最近做视频压缩上传功能 刚开始用的苹果已经简单封装好的 AVAssetExportSession 框架 视频压缩上传后 发现有些视频压缩后 反而变大了
后来参考了近期视频优化做的比较不错的douyin 发现不论上传多大的视频 被douyin压缩以后比特率（视频每秒传输的大小 单位：比特率（bps） / 千比特率（kbps））基本都维持在1500 kbps左右 经测试 这是对视频压缩后 文件大小 影响最大的一个参数
另外 还有比如帧率 视频宽高 等参数 也对视频压缩有一定的影响
用此方法 在项目中实测 基本可以满足绝大多数需求
如果你仅仅是想完成需求 不想研究代码的话
到这里可以结束阅读了
直接翻到最下面下载Demo 复制我封装好的方法 调用 就行了
继续往下看的话：
代码用到了访问相机 访问相册 访问麦克风 添加视频到相册四个权限
使用前 先把info中相机相册对应权限打开
info.plist 用Source Code方式打开的话 这样写：

    <key>NSCameraUsageDescription</key>
    <string>是否允许访问相机</string>
    <key>NSMicrophoneUsageDescription</key>
    <string>App需要您的同意才能访问麦克风</string>
    <key>NSPhotoLibraryUsageDescription</key>
    <string>是否允许访问相册</string>
    <key>NSPhotoLibraryAddUsageDescription</key>
    <string>是否允许添加视频或图片到相册</string>

info.plist 用Property List方式打开的话 这样配置：

info中相册相机权限

配置好了 开始写代码：
ViewController.m
使用系统的UIImagePickerController选择或者拍摄对应的视频
使用前 先遵守<UIImagePickerControllerDelegate, UINavigationControllerDelegate>这俩协议
然后写这个

@property (nonatomic, strong) UIImagePickerController *imagePicker;

从相册中选择视频 代码注释写的比较详细了

//从相册中选择视频
- (IBAction)chooseVideoBtnClick:(id)sender {
    if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeSavedPhotosAlbum])
    {
        self.imagePicker = [[UIImagePickerController alloc] init];
        self.imagePicker.delegate = self;
        /*
         * 设置资源文件来源 图库 相机 相册
         * UIImagePickerControllerSourceTypePhotoLibrary,
         * UIImagePickerControllerSourceTypeCamera,
         * UIImagePickerControllerSourceTypeSavedPhotosAlbum
         **/
        self.imagePicker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
        /*
         * 设置媒体类型
         * (NSString *)kUTTypeVideo 无声视频
         * (NSString *)kUTTypeMovie 有声视频
         * (NSString *)kUTTypeAudio 音频
         * 等...
         **/
        [self.imagePicker setMediaTypes:@[(NSString *)kUTTypeMovie]];
        self.imagePicker.videoQuality = UIImagePickerControllerQualityTypeHigh;
        [self presentViewController:self.imagePicker animated:YES completion:nil];
        
    }else{
        [self showAlertViewWithTitle:@"相机不可用" message:@"" withCancelButtonTitle:@"知道了"];
    }
}

相机拍摄视频

//拍摄视频
- (IBAction)recordVideoBtnClick:(id)sender {
    if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])
    {
        self.imagePicker = [[UIImagePickerController alloc] init];
        self.imagePicker.delegate = self;
        /*
         * 设置资源文件来源 图库 相机 相册
         * UIImagePickerControllerSourceTypePhotoLibrary,
         * UIImagePickerControllerSourceTypeCamera,
         * UIImagePickerControllerSourceTypeSavedPhotosAlbum
         **/
        self.imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
        /*
         * 设置媒体类型
         * (NSString *)kUTTypeVideo 无声视频
         * (NSString *)kUTTypeMovie 有声视频
         * (NSString *)kUTTypeAudio 音频
         * 等...
         **/
        [self.imagePicker setMediaTypes:@[(NSString *)kUTTypeMovie]];
        self.imagePicker.videoQuality = UIImagePickerControllerQualityTypeHigh;
        [self presentViewController:self.imagePicker animated:YES completion:nil];
        
    }else{
        [self showAlertViewWithTitle:@"相机不可用" message:@"" withCancelButtonTitle:@"知道了"];
    }
}

