如何检查在iOS中的分辨率，视频的比特率 [英] How to check Resolution, bitrate of video in iOS

问题描述

我正在开发一个功能上的视频压缩;我的想法如下：

1. 获取视频的分辨率和位元率。


2. 视频。如果它大640x480，我会把这个视频压缩一半，并在1/4调整比特率。例如，如果视频分辨率为1920x1080，则其将被压缩为960x540，并且以4mbps的1920x1080将以1mbps压缩为960x540。

我有几个问题：

1. 如何在iOS中获得解析度和视频比特率？


2. 如果压缩1920x1080在一半到960x540，比特率也将自适应调整，还是我还需要手动设置比特率？




我试过下面的代码压缩视频，但我不知道压缩到哪个分辨率：

   - （void）convertVideoToLowQuailtyWithInputURL：（NSURL *）inputURL 
 outputURL：（NSURL *）outputURL 
 handler :( void（^）（AVAssetExportSession *））handler 
 {
 [[NSFileManager defaultManager] removeItemAtURL：outputURL error：nil]; 
 AVURLAsset * urlAsset = [AVURLAsset URLAssetWithURL：inputURL options：nil]; 
 
 AVAssetExportSession * session = [[AVAssetExportSession alloc] initWithAsset：urlAsset presetName：AVAssetExportPresetLowQuality]; 
 session.outputURL = outputURL; 
 session.outputFileType = AVFileTypeQuickTimeMovie; 
 [session exportAsynchronouslyWithCompletionHandler：^（void）
 {
 handler（session）; 
 
}]; 
} 
  

请给我一些建议。提前感谢。

解决方案

要获取视频的分辨率，请使用： -

  AVAssetTrack * videoTrack = nil; 
 AVURLAsset * asset = [AVAsset assetWithURL：[NSURL fileURLWithPath：originalVideo]]; 
 NSArray * videoTracks = [asset tracksWithMediaType：AVMediaTypeVideo]; 
 
 CMFormatDescriptionRef formatDescription = NULL; 
 NSArray * formatDescriptions = [videoTrack formatDescriptions]; 
 if（[formatDescriptions count]> 0）
 formatDescription =（CMFormatDescriptionRef）[formatDescriptions objectAtIndex：0]; 
 
 if（[videoTracks count]> 0）
 videoTrack = [videoTracks objectAtIndex：0]; 
 
 CGSize trackDimensions = {
 .width = 0.0，
 .height = 0.0，
}; 
 trackDimensions = [videoTrack naturalSize]; 
 
 int width = trackDimensions.width; 
 int height = trackDimensions.height; 
 NSLog（@Resolution =％d X％d，width，height）; 
  

您可以得到frameRate和bitrate如下： -

  float frameRate = [videoTrack nominalFrameRate]; 
 float bps = [videoTrack estimatedDataRate]; 
 NSLog（@Frame rate ==％f，frameRate）; 
 NSLog（@bps rate ==％f，bps）; 
  




I'm developing a video compression functionally; my ideas are below:

1. Getting resolution and bit-rate of video.
2. Check resolution of video. If it larger 640x480, I will compress this video in half and adjust the bit rate in 1/4 . E.g., if resolution of video is 1920x1080, it will be compressed to 960x540 and 1920x1080 at 4mbps will be compressed to 960x540 at 1mbps.

I have a few questions:

1. How can get resolution and bit-rate of video in iOS?
2. If compress 1920x1080 in half to 960x540, the bit-rate will also adaptively adjust, or do I still need to set the bitrate manually? How can do that?

I tried below code to compress video but I don't know it compressed to which resolution:

- (void)convertVideoToLowQuailtyWithInputURL:(NSURL*)inputURL
                                   outputURL:(NSURL*)outputURL
                                     handler:(void (^)(AVAssetExportSession*))handler
{
    [[NSFileManager defaultManager] removeItemAtURL:outputURL error:nil];
    AVURLAsset *urlAsset = [AVURLAsset URLAssetWithURL:inputURL options:nil];

    AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset: urlAsset presetName:AVAssetExportPresetLowQuality];
    session.outputURL = outputURL;
    session.outputFileType = AVFileTypeQuickTimeMovie;
    [session exportAsynchronouslyWithCompletionHandler:^(void)
     {
         handler(session);

     }];
}

Please give me some advice. Thanks in advance.

解决方案

To get the resolution of the video use this :-

AVAssetTrack *videoTrack = nil;
AVURLAsset *asset = [AVAsset assetWithURL:[NSURL fileURLWithPath:originalVideo]];
NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo];

CMFormatDescriptionRef formatDescription = NULL;
NSArray *formatDescriptions = [videoTrack formatDescriptions];
if ([formatDescriptions count] > 0)
    formatDescription = (CMFormatDescriptionRef)[formatDescriptions objectAtIndex:0];

if ([videoTracks count] > 0)
    videoTrack = [videoTracks objectAtIndex:0];

CGSize trackDimensions = {
    .width = 0.0,
    .height = 0.0,
};
trackDimensions = [videoTrack naturalSize];

int width = trackDimensions.width;
int height = trackDimensions.height;
NSLog(@"Resolution = %d X %d",width ,height);

you can get the frameRate and bitrate as follows:-

float frameRate = [videoTrack nominalFrameRate];
float bps = [videoTrack estimatedDataRate];
NSLog(@"Frame rate == %f",frameRate);
NSLog(@"bps rate == %f",bps);

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