iOS视频压缩

项目中涉及视频上传需求的, 为了上传和拉取速度体验, 节省存储费用, 都会在上传前进行视频压缩. 下面提供两种视频压缩实现, 仅供参考

第一种, 是采用 AVAssetExportSession 导出的方式, 优点是压缩快, 能有效的减少视频的文件大小, 但是定制化不友好, 压缩之后的视频画质确实令人不太满意, 实现代码如下

    //设置压缩的格式
    AVAssetExportSession *session=[AVAssetExportSession exportSessionWithAsset:asset presetName:AVAssetExportPresetMediumQuality];//mediumquality:中等质量
    session.videoComposition = [self getVideoComposition:asset];
    //设置导出路径
    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, true) lastObject] stringByAppendingPathComponent:[NSString stringWithFormat:@"%ld_compressedVideo.mp4",time(NULL)]];
    //设置到处路径
    session.outputURL=[NSURL fileURLWithPath:path];
    //设置输出文件的类型
    session.outputFileType=AVFileTypeMPEG4;
    //开辟子线程处理耗时操作
    [session exportAsynchronouslyWithCompletionHandler:^{
        NSLog(@"导出完成! 路径:%@",path);
    }];

第二种, 是采用 AVAssetReader和AVAssetWriter 实现逐帧压缩的方式, 优点是压缩的定制化比较好, 可以设置导出视频的编码格式,比特率, 帧率, 尺寸及视频质量, 压缩之后的画质令人满意, 缺点是视频时长较长时, 压缩时间较长, 实现代码如下:

///视频解码
+ (NSDictionary *)configVideoOutput{
    NSDictionary *videoOutputSetting = @{
    (__bridge NSString *)kCVPixelBufferPixelFormatTypeKey:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_422YpCbCr8]
  };
  return videoOutputSetting;
}

///音频解码
+ (NSDictionary *)configAudioOutput{
  NSDictionary *audioOutputSetting = @{
      AVFormatIDKey: @(kAudioFormatLinearPCM)
  };
  return audioOutputSetting;
}

/// 编码视频
+ (NSDictionary *)videoCompressSettting:(CGSize)videoSize frameRate:(NSInteger)frameRate estimatedDataRate:(float)estimatedDataRate{
  //写入视频大小
  float numPixels = videoSize.width * videoSize.height;
  //每像素比特
  CGFloat bitsPerPixel = 0.0;
  if (estimatedDataRate / numPixels > 1) {
      bitsPerPixel = 1.0;
  }else{
      bitsPerPixel = estimatedDataRate / numPixels - 0.1;
  }
  NSInteger bitsPerSecond = numPixels * bitsPerPixel;
  NSDictionary *compressProperties = @{
      AVVideoAverageBitRateKey : @(bitsPerSecond),
      AVVideoExpectedSourceFrameRateKey : @(frameRate),
      AVVideoProfileLevelKey : AVVideoProfileLevelH264HighAutoLevel
  };
  if (@available(iOS 11.0, *)) {
      NSDictionary *compressSetting = @{
          AVVideoCodecKey : AVVideoCodecTypeH264,
          AVVideoWidthKey : @(videoSize.width),
          AVVideoHeightKey : @(videoSize.height),
          AVVideoCompressionPropertiesKey : compressProperties,
          AVVideoScalingModeKey : AVVideoScalingModeResizeAspectFill
    };
    return compressSetting;
  } else {
    NSDictionary *compressSetting = @{
        AVVideoCodecKey : AVVideoCodecH264,
        AVVideoWidthKey : @(videoSize.width),
        AVVideoHeightKey : @(videoSize.height),
        AVVideoCompressionPropertiesKey : compressProperties,
        AVVideoScalingModeKey : AVVideoScalingModeResizeAspectFill
      };
      return compressSetting;
  }
}


/// 编码音频
+ (NSDictionary *)audioCompressSetting{
  AudioChannelLayout layout = {
      .mChannelLayoutTag = kAudioChannelLayoutTag_Stereo,
      .mChannelBitmap = 0,
      .mNumberChannelDescriptions = 0
  };
  NSData *data = [NSData dataWithBytes:&layout   length:offsetof(AudioChannelLayout, mChannelDescriptions)];
  NSDictionary *compressSettings = @{
      AVFormatIDKey : @(kAudioFormatMPEG4AAC),
      AVEncoderBitRateKey : @96000,
      AVSampleRateKey : @44100,
      AVChannelLayoutKey : data,
      AVNumberOfChannelsKey : @2
  };
  return compressSettings;
}

///视频大小及方向修正
+ (AVMutableVideoComposition *)getVideoComposition:(AVAsset *)asset {
  AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
  AVMutableComposition *composition = [AVMutableComposition composition];
  AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
  CGSize videoSize = videoTrack.naturalSize;

  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) ||
       (t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0)){
          videoSize = CGSizeMake(videoSize.height, videoSize.width);
      }
  }
  composition.naturalSize    = videoSize;
  videoComposition.renderSize = videoSize;
  videoComposition.frameDuration = CMTimeMake(1, videoTrack.nominalFrameRate);

