Writing YUV to file results in duplicated frames

Question

I am writing YUV (YV12) frames to YUV file. I am saving exactly 101 frames.But when I am playing the output YUV file I have 2x more frames whereas each second frame is always empty.

Here is my code:

            size_t lenght=_viewWidth * _viewHeight * 3;
    BYTE *bytes=(BYTE*)malloc(lenght);
    ///////////////  read pixels from tex  /////////////////////
    glBindTexture(GL_TEXTURE_2D,tex);
    glGetTexImage(GL_TEXTURE_2D,0,GL_RGB,GL_UNSIGNED_BYTE,bytes);
    glBindTexture(GL_TEXTURE_2D,0);

        BYTE *uvOut= new uint8_t[_viewWidth * _viewHeight *3];

            if(cfg.seqStart <= cfg.seqEnd)
    {
    hOutFile = fopen( outFileName.c_str(), cfg.appendMode ? "ab" : "wb" );
    assert(hOutFile!=0);



       RGBtoYUV420PSameSize(bytes,uvOut,3,0,_viewWidth,_viewHeight);

     fwrite(uvOut,_viewWidth* 3, _viewHeight, hOutFile); // Write V line

    fclose(hOutFile);
        cfg.seqStart++;
    }else{

        printf("done");

    }

    delete uvOut;
    free(bytes);

I run this block 101 times.I double checked it.Where does another frame come from ?

Answer 1

Don't know anything about opengl but the size of a frame in YV12-format is

width * height * 1.5

i.e. the croma-part is sub-sampled by a factor 2 horizontally and vertically. Above I see 3 a lot, change that value to 1.5 instead.

If you're interested in a YUV-format conversion tool checkout this which I wrote in python. And a viewer based on SDL here. Lot's of inspiration there :-)