项目中有一个视频自定义区域裁剪的需求，即：用户选取要裁剪的区域去剪辑，区域之外的视频画面会被丢弃。实现效果如下：
IMG_5337.PNG
如图所示，视频页面上是一个拖拽框，添加手势，使之可以自由调节大小，也可以按比例调节大小，按照选取的范围去裁剪视频。好了，UI层面上的东西不再多说。裁剪视频需要用到可能很多开发者都比较陌生的两个类AVMutableVideoCompositionInstruction和AVMutableVideoCompositionLayerInstruction。
AVMutableVideoCompositionInstruction是视频轨道中的一个视频，可以缩放、旋转等。AVMutableVideoCompositionLayerInstruction是一个轨道视频，包含了这个轨道上所有的视频素材。还是直接上代码(我知道你们也不想看我啰哩啰嗦)：
BOOL Assetvertical =NO;
//创建AVAsset实例 AVAsset包含了video的所有信息
NSDictionary *option = [NSDictionary dictionaryWithObject:@(YES) forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
AVAsset *videoAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:videoPath] options:option];
//创建AVMutableComposition实例.
AVMutableComposition *mixComposition = [AVMutableComposition composition];
//开始时间
CMTime startTime =CMTimeMakeWithSeconds(0,videoAsset.duration.timescale);
//结束时间
CMTime endTime =CMTimeMakeWithSeconds(videoAsset.duration.value/videoAsset.duration.timescale,videoAsset.duration.timescale);
// CMTimeRange timeRange =CMTimeRangeMake(startTime, endTime);
NSLog(@"视频_____%lld____%d",videoAsset.duration.value,videoAsset.duration.timescale);
//3 视频通道 工程文件中的轨道，有音频轨、视频轨等，里面可以插入各种对应的素材
AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
NSError *error;
//把视频轨道数据加入到可变轨道中 这部分可以做视频裁剪TimeRange
[videoTrack insertTimeRange:CMTimeRangeMake(startTime, endTime)
ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] lastObject]
atTime:kCMTimeZero error:&error];
//有声音
if ([[videoAsset tracksWithMediaType:AVMediaTypeAudio] count] > 0){
//声音采集
AVURLAsset * audioAsset = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:videoPath] options:option];
//音频通道
AVMutableCompositionTrack * audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
//音频采集通道
AVAssetTrack * audioAssetTrack = [[audioAsset tracksWithMediaType:AVMediaTypeAudio] lastObject];
[audioTrack insertTimeRange:CMTimeRangeMake(startTime,endTime) ofTrack:audioAssetTrack atTime:kCMTimeZero error:nil];
}
//3.1 AVMutableVideoCompositionInstruction 视频轨道中的一个视频，可以缩放、旋转等
AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = CMTimeRangeMake(startTime,endTime);
// 3.2 AVMutableVideoCompositionLayerInstruction 一个视频轨道，包含了这个轨道上的所有视频素材
AVMutableVideoCompositionLayerInstruction *videolayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
AVAssetTrack *videoAssetTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] lastObject];
UIImageOrientation videoAssetOrientation_ = UIImageOrientationUp;
//拍摄的时候视频是否是竖屏拍的
BOOL isVideoAssetvertical = NO;
CGAffineTransform videoTransform = videoAssetTrack.preferredTransform;
if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) {
isVideoAssetvertical = YES;
videoAssetOrientation_ = UIImageOrientationUp;//正着拍
}
if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) {
isVideoAssetvertical = YES;
videoAssetOrientation_ = UIImageOrientationDown;//倒着拍
}
if (videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0) {
isVideoAssetvertical = NO;
videoAssetOrientation_ = UIImageOrientationLeft;//左边拍
}
if (videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0) {
isVideoAssetvertical = NO;
videoAssetOrientation_ = UIImageOrientationRight;//右边拍
}
float scaleX = 1.0,scaleY = 1.0,scale = 1.0;
CGSize originVideoSize;
if (isVideoAssetvertical || Assetvertical) {
originVideoSize = CGSizeMake([[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize].height, [[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize].width);