取消选择或者拍摄时的回调
UIImagePickerControllerDelegate

-(void)imagePickerControllerDidCancel:(UIImagePickerController *)picker{
    [self.imagePicker dismissViewControllerAnimated:YES completion:nil];
    [self showAlertViewWithTitle:@"用户取消操作" message:@"" withCancelButtonTitle:@"好的"];

}

视频选择 或者拍摄好以后回调

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<UIImagePickerControllerInfoKey,id> *)info{
//获取媒体类型
    NSString *type = [info objectForKey:UIImagePickerControllerMediaType];
    //媒体类型是视频时
    if ([type isEqualToString:@"public.movie"])
    {
        NSLog(@"===video URL = %@===", [info objectForKey:UIImagePickerControllerMediaURL]);
        //视频路径URL
        NSURL *outputUrl = [info objectForKey:UIImagePickerControllerMediaURL];
        //关闭相册界面
        [picker dismissViewControllerAnimated:YES completion:^{
        //执行视频压缩功能            
        [self compressVideoWithVideoUrl:outputUrl];
        }];
    }
}

//压缩视频

/*
 * 自定义视频压缩
 * videoUrl 原视频url路径 必传
 * outputBiteRate 压缩视频至指定比特率(bps) 可传nil 默认1500kbps
 * outputFrameRate 压缩视频至指定帧率 可传nil 默认30fps
 * outputWidth 压缩视频至指定宽度 可传nil 默认960
 * outputWidth 压缩视频至指定高度 可传nil 默认540
 * compressComplete 压缩后的视频信息回调 (id responseObjc) 可自行打印查看
 **/
- (void)compressVideoWithVideoUrl:(NSURL *)outputUrl{
    [VideoCompress compressVideoWithVideoUrl:outputUrl withBiteRate:@(1500 * 1024) withFrameRate:@(30) withVideoWidth:@(960) withVideoHeight:@(540) compressComplete:^(id responseObjc) {
        NSString *filePathStr = [responseObjc objectForKey:@"urlStr"];
        AVURLAsset *asset = [AVURLAsset assetWithURL:[NSURL fileURLWithPath:filePathStr]];
        AVAssetTrack *videoTrack = [asset tracksWithMediaType:AVMediaTypeVideo].firstObject;
        //视频大小 MB
        unsigned long long fileSize = [[NSFileManager defaultManager] attributesOfItemAtPath:filePathStr error:nil].fileSize;
        float fileSizeMB = fileSize / (1024.0*1024.0);
        //视频宽高
        NSInteger videoWidth = videoTrack.naturalSize.width;
        NSInteger videoHeight = videoTrack.naturalSize.height;
        //比特率
        NSInteger kbps = videoTrack.estimatedDataRate / 1024;
        //帧率
        NSInteger frameRate = [videoTrack nominalFrameRate];
        NSLog(@"\nfileSize after compress = %.2f MB,\n videoWidth = %ld,\n videoHeight = %ld,\n video bitRate = %ld\n, video frameRate = %ld", fileSizeMB, videoWidth, videoHeight, kbps, frameRate);
//        NSData *videoData = [NSData dataWithContentsOfFile:filePathStr];
        //                    NSData *videoData = [NSData dataWithContentsOfURL:asset.URL];
        //在这里上传或者保存已经处理好的视频文件
        //保存视频至相册
        UISaveVideoAtPathToSavedPhotosAlbum(filePathStr, self, @selector(videoSavedToPhotosAlbum:didFinishSavingWithError:contextInfo:), nil);
    }];
}

取消事件的一些弹框

- (void)showAlertViewWithTitle:(NSString*)title message:(NSString*)msg withCancelButtonTitle:(NSString *)cancelButtonTitle{
    UIAlertController* alertController = [UIAlertController alertControllerWithTitle:title message:@"" preferredStyle:UIAlertControllerStyleAlert];
    [alertController addAction:[UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
    }]];
    [self presentViewController:alertController animated:YES completion:nil];
}

//视频保存成功提示框

#pragma mark 保存视频后的回调
- (void)videoSavedToPhotosAlbum:(NSString *)videoUrlStr didFinishSavingWithError:(NSError*)error contextInfo:(id)contextInfo{
    NSString*message =@"提示";
    if(!error) {
        message = @"视频成功保存到相册";
    }else{
        message = [error description];
    }
    [self showAlertViewWithTitle:@"提示" message:message withCancelButtonTitle:@"确定"];
}

