteger alternatingIndex = i % 2; // alternating targets
// Pass through clip i.
AVMutableVideoCompositionInstruction *passThroughInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
passThroughInstruction.timeRange = passThroughTimeRanges[i];
AVMutableVideoCompositionLayerInstruction *passThroughLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTracks[alternatingIndex]];
/*
CGAffineTransform rotationTransform = CGAffineTransformMakeRotation(M_PI_2);
CGAffineTransform rotateTranslate = CGAffineTransformTranslate(rotationTransform,320,0);
[passThroughLayer setTransform:rotateTranslate atTime:kCMTimeZero];
*/
passThroughInstruction.layerInstructions = [NSArray arrayWithObject:passThroughLayer];
[instructions addObject:passThroughInstruction];
if (i+1 < [_clips count]) {
// Add transition from clip i to clip i+1.
AVMutableVideoCompositionInstruction *transitionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
transitionInstruction.timeRange = transitionTimeRanges[i];
AVMutableVideoCompositionLayerInstruction *fromLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTracks[alternatingIndex]];
AVMutableVideoCompositionLayerInstruction *toLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTracks[1-alternatingIndex]];
if (self.transitionType == SimpleEditorTransitionTypeCrossFade) {
// Fade out the fromLayer by setting a ramp from 1.0 to 0.0.
[fromLayer setOpacityRampFromStartOpacity:1.0 toEndOpacity:0.0 timeRange:transitionTimeRanges[i]];
}
else if (self.transitionType == SimpleEditorTransitionTypePush) {
// Set a transform ramp on fromLayer from identity to all the way left of the screen.
[fromLayer setTransformRampFromStartTransform:CGAffineTransformIdentity toEndTransform:CGAffineTransformMakeTranslation(-composition.naturalSize.width, 0.0) timeRange:transitionTimeRanges[i]];
// Set a transform ramp on toLayer from all the way right of the screen to identity.
[toLayer setTransformRampFromStartTransform:CGAffineTransformMakeTranslation(+composition.naturalSize.width, 0.0) toEndTransform:CGAffineTransformIdentity timeRange:transitionTimeRanges[i]];
}
transitionInstruction.layerInstructions = [NSArray arrayWithObjects:fromLayer, toLayer, nil];
[instructions addObject:transitionInstruction];
}
}
videoComposition.instructions = instructions;
}
请帮助，因为我无法以正确的模式导出肖像视频。任何帮助表示赞赏。谢谢你。