}
else{
originVideoSize = CGSizeMake([[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize].width, [[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] naturalSize].height);
}
float x = videoPoint.x;
float y = videoPoint.y;
if (shouldScale) {
scaleX = videoSize.width/originVideoSize.width;
scaleY = videoSize.height/originVideoSize.height;
scale = MAX(scaleX, scaleY);
if (scaleX>scaleY) {
NSLog(@"竖屏");
}
else{
NSLog(@"横屏");
}
}
else{
scaleX = 1.0;
scaleY = 1.0;
scale = 1.0;
}
if (Assetvertical) {
CGAffineTransform trans = CGAffineTransformMake(videoAssetTrack.preferredTransform.a*scale, videoAssetTrack.preferredTransform.b*scale, videoAssetTrack.preferredTransform.c*scale, videoAssetTrack.preferredTransform.d*scale, videoAssetTrack.preferredTransform.tx*scale-x+720, videoAssetTrack.preferredTransform.ty*scale-y);
// [videolayerInstruction setTransform:trans atTime:kCMTimeZero];
CGAffineTransform trans2 = CGAffineTransformRotate(trans, M_PI_2);
[videolayerInstruction setTransform:trans2 atTime:kCMTimeZero];
}
else{
CGAffineTransform trans = CGAffineTransformMake(videoAssetTrack.preferredTransform.a*scale, videoAssetTrack.preferredTransform.b*scale, videoAssetTrack.preferredTransform.c*scale, videoAssetTrack.preferredTransform.d*scale, videoAssetTrack.preferredTransform.tx*scale-x, videoAssetTrack.preferredTransform.ty*scale-y);
[videolayerInstruction setTransform:trans atTime:kCMTimeZero];
}
//裁剪区域
mainInstruction.layerInstructions = [NSArray arrayWithObjects:videolayerInstruction,nil];
//AVMutableVideoComposition：管理所有视频轨道，可以决定最终视频的尺寸，裁剪需要在这里进行
AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];
CGSize naturalSize = originVideoSize;
int64_t renderWidth = 0, renderHeight = 0;
if (videoSize.height ==0.0 || videoSize.width == 0.0) {
renderWidth = naturalSize.width;
renderHeight = naturalSize.height;
}
else{
renderWidth = ceil(videoSize.width);
renderHeight = ceil(videoSize.height);
}
mainCompositionInst.renderSize = CGSizeMake(renderWidth,renderHeight);
mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction];
mainCompositionInst.frameDuration = CMTimeMake(1,30);
经过以上这一步，我们就得到了一个AVMutableVideoComposition对象，这正是我们所需要的，剩下的就是使用 AVAssetExportSession导出视频就行了，如下：
//视频文件输出
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
presetName:presetName];
exporter.outputURL=compressionFileURL;
exporter.outputFileType = outputFileType;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mainCompositionInst;
[exporter exportAsynchronouslyWithCompletionHandler:^{
dispatch_async(dispatch_get_main_queue(), ^{
switch (exporter.status) {
case AVAssetExportSessionStatusFailed:{
if (completeBlock) {
completeBlock(exporter.error,compressionFileURL);
}
break;
}
case AVAssetExportSessionStatusCancelled:{
NSLog(@"Export Status: Cancell");
break;
}
case AVAssetExportSessionStatusCompleted: {
if (completeBlock) {
completeBlock(nil,compressionFileURL);
}
break;
}
case AVAssetExportSessionStatusUnknown: {
NSLog(@"Export Status: Unknown");
break;
}
case AVAssetExportSessionStatusExporting : {
NSLog(@"Export Status: Exporting");
break;
}
case AVAssetExportSessionStatusWaiting: {
NSLog(@"Export Status: Wating");
break;
}
};
});
}];
注：我们还可以同时设置exporter.timeRange,这样在裁剪视频区域的同时还可以剪辑视频时间，不明白的同学见上一遍文章短视频从无到有 (十)视频自定义时间剪辑。
有什么问题，欢迎留言讨论。