VideoCompress.m

/*
 * 自定义视频压缩
 * videoUrl 原视频url路径 必传
 * outputBiteRate 压缩视频至指定比特率(bps) 可传nil 默认1500kbps
 * outputFrameRate 压缩视频至指定帧率 可传nil 默认30fps
 * outputWidth 压缩视频至指定宽度 可传nil 默认960
 * outputWidth 压缩视频至指定高度 可传nil 默认540
 * compressComplete 压缩后的视频信息回调 (id responseObjc) 可自行打印查看
 **/
+ (void)compressVideoWithVideoUrl:(NSURL *)videoUrl withBiteRate:(NSNumber * _Nullable)outputBiteRate withFrameRate:(NSNumber * _Nullable)outputFrameRate withVideoWidth:(NSNumber * _Nullable)outputWidth withVideoHeight:(NSNumber * _Nullable)outputHeight compressComplete:(void(^)(id responseObjc))compressComplete{
    if (!videoUrl) {
        [SVProgressHUD showErrorWithStatus:@"视频路径不能为空"];
        return;
    }
    NSLog(@"===videoUrl.abs = %@, videoUrl.path = %@", videoUrl.absoluteString, videoUrl.path);
    NSInteger compressBiteRate = outputBiteRate ? [outputBiteRate integerValue] : 1500 * 1024;
    NSInteger compressFrameRate = outputFrameRate ? [outputFrameRate integerValue] : 30;
    NSInteger compressWidth = outputWidth ? [outputWidth integerValue] : 960;
    NSInteger compressHeight = outputHeight ? [outputHeight integerValue] : 540;
    //取出原视频详细资料
    AVURLAsset *asset = [AVURLAsset assetWithURL:videoUrl];
    //视频时长 S
    CMTime time = [asset duration];
    NSInteger seconds = ceil(time.value/time.timescale);
    if (seconds < 3) {
        [SVProgressHUD showErrorWithStatus:@"请上传3秒以上的视频"];
        return;
    }
    //压缩前原视频大小MB
    unsigned long long fileSize = [[NSFileManager defaultManager] attributesOfItemAtPath:videoUrl.path error:nil].fileSize;
    float fileSizeMB = fileSize / (1024.0*1024.0);
    //取出asset中的视频文件
    AVAssetTrack *videoTrack = [asset tracksWithMediaType:AVMediaTypeVideo].firstObject;
    //压缩前原视频宽高
    NSInteger videoWidth = videoTrack.naturalSize.width;
    NSInteger videoHeight = videoTrack.naturalSize.height;
    //压缩前原视频比特率
    NSInteger kbps = videoTrack.estimatedDataRate / 1024;
    //压缩前原视频帧率
    NSInteger frameRate = [videoTrack nominalFrameRate];
    NSLog(@"\noriginalVideo\nfileSize = %.2f MB,\n videoWidth = %ld,\n videoHeight = %ld,\n video bitRate = %ld\n, video frameRate = %ld", fileSizeMB, videoWidth, videoHeight, kbps, frameRate);
    NSMutableDictionary *dic = [NSMutableDictionary dictionaryWithDictionary:@{@"urlStr" : videoUrl.path}];
    //原视频比特率小于指定比特率 不压缩 返回原视频
    if (kbps <= (compressBiteRate / 1024)) {
        compressComplete(dic);
        return;
    }
    //指定压缩视频沙盒根目录
    NSString *cachesDir = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject];
    //添加文件完整路径
    NSString *outputUrlStr = [[cachesDir stringByAppendingPathComponent:@"videoTest"] stringByAppendingPathExtension:@"mp4"];
    NSLog(@"===压缩视频存放的指定路径%@===", outputUrlStr);
    //如果指定路径下已存在其他文件 先移除指定文件
    if ([[NSFileManager defaultManager] fileExistsAtPath:outputUrlStr]) {
        BOOL removeSuccess =  [[NSFileManager defaultManager] removeItemAtPath:outputUrlStr error:nil];
        if (!removeSuccess) {
            [SVProgressHUD showErrorWithStatus:@"旧文件移除失败"];
            return;
        }
    }
    //创建视频文件读取者
    AVAssetReader *reader = [AVAssetReader assetReaderWithAsset:asset error:nil];
    //从指定文件读取视频
    AVAssetReaderTrackOutput *videoOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:videoTrack outputSettings:[VideoCompress configVideoOutput]];
    //取出原视频中音频详细资料
    AVAssetTrack *audioTrack = [asset tracksWithMediaType:AVMediaTypeAudio].firstObject;
    //从音频资料中读取音频
    AVAssetReaderTrackOutput *audioOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:[VideoCompress configAudioOutput]];
    //将读取到的视频信息添加到读者队列中
    if ([reader canAddOutput:videoOutput]) {
        [reader addOutput:videoOutput];
    }
    //将读取到的音频信息添加到读者队列中
    if ([reader canAddOutput:audioOutput]) {
        [reader addOutput:audioOutput];
    }
    //视频文件写入者
    AVAssetWriter *writer = [AVAssetWriter assetWriterWithURL:[NSURL fileURLWithPath:outputUrlStr] fileType:AVFileTypeMPEG4 error:nil];
    //根据指定配置创建写入的视频文件
