ShengQiangLiu / MetalMergeStreams

Use Metal to merge front camera stream and video stream. Save into Photos or Live

Metal merge streams

Use Metal to merge CVPixelBuffers and resize CVPixelBuffer in hight performance.

Merge frames

• Time consuming 0.2 ~ 1.5 ms can make sure the living real-time.
• Inputs are tow CVPixelBuffers. CVPixelBuffer-A (from front camera) and CVPixelBuffer-B (from video 'rtpVideo.mp4'). Output is new CVPixelBuffers.
• Upload pixel buffer as MTLTexture and in-frame location to GPU
• MTLComputeCommandEncoder compute new texture

Resize frame

• Input is CVPixelBuffers. Output is new CVPixelBuffers.
• MPSImageBilinearScale to resize pixel buffer, support mode ScaleToFill,ScaleAspectFit,ScaleAspectFill

Tow method to create new pixel buufer.

With pixel buffer pool

• Time consuming 1 ~ 2 ms.
• Create output CVPixelBuffer from Pixel CVPixelBufferPool
• Create a new MTLTexture from output CVPixelBuffer
• Compute and wait for completion
• Return the result CVPixelBuffer which is IOSurface-backed

Without pixel buffer pool

• Time consuming 6 ~ 7 ms.
• Create a texture from MTLDevice
• Compute and wait for completion
• MTLBlitCommandEncoder copy computed texture from GPU to CPU as MTLBuffer
• Create output CVPixelBuffer from MTLBuffer, but the output CVPixelBuffer is not IOSurface-backed
• Deep copy output CVPixelBuffer and config the copied output is IOSurface-backed