ios 中的视频录制问题

Question

我正在开发一个视频制作应用程序。
因为我需要在第一个视图中录制视频，然后在第二个视图中显示。
为了录制视频，我遵循了 this 教程。因为我根据需要在 didFinishRecordingToOutputFileAtURL 方法中做了一些更改。

这是我更新的方法。

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error
{
    NSLog(@"didFinishRecordingToOutputFileAtURL - enter");

    BOOL RecordedSuccessfully = YES;
    if ([error code] != noErr)
    {
        // A problem occurred: Find out if the recording was successful.
        id value = [[error userInfo] objectForKey:AVErrorRecordingSuccessfullyFinishedKey];
        if (value)
        {
            RecordedSuccessfully = [value boolValue];
        }
    }
    else {
        NSLog(@"didFinishRecordingToOutputFileAtURL error:%@",error);
    }
    if (RecordedSuccessfully)
    {
        //----- RECORDED SUCESSFULLY -----
        NSLog(@"didFinishRecordingToOutputFileAtURL - success");
        ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
        if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:outputFileURL])
        {
            AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];
            AVMutableCompositionTrack *track = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

            AVAsset *asset = [AVAsset assetWithURL:outputFileURL];

            [track insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:CMTimeMake(0, 1) error:nil];

            NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
            NSString *documentsDirectory = [paths objectAtIndex:0];
            NSString *myPathDocs =  [documentsDirectory stringByAppendingPathComponent:
                                     [NSString stringWithFormat:@"%@%d.mov",NSBundle.mainBundle.infoDictionary[@"CFBundleExecutable"],++videoCounter]];
            [[NSFileManager defaultManager] removeItemAtPath:myPathDocs error:nil];

            NSURL *url = [NSURL fileURLWithPath:myPathDocs];

            AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
            instruction.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);

            AVMutableVideoCompositionLayerInstruction *layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:track];
            AVAssetTrack *videoAssetTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
            UIImageOrientation videoAssetOrientation_  = UIImageOrientationUp;
            BOOL isVideoAssetPortrait_  = NO;
            CGAffineTransform videoTransform = videoAssetTrack.preferredTransform;

            if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) {
                videoAssetOrientation_ = UIImageOrientationRight;
                isVideoAssetPortrait_ = YES;
                if ([[[NSUserDefaults standardUserDefaults] stringForKey:@"orientation"] isEqualToString:@"landscape"]) {
                    videoAssetOrientation_ =  UIImageOrientationUp;
                }
            }
            if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) {
                videoAssetOrientation_ =  UIImageOrientationLeft;
                isVideoAssetPortrait_ = YES;
            }
            if (videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0) {
                videoAssetOrientation_ =  UIImageOrientationUp;
            }
            if (videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0) {
                videoAssetOrientation_ = UIImageOrientationDown;
            }

            CGSize naturalSize;
            if(isVideoAssetPortrait_){
                naturalSize = CGSizeMake(videoAssetTrack.naturalSize.height, videoAssetTrack.naturalSize.width);
            } else {
                naturalSize = videoAssetTrack.naturalSize;
            }

            float renderWidth, renderHeight;
            if (![self.ratioLabel.text isEqualToString:@"16:9"]) {
                renderWidth = naturalSize.width;
                renderHeight = naturalSize.width;
                NSLog(@"Video:: width=%f height=%f",naturalSize.width,naturalSize.height);
            }
            else {
                renderWidth = naturalSize.width;
                renderHeight = naturalSize.height;
                NSLog(@"Video:: width=%f height=%f",naturalSize.width,naturalSize.height);
            }
            if (![self.ratioLabel.text isEqualToString:@"16:9"])
            {
                CGAffineTransform t1 = CGAffineTransformMakeTranslation(videoAssetTrack.naturalSize.height, -(videoAssetTrack.naturalSize.width - videoAssetTrack.naturalSize.height) /2);
                CGAffineTransform t2 = CGAffineTransformRotate(t1, M_PI_2);
                [layerInstruction setTransform:t2 atTime:kCMTimeZero];
            }
            else
            {
                CGAffineTransform t2 = CGAffineTransformMakeRotation( M_PI_2);
                [layerInstruction setTransform:t2 atTime:kCMTimeZero];
            }