    AVAssetWriterInput *videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:[VideoCompress videoCompressSettingsWithBitRate:compressBiteRate withFrameRate:compressFrameRate withWidth:compressWidth WithHeight:compressHeight withOriginalWidth:videoWidth withOriginalHeight:videoHeight]];
    //根据指定配置创建写入的音频文件
    AVAssetWriterInput *audioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:[VideoCompress audioCompressSettings]];
    if ([writer canAddInput:videoInput]) {
        [writer addInput:videoInput];
        NSLog(@"videoInput==========videoInput");
    }
    if ([writer canAddInput:audioInput]) {
        [writer addInput:audioInput];
        NSLog(@"audioInput==========audioInput");
    }
    [SVProgressHUD showWithStatus:@"视频压缩中..."];
    [reader startReading];
    [writer startWriting];
    [writer startSessionAtSourceTime:kCMTimeZero];
    //创建视频写入队列
    dispatch_queue_t videoQueue = dispatch_queue_create("Video Queue", DISPATCH_QUEUE_SERIAL);
    //创建音频写入队列
    dispatch_queue_t audioQueue = dispatch_queue_create("Audio Queue", DISPATCH_QUEUE_SERIAL);
    //创建一个线程组
    dispatch_group_t group = dispatch_group_create();
    //进入线程组
    dispatch_group_enter(group);
    //队列准备好后 usingBlock
    [videoInput requestMediaDataWhenReadyOnQueue:videoQueue usingBlock:^{
        BOOL completedOrFailed = NO;
        while ([videoInput isReadyForMoreMediaData] && !completedOrFailed) {
            CMSampleBufferRef sampleBuffer = [videoOutput copyNextSampleBuffer];
            if (sampleBuffer != NULL) {
                [videoInput appendSampleBuffer:sampleBuffer];
                NSLog(@"===%@===", sampleBuffer);
                CFRelease(sampleBuffer);
            } else {
                completedOrFailed = YES;
                [videoInput markAsFinished];
                dispatch_group_leave(group);
            }
        }
    }];
    dispatch_group_enter(group);
    //队列准备好后 usingBlock
    [audioInput requestMediaDataWhenReadyOnQueue:audioQueue usingBlock:^{
        BOOL completedOrFailed = NO;
        while ([audioInput isReadyForMoreMediaData] && !completedOrFailed) {
            CMSampleBufferRef sampleBuffer = [audioOutput copyNextSampleBuffer];
            if (sampleBuffer != NULL) {
                BOOL success = [audioInput appendSampleBuffer:sampleBuffer];
                NSLog(@"===%@===", sampleBuffer);
                CFRelease(sampleBuffer);
                completedOrFailed = !success;
            } else {
                completedOrFailed = YES;
            }
        }
        if (completedOrFailed) {
            [audioInput markAsFinished];
            dispatch_group_leave(group);
        }
    }];
    //完成压缩
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        if ([reader status] == AVAssetReaderStatusReading) {
            [reader cancelReading];
        }
        switch (writer.status) {
            case AVAssetWriterStatusWriting:
            {
                [SVProgressHUD showSuccessWithStatus:@"视频压缩完成"];
                [writer finishWritingWithCompletionHandler:^{
                    [dic setObject:outputUrlStr forKey:@"urlStr"];
                    compressComplete(dic);
                }];
            }
                break;
            case AVAssetWriterStatusCancelled:
                [SVProgressHUD showInfoWithStatus:@"取消压缩"];
                break;
            case AVAssetWriterStatusFailed:
                NSLog(@"===error：%@===", writer.error);
                [SVProgressHUD showErrorWithStatus:[NSString stringWithFormat:@"%@",writer.error]];
                break;
            case AVAssetWriterStatusCompleted:
            {
                [SVProgressHUD showSuccessWithStatus:@"视频压缩完成"];
                [writer finishWritingWithCompletionHandler:^{
                    [dic setObject:outputUrlStr forKey:@"urlStr"];
                    compressComplete(dic);
                }];
            }
                break;
            default:
                break;
        }
    });
}

