屏幕录制的视频在iOS 8中崩溃

Question

Here are the description of my code

Mainly crash getting on these two line.

BOOL success = [_avAdaptor appendPixelBuffer:pixelBuffer withPresentationTime:time]; if (!success) { NSLog(@"Warning: Unable to write buffer to video"); }

if (dispatch_semaphore_wait(_frameRenderingSemaphore, DISPATCH_TIME_NOW) != 0) {
    return;
}
dispatch_async(_render_queue, ^{
    if (![_videoWriterInput isReadyForMoreMediaData]) return;

    if (!self.firstTimeStamp) {
        self.firstTimeStamp = _displayLink.timestamp;
    }
    CFTimeInterval elapsed = (_displayLink.timestamp - self.firstTimeStamp);
    CMTime time = CMTimeMakeWithSeconds(elapsed, 1000);

    CVPixelBufferRef pixelBuffer = NULL;
    CGContextRef bitmapContext = [self createPixelBufferAndBitmapContext:&pixelBuffer];

    if (self.delegate) {
        [self.delegate writeBackgroundFrameInContext:&bitmapContext];
    }
    // draw each window into the context (other windows include UIKeyboard, UIAlert)
    // FIX: UIKeyboard is currently only rendered correctly in portrait orientation
    dispatch_sync(dispatch_get_main_queue(), ^{
        UIGraphicsPushContext(bitmapContext); {
            for (UIWindow *window in [[UIApplication sharedApplication] windows]) {
                [window drawViewHierarchyInRect:CGRectMake(0, 0, _viewSize.width, _viewSize.height) afterScreenUpdates:NO];
            }
        } UIGraphicsPopContext();
    });

    // append pixelBuffer on a async dispatch_queue, the next frame is rendered whilst this one appends
    // must not overwhelm the queue with pixelBuffers, therefore:
    // check if _append_pixelBuffer_queue is ready
    // if it’s not ready, release pixelBuffer and bitmapContext
    if (dispatch_semaphore_wait(_pixelAppendSemaphore, DISPATCH_TIME_NOW) == 0) {
        dispatch_async(_append_pixelBuffer_queue, ^{
            **BOOL success = [_avAdaptor appendPixelBuffer:pixelBuffer withPresentationTime:time];
            if (!success) {
                NSLog(@"Warning: Unable to write buffer to video");
            }**
            CGContextRelease(bitmapContext);
            CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
            CVPixelBufferRelease(pixelBuffer);

            dispatch_semaphore_signal(_pixelAppendSemaphore);
        });
    } else {
        CGContextRelease(bitmapContext);
        CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
        CVPixelBufferRelease(pixelBuffer);
    }

    dispatch_semaphore_signal(_frameRenderingSemaphore);
});

Also error description is

thread #34: tid = 0x4aefc, 0x00000001958952bc libsystem_platform.dylib _platform_memmove + 108, queue = 'ASScreenRecorder.append_queue', stop reason = EXC_BAD_ACCESS (code=1, address=0x109c60000) frame #0: 0x00000001958952bc libsystem_platform.dylib _platform_memmove + 108 frame #1: 0x0000000183c32004 CoreMedia FigNEAtomWriterAppendData + 92. frame #2: 0x0000000183c31f8c CoreMedia sbufAtom_appendAtomWithMemoryBlock + 104 frame #3: 0x0000000183c2f78c CoreMedia sbufAtom_createSerializedDataForPixelBuffer + 588 frame #4: 0x0000000183c2f4b8 CoreMedia FigRemote_CreateSerializedAtomDataForPixelBuffer + 288 frame #5: 0x0000000185a6af3c MediaToolbox remoteWriter_AddPixelBuffer + 140 frame #6: 0x0000000181bcebd4 AVFoundation -[AVFigAssetWriterTrack addPixelBuffer:atPresentationTime:error:] + 176 frame #7: 0x0000000181bca848 AVFoundation -[AVAssetWriterInputWritingHelper appendPixelBuffer:withPresentationTime:] + 124 frame #8: 0x0000000181bc82fc AVFoundation -[AVAssetWriterInput _appendPixelBuff er:withPresentationTime:] + 88 frame #9: 0x0000000181bcdb40 AVFoundation -[AVAssetWriterInputPixelBufferAdaptor appendPixelBuffer:withPresentationTime:] + 104 frame #10: 0x00000001000f45e0 Island Guide Aruba __35-[ASScreenRecorder writeVideoFrame]_block_invoke192(.block_descriptor=) + 132 at ASScreenRecorder.m:301 frame #11: 0x00000001005b0fd4 libdispatch.dylib _dispatch_call_block_and_release + 24 frame #12: 0x00000001005b0f94 libdispatch.dylib _dispatch_client_callout + 16 frame #13: 0x00000001005bbdb8 libdispatch.dylib _dispatch_queue_drain + 780 frame #14: 0x00000001005b42c4 libdispatch.dylib _dispatch_queue_invoke + 132 frame #15: 0x00000001005be5d4 libdispatch.dylib _dispatch_root_queue_drain + 772 frame #16: 0x00000001005c0248 libdispatch.dylib _dispatch_worker_thread3 + 132 frame #17: 0x000000019589d21c libsystem_pthread.dylib`_pthread_wqthread + 816

