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I got a decoded AVFrame whose format shows 160/Videotoolbox_vld. After googled some articles(here) and viewed the FFmpeg source code(here, and here), the CVBuffer handle should be at AVFrame.data[3]. But the CVBuffer I got seems invalid, any CVPixelBufferGetXXX() function returns 0 or nil.

If I used the av_hwframe_transfer_data() like the ffmpeg's example/hw_decode.c did, the sample can be downloaded from HW to SW buffer. Its AVFrame.format will be nv12. After converted via sws_scale to bgra, the sample can be showed on view with correct content.

I think the VideoToolbox decoded frame is OK. The way I convert AVFrame.data[3] to CVBuffer may be wrong. Just learned accessing c pointer in swift but I am not sure how to read a resource handle(CVBuffer) in a pointer correctly.

The following is how I try to extract CVBuffer from AVFrame

var pFrameOpt: UnsafeMutablePointer<AVFrame>? = av_frame_alloc()
avcodec_receive_frame(..., pFrameOpt)

let data3: UnsafeMutablePointer<UInt8>? = pFrameOpt?.pointee.data.3
data3?.withMemoryRebound(to: CVBuffer.self, capacity: 1) { pCvBuf in
    let fW = pFrameOpt!.pointee.width // print 3840
    let fH = pFrameOpt!.pointee.height // print 2160
    let fFmt = pFrameOpt!.pointee.format // print 160

    let cvBuf: CVBuffer = pCvBuf.pointee

    let a1 = CVPixelBufferGetDataSize(cvBuf)               // print 0
    let a2 = CVPixelBufferGetPixelFormatType(cvBuf)        // print 0
    let a3 = CVPixelBufferGetWidth(cvBuf)                  // print 0
    let a4 = CVPixelBufferGetHeight(cvBuf)                 // print 0
    let a5 = CVPixelBufferGetBytesPerRow(cvBuf)            // print 0
    let a6 = CVPixelBufferGetBytesPerRowOfPlane(cvBuf, 0)  // print 0
    let a7 = CVPixelBufferGetWidthOfPlane(cvBuf, 0)        // print 0
    let a8 = CVPixelBufferGetHeightOfPlane(cvBuf, 0)       // print 0
    let a9 = CVPixelBufferGetPlaneCount(cvBuf)             // print 0
    let a10 = CVPixelBufferIsPlanar(cvBuf)                 // print false
    let a11 = CVPixelBufferGetIOSurface(cvBuf)             // print nil
    let a12 = CVPixelBufferGetBaseAddress(cvBuf)           // print nil
    let a13 = CVPixelBufferGetBaseAddressOfPlane(cvBuf, 0) // print nil

    let b1 = CVImageBufferGetCleanRect(cvBuf)   // print 0, 0, 0, 0
    let b2 = CVImageBufferGetColorSpace(cvBuf)  // print nil 
    let b3 = CVImageBufferGetDisplaySize(cvBuf) // print 0, 0, 0, 0
    let b4 = CVImageBufferGetEncodedSize(cvBuf) // print 0, 0, 0, 0
    let b5 = CVImageBufferIsFlipped(cvBuf)      // print false

    // bad exec
    var cvTextureOut: CVMetalTexture?
    CVMetalTextureCacheCreateTextureFromImage(kCFAllocatorDefault, ..., cvBuf, nil, .bgra8Unorm, 3840, 2160, 0, ...) 


}
Chen OT
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4 Answers4

1

CVBuffer is not a fixed size, so rebinding the memory won't work in this way. You need to do this:

Unmanaged<CVBuffer>.fromOpaque(data!).takeRetainedValue()

However, the bottom line is FFmpeg's VideoToolbox backend is not creating a CVPixelBuffer with kCVPixelBufferMetalCompatibilityKey set to true. You won't be able to call CVMetalTextureCacheCreateTextureFromImage(...) successfully in any case.

You could consider using a CVPixelBufferPool with appropriate settings (including kCVPixelBufferMetalCompatibilityKey set to true) and then using VTPixelTransferSession to quickly copy FFmpeg's pixel buffer to your own.

Greg Cotten
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0

It seems like I wrongly cast void* to CVPixelBuffer* instead of casting void* directly to CVPixelBuffer. I cannot find a swift way to do such c style casting from pointer to numeric value. (Using as! CVPixelBuffer causes crash).

So I create a function for void* to CVPixelBufferRef in C code to do such casting job.

// util.h
#include <CoreVideo/CVPixelBuffer.h>
CVPixelBufferRef CastToCVPixelBuffer(void* p);

// util.c
CVPixelBufferRef CastToCVPixelBuffer(void* p)
{
    return (CVPixelBufferRef)p;
}

// BridgeHeader.h
#include "util.h"

Then pass the UnsafeMutablePointer<UInt8> in, get CVPixelBuffer handle out.

let pFrameOpt: UnsafeMutablePointer<AVFrame>? = ...
let data3: UnsafeMutablePointer<UInt8>? = pFrameOpt?.pointee.data.3

let cvBuf: CVBuffer = CastToCVPixelBuffer(data3).takeUnretainedValue()

let width = CVPixelBufferGetWidth(cvBuf)   // print 3840
let height = CVPixelBufferGetHeight(cvBuf) // print 2160
Chen OT
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    Just checked. My one-liner answer is correct and the most straightforward way to do this without needing to bring obj-c into the mix. – Greg Cotten Apr 01 '20 at 22:09
0

Try this

let cvBuf: CVBuffer = Array(UnsafeMutableBufferPointer(start: data3, count: 3))
.withUnsafeBufferPointer {
   $0.baseAddress!.withMemoryRebound(to: CVBuffer.self, capacity: 1) { $0 }
}.pointee

or maybe even

let cvBuf: CVBuffer = unsafeBitcast(UnsafeMutableBufferPointer(start: data3, count: 3), to: CVBuffer.self)
Kamil.S
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  • I had tried this and failed. All the CVPixelXX Getter function returns invalid data. I think it just converted to CVPixelBuffer* instead of CVPixelBuffer directly. – Chen OT Aug 24 '19 at 03:34
0
/**
    @function   CVPixelBufferGetBaseAddressOfPlane
    @abstract   Returns the base address of the plane at planeIndex in the PixelBuffer.
    @discussion Retrieving the base address for a PixelBuffer requires that the buffer base address be locked
                via a successful call to CVPixelBufferLockBaseAddress. On OSX 10.10 and earlier, or iOS 8 and
                earlier, calling this function with a non-planar buffer will have undefined behavior.
    @param      pixelBuffer Target PixelBuffer.
    @param      planeIndex  Identifying the plane.
    @result     Base address of the plane, or NULL for non-planar CVPixelBufferRefs.
*/
@available(iOS 4.0, *)
public func CVPixelBufferGetBaseAddressOfPlane(_ pixelBuffer: CVPixelBuffer, _ planeIndex: Int) -> UnsafeMutableRawPointer?

maybe you can try use CVPixelBufferLockBaseAddress before use CVPixelBufferGetBaseAddressOfPlane

cl zhu
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