AVFoundation – 反转AVAsset并输出video文件

我已经看过这个问题几次，但他们都没有任何工作的答案。

需要反转并输出一个video文件（不能只是反向播放），保持与源video相同的压缩，格式和帧速率。

理想情况下，解决scheme将能够在内存或缓冲区中执行此操作，并避免将帧生成为图像文件（例如：使用AVAssetImageGenerator ），然后重新编译（资源密集，不可靠的时序结果，帧/图像质量从原始等）。

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我的贡献：这仍然不起作用，但迄今为止我已经尝试过的最好的：

• 使用AVAssetReader将示例帧读入CMSampleBufferRef[]的数组中。
• 用AVAssetWriter以相反的顺序写回来。
• 问题：似乎每个帧的时间保存在CMSampleBufferRef所以即使将它们追加也不行。
• 接下来，我尝试用反向/镜像帧交换每个帧的定时信息。
• 问题：这会导致AVAssetWriter发生未知错误。

• 下一步：我要查看AVAssetWriterInputPixelBufferAdaptor

   - (AVAsset *)assetByReversingAsset:(AVAsset *)asset { NSURL *tmpFileURL = [NSURL URLWithString:@"/tmp/test.mp4"]; NSError *error; // initialize the AVAssetReader that will read the input asset track AVAssetReader *reader = [[AVAssetReader alloc] initWithAsset:asset error:&error]; AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] lastObject]; AVAssetReaderTrackOutput* readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:videoTrack outputSettings:nil]; [reader addOutput:readerOutput]; [reader startReading]; // Read in the samples into an array NSMutableArray *samples = [[NSMutableArray alloc] init]; while(1) { CMSampleBufferRef sample = [readerOutput copyNextSampleBuffer]; if (sample == NULL) { break; } [samples addObject:(__bridge id)sample]; CFRelease(sample); } // initialize the the writer that will save to our temporary file. CMFormatDescriptionRef formatDescription = CFBridgingRetain([videoTrack.formatDescriptions lastObject]); AVAssetWriterInput *writerInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:nil sourceFormatHint:formatDescription]; CFRelease(formatDescription); AVAssetWriter *writer = [[AVAssetWriter alloc] initWithURL:tmpFileURL fileType:AVFileTypeMPEG4 error:&error]; [writerInput setExpectsMediaDataInRealTime:NO]; [writer addInput:writerInput]; [writer startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStamp((__bridge CMSampleBufferRef)samples[0])]; [writer startWriting]; // Traverse the sample frames in reverse order for(NSInteger i = samples.count-1; i >= 0; i--) { CMSampleBufferRef sample = (__bridge CMSampleBufferRef)samples[i]; // Since the timing information is built into the CMSampleBufferRef // We will need to make a copy of it with new timing info. Will copy // the timing data from the mirror frame at samples[samples.count - i -1] CMItemCount numSampleTimingEntries; CMSampleBufferGetSampleTimingInfoArray((__bridge CMSampleBufferRef)samples[samples.count - i -1], 0, nil, &numSampleTimingEntries); CMSampleTimingInfo *timingInfo = malloc(sizeof(CMSampleTimingInfo) * numSampleTimingEntries); CMSampleBufferGetSampleTimingInfoArray((__bridge CMSampleBufferRef)sample, numSampleTimingEntries, timingInfo, &numSampleTimingEntries); CMSampleBufferRef sampleWithCorrectTiming; CMSampleBufferCreateCopyWithNewTiming( kCFAllocatorDefault, sample, numSampleTimingEntries, timingInfo, &sampleWithCorrectTiming); if (writerInput.readyForMoreMediaData) { [writerInput appendSampleBuffer:sampleWithCorrectTiming]; } CFRelease(sampleWithCorrectTiming); free(timingInfo); } [writer finishWriting]; return [AVAsset assetWithURL:tmpFileURL]; } 

Answer 1

在过去的几天工作，并能够得到它的工作。

源代码在这里： http : //www.andyhin.com/post/5/reverse-video-avfoundation

使用AVAssetReader读取样本/帧，提取图像/像素缓冲区，然后附加镜像帧的显示时间。