Question

我的主要目标是从服务器流式传输视频，并在流式传输时逐帧剪切（以便OpenGL可以使用它）。为此，我使用了我在互联网上随处可见的代码（我记得它来自Apple的GLVideoFrame示例代码）：

NSArray * tracks = [asset tracks];
NSLog(@"%d", tracks.count);

for(AVAssetTrack* track in tracks) {

    NSLog(@"type: %@", [track mediaType]);

    initialFPS = track.nominalFrameRate;
    width = (GLuint)track.naturalSize.width;
    height = (GLuint)track.naturalSize.height;


    NSError * error = nil;

    // _movieReader is a member variable
    @try {
        self._movieReader = [[[AVAssetReader alloc] initWithAsset:asset error:&error] autorelease];
    }
    @catch (NSException *exception) {
        NSLog(@"%@ -- %@", [exception name], [exception reason]);
        NSLog(@"skipping track");

        continue;
    }


    if (error)
    {
        NSLog(@"CODE:%d\nDOMAIN:%@\nDESCRIPTION:%@\nFAILURE_REASON:%@", [error code], [error domain], error.localizedDescription, [error localizedFailureReason]);                                          
        continue;
    }

    NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey;
    NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA];
    NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key]; 
    [_movieReader addOutput:[AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:track
                                                                       outputSettings:videoSettings]];
    [_movieReader startReading];
    [self performSelectorOnMainThread:@selector(frameStarter) withObject:nil waitUntilDone:NO];
}

但我总是在[[AVAssetReader alloc] initWithAsset:error:]获得此例外。

NSInvalidArgumentException -- *** -[AVAssetReader initWithAsset:error:] Cannot initialize an instance of AVAssetReader with an asset at non-local URL 'http://devimages.apple.com/iphone/samples/bipbop/bipbopall.m3u8'

所以我的两个问题是：

异常是否真的告诉我AVAssetReader必须有本地网址？它可以用于流式传输（就像AVFoundation类的其余部分一样）吗？
如果AVFoundation方法不起作用，那么有什么其他建议可以流式传输视频并同时拆分其帧？

非常感谢你的帮助。

Answer 1

您可以在AVMutableCompositionTrack上获取远程文件

AVURLAsset* soundTrackAsset = [[AVURLAsset alloc]initWithURL:[NSURL URLWithString:@"http://www.yoururl.com/yourfile.mp3"] options:nil];

AVMutableCompositionTrack *compositionAudioSoundTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioSoundTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, audioAsset.duration) 
                               ofTrack:[[soundTrackAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0] 
                                atTime:kCMTimeZero error:nil];

但是，对于压缩率较高的文件（如MP4s

），此方法效果不佳

使用AVAssetReader从远程资产中读取（流）

2 个答案: