AVAsset在iOS中使用圖像覆蓋保存視頻廢墟視頻

Question

我試圖將圖像疊加和視頻合併到一個新的視頻文件中。這是我正在使用的代碼：

- (void)mergeVideoUrl:(NSURL *)videoURL andOverlayImage:(UIImage *)overlayImage 
{ 
    NSLog(@"%s", __PRETTY_FUNCTION__); 

    // Create an AVURLAsset 
    AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL:videoURL options:nil]; 
    AVMutableComposition* mixComposition = [AVMutableComposition composition]; 

    AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; 
    AVAssetTrack *clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) 
            ofTrack:clipVideoTrack 
            atTime:kCMTimeZero 
            error:nil]; 

    [compositionVideoTrack setPreferredTransform:[[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] preferredTransform]]; 

    CGSize videoSize = [clipVideoTrack naturalSize]; 

    // Get our image layer 
    CALayer *aLayer = [CALayer layer]; 
    aLayer.contents = (id)overlayImage.CGImage; 
    aLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height); 
    aLayer.opacity = 1.0; 

    // Sort the layer order 
    CALayer *parentLayer = [CALayer layer]; 
    CALayer *videoLayer = [CALayer layer]; 
    parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height); 
    videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height); 
    [parentLayer addSublayer:videoLayer]; 
    [parentLayer addSublayer:aLayer]; 

    // Create the composition and add the instructions to insert the layer 
    AVMutableVideoComposition* videoComp = [AVMutableVideoComposition videoComposition]; 
    videoComp.renderSize = videoSize; 
    videoComp.frameDuration = CMTimeMake(1, 30); 
    videoComp.animationTool = [AVVideoCompositionCoreAnimationTool  videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer]; 

    // Instruction 
    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; 
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mixComposition duration]); 
    AVAssetTrack *videoTrack = [[mixComposition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 
    AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack]; 
    instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction]; 
    videoComp.instructions = [NSArray arrayWithObject: instruction]; 

    // Export 
    AVAssetExportSession *assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality]; 
    assetExport.videoComposition = videoComp; 

    NSString* videoName = @"mynewwatermarkedvideo.mov"; 

    NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:videoName]; 
    NSURL *exportUrl = [NSURL fileURLWithPath:exportPath]; 

    if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) 
    { 
     [[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil]; 
    } 

    assetExport.outputFileType = AVFileTypeQuickTimeMovie; 
    assetExport.outputURL = exportUrl; 
    assetExport.shouldOptimizeForNetworkUse = YES; 

    [assetExport exportAsynchronouslyWithCompletionHandler:^(void) 
    { 
     //FINALIZATION CODE HERE 
     NSLog(@"DONE: %@", exportUrl); 
    }]; 
} 

問題是，它擰緊了視頻。任何想法爲什麼？ 我有一種感覺，視頻幀的大小可能與它或縱橫比有關，如果我設置了(2000,2000)的大小，它似乎工作正常，但有很多黑色邊緣。

EDIT ----- 看來，如果我設置CGSize videoSize到2/3例如比320x480或1280x1920然後它可以工作，但是最終的視頻右下方有一個黑條。爲什麼[clipVideoTrack naturalSize]報告的尺寸爲1080x1920，但是如果沒有使用1280x1920，它會被鎖定？我認爲這可能是一個轉換/作物問題？

EDIT2 ----- 更改AVAssetExportSessionAVAssetExportPresetLowQuality presetName之間，AVAssetExportPresetMediumQuality & AVAssetExportPresetHighestQuality導致不同尺寸的視頻。所以我認爲這在某種程度上壓倒了輸出視頻幀的大小。

Answer 1

CGSize videoSize = [clipVideoTrack naturalSize]; 

這使您可以記錄的尺寸，但你需要看着賽道的prefferedTransform找到記錄的方向。您可能會發現視頻寬度實際上是「高度」，具體取決於錄製過程中設備的保持方式。

我看你把它的組成，但你需要檢查它以正確的幀分配給您的CALayers