视频压缩的参数配置

+ (NSDictionary *)videoCompressSettingsWithBitRate:(NSInteger)biteRate withFrameRate:(NSInteger)frameRate withWidth:(NSInteger)width WithHeight:(NSInteger)height withOriginalWidth:(NSInteger)originalWidth withOriginalHeight:(NSInteger)originalHeight{
    /*
     * AVVideoAverageBitRateKey： 比特率（码率）每秒传输的文件大小 kbps
     * AVVideoExpectedSourceFrameRateKey：帧率 每秒播放的帧数
     * AVVideoProfileLevelKey：画质水平
     BP-Baseline Profile：基本画质。支持I/P 帧，只支持无交错（Progressive）和CAVLC；
     EP-Extended profile：进阶画质。支持I/P/B/SP/SI 帧，只支持无交错（Progressive）和CAVLC；
     MP-Main profile：主流画质。提供I/P/B 帧，支持无交错（Progressive）和交错（Interlaced），也支持CAVLC 和CABAC 的支持；
     HP-High profile：高级画质。在main Profile 的基础上增加了8×8内部预测、自定义量化、 无损视频编码和更多的YUV 格式；
     **/
    NSInteger returnWidth = originalWidth > originalHeight ? width : height;
    NSInteger returnHeight = originalWidth > originalHeight ? height : width;
    
    NSDictionary *compressProperties = @{
                                         AVVideoAverageBitRateKey : @(biteRate),
                                         AVVideoExpectedSourceFrameRateKey : @(frameRate),
                                         AVVideoProfileLevelKey : AVVideoProfileLevelH264HighAutoLevel
                                         };
    if (@available(iOS 11.0, *)) {
        NSDictionary *compressSetting = @{
                                          AVVideoCodecKey : AVVideoCodecTypeH264,
                                          AVVideoWidthKey : @(returnWidth),
                                          AVVideoHeightKey : @(returnHeight),
                                          AVVideoCompressionPropertiesKey : compressProperties,
                                          AVVideoScalingModeKey : AVVideoScalingModeResizeAspectFill
                                          };
        return compressSetting;
    }else {
        NSDictionary *compressSetting = @{
                                          AVVideoCodecKey : AVVideoCodecTypeH264,
                                          AVVideoWidthKey : @(returnWidth),
                                          AVVideoHeightKey : @(returnHeight),
                                          AVVideoCompressionPropertiesKey : compressProperties,
                                          AVVideoScalingModeKey : AVVideoScalingModeResizeAspectFill
                                          };
        return compressSetting;
    }
}

音频压缩的参数配置

//音频设置
+ (NSDictionary *)audioCompressSettings{
    AudioChannelLayout stereoChannelLayout = {
        .mChannelLayoutTag = kAudioChannelLayoutTag_Stereo,
        .mChannelBitmap = kAudioChannelBit_Left,
        .mNumberChannelDescriptions = 0,
    };
    NSData *channelLayoutAsData = [NSData dataWithBytes:&stereoChannelLayout length:offsetof(AudioChannelLayout, mChannelDescriptions)];
    NSDictionary *audioCompressSettings = @{
                                            AVFormatIDKey : @(kAudioFormatMPEG4AAC),
                                            AVEncoderBitRateKey : @(128000),
                                            AVSampleRateKey : @(44100),
                                            AVNumberOfChannelsKey : @(2),
                                            AVChannelLayoutKey : channelLayoutAsData
                                            };
    return audioCompressSettings;
}

读取音频参数配置

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

读取视频参数配置

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

githubDemo链接