========================================================================

Answer 1

I assume you're using ASScreenRecorder (as couple of lines are identical to that repo). So I spent on this crash couple of days and probably found the issue, there is problem with creating pixel buffer pool (in [self createPixelBufferAndBitmapContext:&pixelBuffer]; method). Code modified by me:

- (void)writeVideoFrame{
  dispatch_async(_render_queue, ^{
    if (![_videoWriterInput isReadyForMoreMediaData]){
      return;
    }

    CVPixelBufferRef pixelBuffer = NULL;
    CVPixelBufferCreate(kCFAllocatorDefault, _viewSize.width, _viewSize.height, kCVPixelFormatType_32BGRA, (__bridge CFDictionaryRef _Nullable)(_outputBufferPoolAuxAttributes), &pixelBuffer);
    CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

    //creating bitmap context
    CGContextRef bitmapContext = NULL;
    bitmapContext = CGBitmapContextCreate(CVPixelBufferGetBaseAddress(pixelBuffer),
                                          CVPixelBufferGetWidth(pixelBuffer),
                                          CVPixelBufferGetHeight(pixelBuffer),
                                          8, CVPixelBufferGetBytesPerRow(pixelBuffer), _rgbColorSpace,
                                          kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst
                                          );

    CGContextScaleCTM(bitmapContext, _scale, _scale);
    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, _viewSize.height);
    CGContextConcatCTM(bitmapContext, flipVertical);

    dispatch_sync(dispatch_get_main_queue(), ^{
      UIGraphicsPushContext(bitmapContext); {
        [[UIApplication sharedApplication].keyWindow drawViewHierarchyInRect:CGRectMake(0, 0, _viewSize.width, _viewSize.height) afterScreenUpdates:NO];
      } UIGraphicsPopContext();
    });

    CMTime time = CMTimeAdd(_firstAudioTimeStamp, CMTimeMakeWithSeconds([[NSDate date] timeIntervalSinceDate:_startedAt], _firstAudioTimeStamp.timescale));
    [_avAdaptor appendPixelBuffer:pixelBuffer withPresentationTime:time];

    CGContextRelease(bitmapContext);
    CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
    CVPixelBufferRelease(pixelBuffer);
  });
}

So as you see I don't use CVPixelBufferPoolRef and CVPixelBufferPoolCreatePixelBuffer , just create CVPixelBufferRef everytime with CVPixelBufferCreate method. It's probably slower, but I haven't got crash even once since modified this.

Answer 2

I have this issue too. My workaround was trying to retain the buffer:

    CVPixelBufferRef pixelBuffer = NULL;
    CVPixelBufferRetain(pixelBuffer); // hope to retain the buffer
    CGContextRef bitmapContext = [self createPixelBufferAndBitmapContext:&pixelBuffer];

It seems to work without crash.