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一、MOV/MP4视频文件中的Rotation元数据

注：

实际上视频文件的Rotation元数据并不是保存的角度值，不过如果只关心角度问题而不是图像拉伸之类的，可以这样简单理解。关于如何获取Rotation元数据角度值，有兴趣的可以参看 vlc的源码。

 

二、常见视频播放器对方向的识别

三、MPMoviePlayerViewController控制视频方向

//…...
    NSString * url = @"http://www.yourdomain.com/Videos/1.m3u8";
    MPMoviePlayerViewController * vc = [[MPMoviePlayerViewController alloc] init];
    vc.moviePlayer.contentURL = [NSURL URLWithString:url];
    // 这里播放一个Rotation为90的视频，即Home键在下录制的视频
    [self rotateVideoView:vc degrees:90];
    [self presentMoviePlayerViewControllerAnimated:vc];
    [vc.moviePlayer play];
 
//…...
- (void)rotateVideoView:(MPMoviePlayerViewController *)movePlayerViewController degrees:(NSInteger)degrees
{
    if(degrees==0||degrees==360) return;
    if(degrees<0) degrees = (degrees % 360) + 360;
    if(degrees>360) degrees = degrees % 360;
    // MPVideoView在iOS8中Tag为1002，不排除苹果以后更改的可能性。参考递归查看View层次结构的lldb命令： (lldb) po [movePlayerViewController.view recursiveDescription]
    UIView *videoView = [movePlayerViewController.view viewWithTag:1002];
    if ([videoView isKindOfClass:NSClassFromString(@"MPVideoView")]) {
        videoView.transform = CGAffineTransformMakeRotation(M_PI * degrees / 180.0);
        videoView.frame = movePlayerViewController.view.bounds;
    }
}

#import "MPMoviePlayerViewController+Rotation.h"

@implementation MPMoviePlayerViewController (Rotation)

- (void)rotateVideoViewWithDegrees:(NSInteger)degrees
{
    if(degrees==0||degrees==360) return;
    if(degrees<0) degrees = (degrees % 360) + 360;
    if(degrees>360) degrees = degrees % 360;
   
    // MPVideoView在iOS8中Tag为1002，不排除苹果以后更改的可能性。参考递归查看View层次结构的lldb命令： (lldb) po [movePlayerViewController.view recursiveDescription]
    UIView *videoView = [self.view viewWithTag:1002];
    if ([videoView isKindOfClass:NSClassFromString(@"MPVideoView")]) {
        videoView.transform = CGAffineTransformMakeRotation(M_PI * degrees / 180.0);
        videoView.frame = self.view.bounds;
    }
}

@end

五、使用ffmpeg写入Rotation元数据 

注：

如果愿意，写入非0、90、180或270的值，比如45之类的也是可以的。  

六、获取视频方向(角度) 

+ (NSUInteger)degressFromVideoFileWithURL:(NSURL *)url
{
    NSUInteger degress = 0;
   
    AVAsset *asset = [AVAsset assetWithURL:url];
    NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
    if([tracks count] > 0) {
        AVAssetTrack *videoTrack = [tracks objectAtIndex:0];
        CGAffineTransform t = videoTrack.preferredTransform;
       
        if(t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0){
            // Portrait
            degress = 90;
        }else if(t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0){
            // PortraitUpsideDown
            degress = 270;
        }else if(t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0){
            // LandscapeRight
            degress = 0;
        }else if(t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0){
            // LandscapeLeft
            degress = 180;
        }
    }
   
    return degress;
}

七、按正确方向对视频进行截图

+ (UIImage *)extractImageFromVideoFileWithUrl:(NSURL *)url
{
    NSDictionary *opts = @{AVURLAssetPreferPreciseDurationAndTimingKey:@(NO)};
    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:url options:opts];
    AVAssetImageGenerator *gen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    // 应用方向
    gen.appliesPreferredTrackTransform = YES;
    CMTime time = CMTimeMakeWithSeconds(1, 60);
    NSError *error = nil;
    CMTime actualTime;
    CGImageRef image = [gen copyCGImageAtTime:time actualTime:&actualTime error:&error];
    if(error)
    {
        DLog(@"%@ %@",__FUNCTION_FILE_LINE__,error);
        return nil;
    }
    UIImage *thumb = [[UIImage alloc] initWithCGImage:image];
    CGImageRelease(image);
   
    return thumb;
}

八、实时视频的方向处理

注：

这种涉及大量内存拷贝的操作，实际应用中要权衡其利弊。以下代码未经过测试。

1、RGB24旋转90度  

// RGB24旋转90度
void RGB24Rotate90(int8_t *des, const int8_t *src, int width, int height)
{
    if(!des || !src) return;
   
    int n = 0;
    int linesize = width * 3;
    int i, j;
    // 逆时针旋转
    for (j = width; j > 0; j--) {
        for (i = 0; i < height; i++) {
            memccpy(&des[n], &src[linesize * i + j * 3 - 3], 0, 3);
            n += 3;
        }
    }
    /*
    // 顺时针旋转
    for (j = 0 ; j < width; j++) {
        for (i = height; i > 0; i--) {
            memccpy(&des[n], &src[linesize * (i - 1) + j * 3 - 3], 0, 3);
            n += 3;
        }
    }
    */
} 

2、RGB24旋转90度  

// YUV420旋转90度
void YUV420Rotate90(int8_t *des, const int8_t *src, int width, int height)
{
    int i = 0, j = 0, n = 0;
    int hw = width / 2, hh = height / 2;
   
    const int8_t *ptmp = src;
    for (j = width; j > 0; j--) {
        for (i = 0; i < height; i++) {
            des[n++] = ptmp[width * i + j];
        }
    }
   
    ptmp = src + width * height;
    for (j = hw; j > 0; j--) {
        for (i = 0; i < hh; i++) {
            des[n++] = ptmp[hw * i + j];
        }
    }
   
    ptmp = src + width * height * 5 / 4;
    for (j = hw; j > 0; j--) {
        for (i = 0; i < hh; i++) {
            des[n++] = ptmp[hw * i + j];
        }
    }
}

或：

int8_t[] rotateYUV420Degree90(int8_t[] data, int imageWidth, int imageHeight)
{
    int8_t [] yuv = new int8_t[imageWidth*imageHeight*3/2];
    // Rotate the Y luma
    int i = 0;
    for(int x = 0;x < imageWidth;x++)
    {
        for(int y = imageHeight-1;y >= 0;y--)
        {
            yuv[i] = data[y*imageWidth+x];
            i++;
        }
    }
    // Rotate the U and V color components
    i = imageWidth*imageHeight*3/2-1;
    for(int x = imageWidth-1;x > 0;x=x-2)
    {
        for(int y = 0;y < imageHeight/2;y++)
        {
            yuv[i] = data[(imageWidth*imageHeight)+(y*imageWidth)+x];
            i--;
            yuv[i] = data[(imageWidth*imageHeight)+(y*imageWidth)+(x-1)];
            i--;
        }
    }
    return yuv;
}

九、参考资料： 

[iOS]关于视频方向的若干问题

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原文地址：http://my.oschina.net/are1OfBlog/blog/501228