關於視頻壓縮處理

最近在做關於視頻壓縮剪切的模塊，開始時是完全沒有思路，太費勁了，沒辦法靜下心來繼續研究，終於有點小成果，在此做個記錄，爲了自己下次的使用方便，也爲了能幫助到別人吧！

說一下需求： 我的需求是將一段視頻壓縮成指定格式（比如320 X 480），基於AVFoundation框架

下面上代碼：

storyBoard上直接拉拽UIButton，並關聯事件

#import <AVFoundation/AVFoundation.h>
#import "ParseViewController.h"

@interface ParseViewController ()

@end

@implementation ParseViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#param mark - Actions
- (IBAction)parse:(UIButton *)sender {
    [self exportVideo];
}

#param mark - Methods
- (void)exportVideo {
    // 爲了方便測試，我將一段視頻直接放到了桌面，從桌面加載的視頻，也將壓縮完成視頻放在桌面
    NSString *path = @"/Users/vs/Desktop/BeforParse.m4v"; // 來源路徑
    NSString *outputFilePath = @"/Users/vs/Desktop/hehe.mp4"; // 輸出路徑
    [self parseVideoWithInputUrl:[NSURL fileURLWithPath:path] outputUrl:[NSURL fileURLWithPath:outputFilePath] blockHandle:^(AVAssetExportSession *avAssetExportSession) {
        switch (avAssetExportSession.status) {
            case AVAssetExportSessionStatusFailed: // 失敗
                NSLog(@"exportSessionError: %@",avAssetExportSession.error.description);
                break;
            case AVAssetExportSessionStatusExporting:
                NSLog(@"AVAssetExportSessionExporting");
                break;
            case AVAssetExportSessionStatusCompleted: // 成功
                NSLog(@"exportSessionCompleted");
                dispatch_async(dispatch_get_main_queue(), ^{
                    [self performSelector:@selector(doSomeThings) withObject:self];
                });
                break;
        }
    }];
}

- (void)parseVideoWithInputUrl:(NSURL *)inputUrl outputUrl:(NSURL *)outputUrl blockHandle:(void(^)(AVAssetExportSession *avAssetExportSession)) handle {
    AVAsset *avAsset = [AVAsset assetWithURL:inputUrl];
    CMTime assetTime = [avAsset duration];
    float duration = CMTimeGetSeconds(assetTime);
    NSLog(@"視頻時長是：%f",duration);

    CMTime totalDuration = kCMTimeZero;
    AVMutableComposition *avMutableComposition = [AVMutableComposition composition];
    AVMutableCompositionTrack *avMutableCompTrack = [avMutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    AVAssetTrack *avAssetTack = [avAsset tracksWithMediaType:AVMediaTypeVideo][0];

    NSError *error = nil;
    // [avMutableCompTrack insertTimeRange:CMTimeRangeMake(CMTimeMake(0,12), CMTimeMake(12, duration)) ofTrack:avAssetTack atTime:kCMTimeZero error:&error];
    [avMutableCompTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration) ofTrack:avAssetTack atTime:kCMTimeZero error:&error];
    if (error) {
        NSLog(@"error: %@",error.description);
        return;
    }

    AVMutableVideoCompositionLayerInstruction *avMutableVideoCompositionLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:avMutableCompTrack];
    [avMutableVideoCompositionLayerInstruction setTransform:avAssetTack.preferredTransform atTime:kCMTimeZero];
    totalDuration = CMTimeAdd(totalDuration, assetTime);

    CGSize renderSize = CGSizeMake(0, 0);
    renderSize.width = avAssetTack.naturalSize.width;
    renderSize.height = avAssetTack.naturalSize.height;
    CGFloat rateW = 320/renderSize.width; // 設置壓縮比例
    CGFloat rateH = 480/renderSize.height;
    // 使用矩陣修改視頻的壓縮比例
    CGAffineTransform layerTransform = CGAffineTransformMake(avAssetTack.preferredTransform.a, avAssetTack.preferredTransform.b, avAssetTack.preferredTransform.c, avAssetTack.preferredTransform.d, avAssetTack.preferredTransform.tx * rateW, avAssetTack.preferredTransform.ty * rateH);
    layerTransform = CGAffineTransformConcat(layerTransform, CGAffineTransformMake(1, 0, 0, 1, 0, 0));
    layerTransform = CGAffineTransformMakeScale(rateW,rateH);
    [avMutableVideoCompositionLayerInstruction setTransform:layerTransform atTime:kCMTimeZero];
    [avMutableVideoCompositionLayerInstruction setOpacity:0.0 atTime:totalDuration];


    AVMutableVideoCompositionInstruction *avMutableVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    //    [avMutableVideoCompositionInstruction setTimeRange:CMTimeRangeMake(kCMTimeZero, [avMutableComposition duration])];
    avMutableVideoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, totalDuration);
    avMutableVideoCompositionInstruction.layerInstructions = [NSArray arrayWithObject:avMutableVideoCompositionLayerInstruction];

    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.instructions = [NSArray arrayWithObject:avMutableVideoCompositionInstruction];
    videoComposition.renderSize = CGSizeMake(320.f, 480.f); // 視頻的格式
    videoComposition.frameDuration = CMTimeMake(1, 10);

    AVAssetExportSession *avAssetExportSession = [[AVAssetExportSession alloc] initWithAsset:avMutableComposition presetName:AVAssetExportPreset640x480];
    [avAssetExportSession setVideoComposition:videoComposition];
    [avAssetExportSession setOutputFileType:AVFileTypeMPEG4];
    [avAssetExportSession setOutputURL:outputUrl];
    [avAssetExportSession setShouldOptimizeForNetworkUse:YES];
    [avAssetExportSession exportAsynchronouslyWithCompletionHandler:^{
        handle(avAssetExportSession);
    }];
}

- (void)doSomeThings {
    // 截取成功需要做的事情
}
@end

這樣對比一下壓縮處理過後的視頻，尺寸、大小都變了。這是我暫時研究出的，如有大家有好的demo,可以向我提出，因爲視頻這塊比較陌生，大家一起學習！
可以參考一下這個博客：blog.csdn.net/lookyou111/article/details/25625609