            AVCaptureDevicePosition position = [[VideoInputDevice device] position];
            if (position == AVCaptureDevicePositionFront)
            {
                /* For front camera only */
                CGAffineTransform t = CGAffineTransformMakeScale(-1.0f, 1.0f);
                t = CGAffineTransformTranslate(t, -videoAssetTrack.naturalSize.width, 0);
                t = CGAffineTransformRotate(t, (DEGREES_TO_RADIANS(90.0)));
                t = CGAffineTransformTranslate(t, 0.0f, -videoAssetTrack.naturalSize.width);
                [layerInstruction setTransform:t atTime:kCMTimeZero];
                /* For front camera only */
            }

            [layerInstruction setOpacity:0.0 atTime:asset.duration];

            instruction.layerInstructions = [NSArray arrayWithObjects:layerInstruction,nil];

            AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];


            mainCompositionInst.renderSize = CGSizeMake(renderWidth, renderHeight);
            mainCompositionInst.instructions = [NSArray arrayWithObject:instruction];
            mainCompositionInst.frameDuration = CMTimeMake(1, 30);

            AVAssetExportSession *exporter;
            exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPreset1280x720];
            exporter.videoComposition = mainCompositionInst;
            exporter.outputURL=url;
            exporter.outputFileType = AVFileTypeQuickTimeMovie;
            exporter.shouldOptimizeForNetworkUse = YES;

            [exporter exportAsynchronouslyWithCompletionHandler:^{
                dispatch_async(dispatch_get_main_queue(), ^{
                    self.doneButton.userInteractionEnabled = YES;
                    if(videoAddr==nil)
                    {
                        videoAddr = [[NSMutableArray alloc] init];
                    }
                    [videoAddr addObject:exporter.outputURL];
                    [[PreviewLayer connection] setEnabled:YES];
                    AVAsset *asset = [AVAsset assetWithURL:exporter.outputURL];
                    NSLog(@"remaining seconds before:%f",lastSecond);
                    double assetDuration = CMTimeGetSeconds(asset.duration);
                    if (assetDuration>3.0)
                        assetDuration = 3.0;
                    lastSecond = lastSecond- assetDuration;
                    NSLog(@"remaining seconds after:%f",lastSecond);
                    self.secondsLabel.text = [NSString stringWithFormat:@"%0.1fs",lastSecond];
                    self.secondsLabel.hidden = NO;
                    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:videoAddr];

                    [[NSUserDefaults standardUserDefaults] setObject:data forKey:@"videoAddr"];
                    [[NSUserDefaults standardUserDefaults] synchronize];
                    videoURL = outputFileURL;
                    flagAutorotate = NO;
                    self.cancelButton.hidden = self.doneButton.hidden = NO;
                    imgCancel.hidden = imgDone.hidden = NO;
                    if ([[NSUserDefaults standardUserDefaults] boolForKey:@"Vibration"])
                        AudioServicesPlayAlertSound(kSystemSoundID_Vibrate);
                    [[UIApplication sharedApplication] endIgnoringInteractionEvents];
                });
            }];
        }
        else {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:[NSString stringWithFormat:@"Video can not be saved\nPlease free some storage space"] delegate:self cancelButtonTitle:nil otherButtonTitles:nil, nil];
            [alert show];
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                [alert dismissWithClickedButtonIndex:0 animated:YES];
            });
        }

    }
}

但这就是问题所在。
录制的视频与预览中显示的不完全一样。请参阅这 2 个屏幕截图。

视频录制预览

视频播放视图

Answer 1

原因是因为你的iPad屏幕纵横比和相机纵横比不一样。

您可以通过设置 videoGravity 属性 of AVCaptureVideoPreviewLayer 来修改相机预览大小，这会影响内容相对于图层边界的查看方式：

layer.videoGravity = AVLayerVideoGravityResizeAspect;

但在那种情况下预览不会全屏。

如果您希望视频的宽高比与全屏预览时的宽高比相同，则必须对其进行裁剪。此处解释裁剪过程：

Exporting AVCaptureSession video in a size that matches the preview layer

Video capture with 1:1 aspect ratio in iOS

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