最近项目要搞视频编辑相关的东西。于是就有了这些文章。

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视频相关入门
『ios』视频编辑入门 【视频背景音乐合成】
『ios』视频编辑入门【添加水印】
『ios』视频编辑入门【画中画实现】改变视频尺寸
视频编辑主要用的AVFoundation。
涉及到的AVFoundation的类。
AVAsset：素材库里的素材；
AVAssetTrack：素材的轨道；
AVMutableComposition ：一个用来合成视频的工程文件；
AVMutableCompositionTrack ：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；

AVMutableVideoComposition：用来生成video的组合指令，包含多段instruction。可以决定最终视频的尺寸，裁剪需要在这里进行；
AVMutableVideoCompositionInstruction：一个指令，决定一个timeRange内每个轨道的状态，包含多个layerInstruction；
AVMutableVideoCompositionLayerInstruction 可以用来设置 video track 的图形变换、图形渐变、透明度、透明度渐变等等。一个 video composition instruction 的 layerInstructions 属性中所存储的 layer instructions 的顺序决定了 tracks 中的视频帧是如何被放置和组合的；
AVAssetExportSession：导出视频需要用到的类

视频背景音乐合成

1.拿到两个视频跟一个背景音乐的路径

  NSURL *videoPath1 = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"1" ofType:@"mp4"]];
    NSURL *videoPath2 = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"2" ofType:@"mp4"]];
    NSURL *music = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"music" ofType:@"mp3"]];

   AVAsset *firstAsset = [AVAsset assetWithURL:firstVideoPath];
    AVAsset *secondAsset = [AVAsset assetWithURL:secondVideo];
    AVAsset *musciAsset = [AVAsset assetWithURL:musicPath];

2.创建合成文件

AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];

3.创建视频轨道轨道并合成

    AVMutableCompositionTrack *firstTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
                                                                        preferredTrackID:kCMPersistentTrackID_Invalid];
    [firstTrack insertTimeRange:CMTimeRangeFromTimeToTime(kCMTimeZero, firstAsset.duration)
                        ofTrack:[[firstAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil];
    [firstTrack insertTimeRange:CMTimeRangeFromTimeToTime(kCMTimeZero, secondAsset.duration)
                        ofTrack:[[secondAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:firstAsset.duration error:nil];

4.创建音频轨道并合成

   if (musciAsset!=nil){
        //把音频  Adds an empty track to a mutable composition
        AVMutableCompositionTrack *AudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                                preferredTrackID:kCMPersistentTrackID_Invalid];
        [AudioTrack insertTimeRange:CMTimeRangeFromTimeToTime(kCMTimeZero, CMTimeAdd(firstAsset.duration, secondAsset.duration))
                                ofTrack:[[musciAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] atTime:kCMTimeZero error:nil];
    }

5.调整声音

    AVMutableAudioMix *videoAudioMixTools = [AVMutableAudioMix audioMix];
    if (musciAsset) {
        //调节音量
        //获取音频轨道
        AVMutableAudioMixInputParameters *firstAudioParam = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:AudioTrack];
        //设置音轨音量,可以设置渐变,设置为1.0就是全音量
        [firstAudioParam setVolumeRampFromStartVolume:1.0 toEndVolume:1.0 timeRange:CMTimeRangeMake(kCMTimeZero, CMTimeAdd(firstAsset.duration, secondAsset.duration))];
        [firstAudioParam setTrackID:AudioTrack.trackID];
        videoAudioMixTools.inputParameters = [NSArray arrayWithObject:firstAudioParam];
    }

6.获取视频存储路径

   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:
                             [NSString stringWithFormat:@"mergeVideo-%d.mp4",arc4random() % 1000]];
    NSURL *url = [NSURL fileURLWithPath:myPathDocs];

7.导出视频 存到相册

    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
                                                                      presetName:AVAssetExportPresetHighestQuality];
   exporter.outputURL=url;//导出的路径
    exporter.outputFileType = AVFileTypeQuickTimeMovie;
    exporter.audioMix = videoAudioMixTools;//声音
    exporter.shouldOptimizeForNetworkUse = YES;
    [exporter exportAsynchronouslyWithCompletionHandler:^{
        dispatch_async(dispatch_get_main_queue(), ^{
            [self exportDidFinish:exporter];
        });
    }];

- (void)exportDidFinish:(AVAssetExportSession*)session {
    if (session.status == AVAssetExportSessionStatusCompleted) {
        NSURL *outputURL = session.outputURL;
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            [SVProgressHUD dismiss];
            __block PHObjectPlaceholder *placeholder;
            if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(outputURL.path)) {
                NSError *error;
                [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
                    PHAssetChangeRequest* createAssetRequest = [PHAssetChangeRequest creationRequestForAssetFromVideoAtFileURL:outputURL];
                    placeholder = [createAssetRequest placeholderForCreatedAsset];
                } error:&error];
                if (error) {
                    [SVProgressHUD showErrorWithStatus:[NSString stringWithFormat:@"%@",error]];
                }
                else{
                    [SVProgressHUD showSuccessWithStatus:@"视频已经保存到相册"];
                }
            }else {
                [SVProgressHUD showErrorWithStatus:NSLocalizedString(@"视频保存相册失败，请设置软件读取相册权限", nil)];
            }
        });
    }
}

后面还会继续研究别的功能。。。