iOS 13.1.3 VTDecompressionSessionDecodeFrame can't decode right

Question

CVPixelBufferRef outputPixelBuffer = NULL;

CMBlockBufferRef blockBuffer = NULL;
void* buffer = (void*)[videoUnit bufferWithH265LengthHeader];
OSStatus status  = CMBlockBufferCreateWithMemoryBlock(kCFAllocatorDefault,
                                                      buffer,
                                                      videoUnit.length,
                                                      kCFAllocatorNull,
                                                      NULL, 0, videoUnit.length,
                                                      0, &blockBuffer);
if(status == kCMBlockBufferNoErr) {
    CMSampleBufferRef sampleBuffer = NULL;
    const size_t sampleSizeArray[] = {videoUnit.length};
    status = CMSampleBufferCreateReady(kCFAllocatorDefault,
                                       blockBuffer,
                                       _decoderFormatDescription ,
                                       1, 0, NULL, 1, sampleSizeArray,
                                       &sampleBuffer);
    if (status == kCMBlockBufferNoErr && sampleBuffer && _deocderSession) {
        VTDecodeFrameFlags flags = 0;
        VTDecodeInfoFlags flagOut = 0;
        OSStatus decodeStatus = VTDecompressionSessionDecodeFrame(_deocderSession,
                                                                  sampleBuffer,
                                                                  flags,
                                                                  &outputPixelBuffer,
                                                                  &flagOut);

        if(decodeStatus == kVTInvalidSessionErr) {
            NSLog(@"IOS8VT: Invalid session, reset decoder session");
        } else if(decodeStatus == kVTVideoDecoderBadDataErr) {
            NSLog(@"IOS8VT: decode failed status=%d(Bad data)", decodeStatus);
        } else if(decodeStatus != noErr) {
            NSLog(@"IOS8VT: decode failed status=%d", decodeStatus);
        }

        CFRelease(sampleBuffer);
    }
    CFRelease(blockBuffer);
}

return outputPixelBuffer;

This is my code to decode the stream data.It was working good on iPhone 6s,but when the code running on iPhoneX or iphone11, the "outputPixelBuffer" return a nil. Can anyone help?

Answer 1

Without seeing the code for your decompressionSession creation, it is hard to say. It could be that your decompressionSession is providing the outputBuffer to the callback function provided at creation, so I highly recommend you add that part of your code too.

By providing &outputPixelBuffer in:

OSStatus decodeStatus = VTDecompressionSessionDecodeFrame(_deocderSession,
                                                                  sampleBuffer,
                                                                  flags,
                                                                  &outputPixelBuffer,
                                                                  &flagOut);

only means that you've provided the reference, it does not mean that it will be synchronously filled for certain.

I also recommend that you print out the OSStatus for:

CMBlockBufferCreateWithMemoryBlock

and

CMSampleBufferCreateReady

And if there's issues at those steps, there should be a way to know.