Data Convert Backend

BMF Data Convert Backend


An all-in-one solution is needed when multiple dimension factors are involved in video process pipeline such as CPU/GPU devices, YUV420/NV12 or RGB24/RGB48, and AVFrame or Torch structure. As a framework, each module just focuses on its own target and data requirement, but it becomes complex when multiple modules work together as below supper resolution pipeline:

We can see that different modules have their own data requirements. The decode module outputs FFmpeg AVFrame in YUV420 pixel format, which is located on the CPU memory. The Trt SR module requires that the input data is an RGB24 torch after hardware acceleration and is located on the GPU memory. For SR through the Trt module, the output data needs to be encoded by the GPU, so the HW encode module can get AVFrame with NV12 pixel format located on the GPU memory and encode it by the GPU.

It tends to include the capabilities of video data conversion below:

  • pixel format and color space
  • devices between CPU and GPU
  • different media types such as avframe, cvmat and torch

Currently, the backend interface is under testing and demo integration. The fully unified and easy to use interface and examples for both C++ and Python will be released soon.

C++ Interface

/** @addtogroup bmf_backend_convert
 * @{
 * @arg src_vf: src VideoFrame
 * @arg src_dp: src MediaDesc that describe src_vf's attributes
 * @arg dst_dp: The desired MediaDesc of the converted VideoFrame.
 * @} */
BMF_API VideoFrame bmf_convert(VideoFrame& src_vf, const MediaDesc &src_dp, const MediaDesc &dst_dp);

This interface allows the conversion of a source VideoFrame to a destination VideoFrame. If the media_type in the source MediaDesc is different from the media_type in the destination MediaDesc, it indicates that the conversion will involve the transformation between VideoFrame and a third-party data structure. Accessing the third-party data structure requires the use of the private_attach and private_get methods of the VideoFrame.

VideoFrame scale and colorspace conversion

use bmf_convert do scale and csc

    MediaDesc dp;
    auto rgbformat = hmp::PixelInfo(hmp::PF_RGB24);
    auto src_vf = VideoFrame::make(640, 320, rgbformat);
    auto dst_vf = bmf_convert(src_vf, MediaDesc{},  dp);
    EXPECT_EQ(dst_vf.width(), 1920);
    EXPECT_EQ(dst_vf.height(), 960);
    EXPECT_EQ(dst_vf.frame().format(), hmp::PF_YUV420P);

Device memory transfer

Samples show how to transfer the input video frame memory on GPU memory.

    MediaDesc dp;
    dp.device(hmp::Device("gpu")); // or hmp::Device("cpu")
    auto dst_vf = bmf_convert(src_vf, MediaDesc{},  dp);

Conversion between VideoFrame and third-party data structure

BMF support the following types of third-party structure conversion with VideoFrame

  1. FFmpeg AVFrame
  2. Opencv cv::Mat
  3. libtorch at::Tensor

Here, FFmpeg AVFrame is used as an example to illustrate the conversion. Other types of conversions can be referred to in the test_convert_backend.cpp.

VideoFrame to ffmpeg AVFrame
  1. include <bmf/sdk/av_convertor.h>, this will register AVConvertor for AVFrame
  2. dst_dp set media_type with value MediaType::kAVFrame
  3. do bmf_convert, check if the return VideoFrame is a valid VideoFrame
  4. use private_get<AVFrame> to get the AVFrame pointer from the return VideoFrame.

It is important to note that the lifecycle of the structure pointed to by the pointer obtained from private_get is managed by the VideoFrame to which it belongs.

some example code snippet:

    #include <bmf/sdk/av_convertor.h>

    MediaDesc dp;
    auto yuvformat = hmp::PixelInfo(hmp::PF_YUV420P);
    auto src_vf = VideoFrame::make(640, 320, yuvformat);

    auto dst_vf = bmf_convert(src_vf, MediaDesc{}, dp);

    const AVFrame* frame = dst_vf.private_get<AVFrame>();
    EXPECT_EQ(frame->width, 1920);
    EXPECT_EQ(frame->height, 1080);
    EXPECT_EQ(frame->format, AV_PIX_FMT_RGB24);
AVFrame to VideoFrame
  1. use private_attach set AVFrame as private_data of VideoFrame
  2. src_dp set media_type with value MeidaType::kAVFrame
  3. use bmf_convert to convert
  4. get the return VideoFrame

some example code snippet:

    VideoFrame src_with_avf;
    MediaDesc src_dp;
    VideoFrame vf = bmf_convert(src_with_avf, src_dp, MediaDesc{});

Python Interface

The unified bmf_convert as C++ will be designed and implemented later.

Scale and colorspace conversion






Sample code:

    from bmf import *
    import bmf.hml.hmp as mp

    NV12 = mp.PixelInfo(mp.PixelFormat.kPF_NV12, mp.ColorSpace.kCS_BT470BG, mp.ColorRange.kCR_MPEG)
    RGB = mp.PixelInfo(mp.PixelFormat.kPF_RGB24, mp.ColorSpace.kCS_BT709, mp.ColorRange.kCR_MPEG)
    src_vf = pkt.get(VideoFrame)
    out_frame = mp.Frame(src_vf.frame().width(), src_vf.frame().height(), NV12, device='cuda')
    mp.img.rgb_to_yuv(out_vf.frame().data(), src_vf.frame().plane(0), NV12, mp.kNHWC)

Device memory transfer

Interface used:

VideoFrame.frame().device() gets the Device property

VideoFrame.cuda() moves the memory data on cuda memory

VideoFrame.cpu() moves the memory data on cpu memory

Sample code:

    from bmf import *
    import bmf.hml.hmp as mp
    vf = pkt.get(VideoFrame)
    if (vf.frame().device() == mp.Device('cpu')):
        vf = vf.cuda()

Conversion between VideoFrame and third-party data structure

In python API, those types of third-party data type are supported:

  • VideoFrame, which is the general class of video frame in BMF. And VideoFrame includes Frame as member
  • numpy
  • torch

bmf.hml.hmp.Frame.numpy converts a BMF Frame to numpy, and Frame can be included in VideoFrame


Sample code

    from bmf import *
    import numpy as np
    np1 = np.array(obj)
    rgb = mp.PixelInfo(mp.kPF_RGB24)
    frame = mp.Frame(mp.from_numpy(npa, rgb)
    vf = VideoFrame(frame) frame process
    np0 = vf.frame().plane(0).numpy()
    np1 = vf.frame().plane(1).numpy()
    np2 = vf.frame().plane(2).numpy()

For bellow interface, Torch Enabled BMF is needed by compile, please reference “Install” section.

bmf.hml.hmp.from_torch convert a torch into bmf Frame

bmf.hml.hmp.torch convert bmf Frame to torch

Sample code:

    from bmf import *
    import torch
    vf = pkt.get(VideoFrame)
    torch_data = vf.frame().data().torch()
    #...torch process
    from bmf import *
    import bmf.hml.hmp as mp
    import torch
    vf = pkt.get(VideoFrame)
    rgb = mp.PixelInfo(mp.kPF_RGB24)
    torch_vf = torch.from_dlpack(vf.reformat(rgb).frame().plane(0))
    #... process of torch
    RGB = mp.PixelInfo(mp.PixelFormat.kPF_RGB24, mp.ColorSpace.kCS_BT709, mp.ColorRange.kCR_MPEG)
    frame = mp.Frame(mp.from_torch(torch_vf.contiguous()), RGB)
    bmf_vframe = VideoFrame(frame)

Last modified February 19, 2024 : fix baidu statistics (daa0758)