  AVMutableCompositionTrack *compositionVideoTrack;
  compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
  [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:videoTrack atTime:kCMTimeZero error:nil];
  AVMutableVideoCompositionLayerInstruction *layerInst;
  layerInst = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
  [layerInst setTransform:videoTrack.preferredTransform atTime:kCMTimeZero];
  AVMutableVideoCompositionInstruction *inst = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
  inst.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
  inst.layerInstructions = [NSArray arrayWithObject:layerInst];
  videoComposition.instructions = [NSArray arrayWithObject:inst];
  return videoComposition;
}

  ///压缩代码
  AVAssetReader *reader = [AVAssetReader assetReaderWithAsset:asset error:nil];
  NSString *outPath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, true) lastObject] stringByAppendingPathComponent:[NSString stringWithFormat:@"%ld_compressedVideo.mp4",time(NULL)]];
  AVAssetWriter *writer = [AVAssetWriter assetWriterWithURL:[NSURL fileURLWithPath:outPath] fileType:AVFileTypeMPEG4 error:nil];
  AVAssetTrack *track;
  NSArray *array = asset.tracks;
  //获取视频大小...不用之前的naturalSize 方法是因为被弃用了
  CGSize videoSize = CGSizeZero;
  for (AVAssetTrack *atrack in array) {
      if ([atrack.mediaType isEqualToString:AVMediaTypeVideo]) {
         CGSize realSize = CGSizeApplyAffineTransform(atrack.naturalSize, atrack.preferredTransform);
        videoSize = CGSizeMake(fabs(realSize.width), fabs(realSize.height));
        track = atrack;
        break;
      }
  }
  NSLog(@"width = %f,height = %f",videoSize.width, videoSize.height);
  ///比特率小于1不压缩
  if (track.estimatedDataRate / (videoSize.width * videoSize.height) < 1) {
    return;
}

  AVAssetReaderVideoCompositionOutput *output = [AVAssetReaderVideoCompositionOutput assetReaderVideoCompositionOutputWithVideoTracks:@[track] videoSettings:[self configVideoOutput]];
  output.videoComposition = composition;

  NSInteger frameRate = 20;
  if (track.nominalFrameRate > 30) {
      frameRate = 30;
  }else{
      frameRate = track.nominalFrameRate - 5;
  }
  AVAssetWriterInput *videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:[self videoCompressSettting:videoSize frameRate:frameRate estimatedDataRate:track.estimatedDataRate]];
  if ([reader canAddOutput:output]) {
      [reader addOutput:output];
  }
  if ([writer canAddInput:videoInput]) {
      [writer addInput:videoInput];
  }

  AVAssetTrack *audioTrack = [[asset tracksWithMediaType:AVMediaTypeAudio] firstObject];
  AVAssetReaderTrackOutput *audioOutPut = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:[self configAudioOutput]];
  AVAssetWriterInput *audioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:[self audioCompressSetting]];
  if ([reader canAddOutput:audioOutPut]) {
      [reader addOutput:audioOutPut];
  }
  if ([writer canAddInput:audioInput]) {
      [writer addInput:audioInput];
  }

  [reader startReading];
  [writer startWriting];
  [writer startSessionAtSourceTime:kCMTimeZero];

  dispatch_group_t group = dispatch_group_create();
  dispatch_group_enter(group);
  dispatch_queue_t videoCompressQueue =   dispatch_queue_create("videoCompressQueue", NULL);
  [videoInput requestMediaDataWhenReadyOnQueue:videoCompressQueue usingBlock:^{
      while ([videoInput isReadyForMoreMediaData]) {
          CMSampleBufferRef sampleBufferRef;
          if ([reader status] == AVAssetReaderStatusReading && (sampleBufferRef = [output copyNextSampleBuffer])) {
            BOOL result = [videoInput appendSampleBuffer:sampleBufferRef];
            CFRelease(sampleBufferRef);
            if (!result) {
                [reader cancelReading];
                break;
            }
        }else{
            [videoInput markAsFinished];
            dispatch_group_leave(group);
            break;
        }
    }
  }];
  dispatch_group_enter(group);
  dispatch_queue_t audioCompressQueue =   dispatch_queue_create("audioCompressQueue", NULL);
  [audioInput requestMediaDataWhenReadyOnQueue:audioCompressQueue usingBlock:^{
    while ([audioInput isReadyForMoreMediaData]) {
        CMSampleBufferRef sampleBufferRef;
        if ([reader status] == AVAssetReaderStatusReading && (sampleBufferRef = [audioOutPut copyNextSampleBuffer])) {
            BOOL result = [audioInput appendSampleBuffer:sampleBufferRef];
            CFRelease(sampleBufferRef);
            if (!result) {
                [reader cancelReading];
                break;
            }
        }else{
            [audioInput markAsFinished];
            dispatch_group_leave(group);
            break;
        }
    }
 }];
  dispatch_group_notify(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    if ([reader status] == AVAssetReaderStatusReading) {
        [reader cancelReading];
    }
    switch (writer.status) {
        case AVAssetWriterStatusWriting:
        {
            [writer finishWritingWithCompletionHandler:^{
                NSLog(@"压缩完成");
            }];
        }
            break;
        default:
            break;
    }
  });

另外在压缩时, 需要判断视频的质量, 有些是已经压缩过的视频, 再度上传时, 就没有必要再压缩.