Question

我正在使用AVAssetWriterVideoInput将缓冲区附加到文件中。我有这段代码：

 if ( _assetWriter.status == AVAssetWriterStatusWriting ) {
    // If the asset writer status is writing, append sample buffer to its corresponding asset writer input
    if (mediaType == AVMediaTypeVideo) {
      if (_assetWriterVideoInput.readyForMoreMediaData) {
        if (![_assetWriterVideoInput appendSampleBuffer:sampleBuffer]) {
          NSLog(@"error: %@", [_assetWriter.error localizedFailureReason]);
          NSLog(@"error: %@", [_assetWriter.error localizedRecoveryOptions]);
          NSLog(@"error: %@", [_assetWriter.error localizedDescription]);
          NSLog(@"error: %@", [_assetWriter.error domain]);
          NSLog(@"error: %@", [_assetWriter.error userInfo]);
        } else
          NSLog(@"frame saved");
      }
    }

这一行

    if (![_assetWriterVideoInput appendSampleBuffer:sampleBuffer]) {

以unknown error和代码-12738失败，显然在任何documentation上找不到，正如所有Apple文档所预期的那样。

另外，我怀疑这是一个未知的错误，原因很简单，因为AVFoundation中存在大量未知错误的代码，如果系统选择代码-12738，它显然知道的不仅仅是说它是未知的。

查看正在保存的文件，它保持0兆字节，因为没有保存缓冲区/帧。

此AVAssetWriterVideoInput的创建方式如下：

  CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions(currentFormatDescription);
  NSUInteger numPixels = dimensions.width * dimensions.height;
  NSUInteger bitsPerSecond;

  // Assume that lower-than-SD resolutions are intended for streaming, and use a lower bitrate
    NSUInteger bitsPerPixel = 11.4; // This bitrate matches the quality produced by AVCaptureSessionPresetHigh.

  bitsPerSecond = numPixels * bitsPerPixel;

  NSDictionary *videoCompressionSettings = @{AVVideoCodecKey                  : AVVideoCodecH264,
                                             AVVideoWidthKey                  : @(dimensions.width),
                                             AVVideoHeightKey                 : @(dimensions.height),
                                             AVVideoCompressionPropertiesKey  : @{ AVVideoAverageBitRateKey      : @(bitsPerSecond),
                                                                                   AVVideoMaxKeyFrameIntervalKey : @(30)}  };

  if ([_assetWriter canApplyOutputSettings:videoCompressionSettings forMediaType:AVMediaTypeVideo])
  {
    // Intialize asset writer video input with the above created settings dictionary
    _assetWriterVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
    _assetWriterVideoInput.expectsMediaDataInRealTime = YES;

和附加缓冲区时具有以下特征：

CMSampleBuffer 0x1009e12a0 retainCount: 1 allocator: 0x1b762cbb8
    invalid = NO
    dataReady = YES
    makeDataReadyCallback = 0x0
    makeDataReadyRefcon = 0x0
    formatDescription = <CMVideoFormatDescription 0x170443210 [0x1b762cbb8]> {
    mediaType:'vide' 
    mediaSubType:'BGRA' 
    mediaSpecific: {
        codecType: 'BGRA'       dimensions: 1920 x 1080 
    } 
    extensions: {<CFBasicHash 0x17087c2c0 [0x1b762cbb8]>{type = immutable dict, count = 2,
entries =>
    0 : <CFString 0x1b1c6d460 [0x1b762cbb8]>{contents = "Version"} = <CFNumber 0xb000000000000022 [0x1b762cbb8]>{value = +2, type = kCFNumberSInt32Type}
    2 : <CFString 0x1b1c6d3e0 [0x1b762cbb8]>{contents = "CVBytesPerRow"} = <CFNumber 0xb00000000001e002 [0x1b762cbb8]>{value = +7680, type = kCFNumberSInt32Type}
}
}
}
    sbufToTrackReadiness = 0x0
    numSamples = 1
    sampleTimingArray[1] = {
        {PTS = {290309939228910/1000000000 = 290309.939}, DTS = {INVALID}, duration = {INVALID}},
    }
    imageBuffer = 0x170321180

I have a sample code here如果您想检查问题。该代码准备以4K拍摄视频。如果您的设备无法执行此操作，请将行AVCaptureSessionPreset3840x2160更改为AVCaptureSessionPresetHigh inside ProcessadorVideo.m`。示例代码从视频流中裁剪出一个矩形，并对其应用漫画效果。感谢

Answer 1

我试过你的样本但无法重现错误-12783。但是我得到了另一个错误-12780。我使用iPhone 6s所以不确定是否是由于那个原因。

无论如何，我可以修复错误-12780。由于旧时间戳，您将面临此问题。我在您的应用程序中添加了一些日志以进行调试。见下文

2017-01-26 15：00：35.809590 NotWriting [16829：3116125]首字母为401051199680537 2017-01-26 15：00：35.809986 NotWriting [16829：3116125]附加时间戳的视频缓冲区401051199680537 2017-01-26 15：00：35.810008 NotWriting [16829：3116125] presentationTimeStamp小于最后一帧时间戳，所以可能会失败 2017-01-26 15：00：35.815605 NotWriting [16829：3116125]错误：发生未知错误（-12780）

当您编写缓冲区时，您必须确保演示文稿时间戳大于您编写的最后一帧，否则写入将失败。您可以使用以下逻辑添加检查：

CMTime  presentationTimeStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
      if(CMTIME_COMPARE_INLINE(presentationTimeStamp, <=, lastpresentationTimeStamp))
      {
          NSLog(@"presentationTimeStamp is less than last frame timestamp, So rejecting frame");
          return;
      }
      lastpresentationTimeStamp = presentationTimeStamp;

无法使用AVAssetWriterVideoInput将帧附加到视频文件。最后失败，未记录错误-12738

1 个答案: