Cannot convert rs2::frame into rs2::depth_frame when using callback method

[MoBaT]

Required Info
Camera Model	{ D435i }
Firmware Version	(0.2.0.926)
Operating System & Version	{ Ubuntu 18.04
Kernel Version (Linux Only)	( 5.3.0-51-generic )
Platform	x86_64 Desktop
SDK Version	{ v2.34.0 }
Language	{ C++ }

Issue Description

When using rs2::pipe().start(cfg, [](const rs2::frame & frame){ }), I am unable to get a proper depth_frame pointer when converting a frame to depth_frame. When using the rs2::pipe().wait_for_frames(), it works properly.

#define CALLBACK_METHOD

int main(int argc, char * argv[]) try
{
    rs2::context ctx;
    rs2::pipeline pipe(ctx);
    rs2::config cfg;

#ifdef CALLBACK_METHOD
    pipe.start(cfg, [&](const rs2::frame & frame) {
        if(frame.get_profile().stream_type() == RS2_STREAM_DEPTH)
        {
            auto depth_frame = frame.as<rs2::depth_frame>();
            if(!depth_frame)
            {
                std::cout << "ERROR: BAD DEPTH FRAME." << std::endl;
            }
        }
    });

     while(true)
    {
        usleep(10000);
    }
#else
    pipe.start(cfg);

    while(true)
    {
        auto frames = pipe.wait_for_frames();
        for(auto && frame : frames)
        {
            if(frame.get_profile().stream_type() == RS2_STREAM_DEPTH)
            {
                auto depth_frame = frame.as<rs2::depth_frame>();
                if(!depth_frame)
                {
                    std::cout << "ERROR: BAD DEPTH FRAME." << std::endl;
                }
            }
        }
    }
#endif
}

[ev-mp]

@MoBaT hello, the pipeline callbacks generally provide rs2::frameset objects types.
Therefore to extract the depth data use the following pattern

pipe.start(cfg, [&](const rs2::frame & frame) {
        //if(frame.get_profile().stream_type() == RS2_STREAM_DEPTH)  - This is not needed
        {
            if (rs2::frameset fs = frame.as<rs2::frameset>())
            {
                  // With callbacks, all the synchronized streams arrive in a single frameset
                 for (rs2::frame& f : fs)
                      ....
                 // Alternatively:
                 if (auto depth_frame = fs.get_depth_frame())
                      .....
           }
          else // // In case the rs2::frame is not cast-able to rs2::frameset
           { 
               ...
            }
    }

See the rs-callback example for more details

[RealSenseSupport]

Hi,

Will you be needing further help with this? If we don’t hear from you in 7 days, this issue will be closed.

Thanks