How to view/save AVFrame have format AV_PIX_FMT_YUVJ420P to file

Question

I have a AVFrame and I want to save it to file. If I only store frame->data[0] to file, the image will be Grey image, how to view full color? I use C language.

Do you have any suggestions on what I should read to understand and do these things by myself?

Use SwsContext and sws_scale to convert it from YUV to RGB – SuRGeoNix Feb 11 '22 at 12:05 — SuRGeoNix, Feb 11 '22 at 12:05

score 3 · Accepted Answer · answered Feb 11 '22 at 10:25

A relatively simple way to save and view the image is writing Y, U and V (planar) data to binary file, and using FFmpeg CLI to convert the binary file to RGB.

Some background:

yuvj420p in FFmpeg (libav) terminology applies YUV420 "full range" format.
I suppose the j in yuvj comes from JPEG - JPEG images uses "full range" YUV420 format.

Most of the video files use "limited range" (or TV range) YUV format.

In "limited range", Y range is [16, 235], U range is [16, 240] and V range is [0, 240].
In "full range", Y range is [0, 255], U range is [0, 255] and V range is [0, 255].

yuvj420p is deprecated, and supposed to be marked using yuv420p combined with dst_range 1 (or src_range 1) in FFmpeg CLI. I never looked for a way to define "full range" in C.

yuvj420p in FFmpeg (libav) applies "planar" format.
Separate planes for Y channel, for U channel and for V channel.
Y plane is given in full resolution, and U, V are down-scaled by a factor of x2 in each axis.

Illustration:

Y - data[0]:  YYYYYYYYYYYY
              YYYYYYYYYYYY
              YYYYYYYYYYYY
              YYYYYYYYYYYY
            
U - data[1]:  UUUUUU
              UUUUUU
              UUUUUU

V - data[2]:  VVVVVV
              VVVVVV
              VVVVVV

In C, each "plane" is stored in a separate buffer in memory.
When writing the data to a binary file, we may simply write the buffers to the file one after the other.

For demonstration, I am reusing my following answer.

I copied and paste the complete answer, and replaced YUV420 with YUVJ420.

In the example, the input format is NV12 (and I kept it). The input format is irrelevant (you may ignore it) - only the output format is relevant for your question.

I have created a "self contained" code sample that demonstrates the conversion from NV12 to YUV420 (yuvj420p) using sws_scale.

Start by building synthetic input frame using FFmpeg (command line tool).
The command creates 320x240 video frame in raw NV12 format:

    ffmpeg -y -f lavfi -i testsrc=size=320x240:rate=1 -vcodec rawvideo -pix_fmt nv12 -frames 1 -f rawvideo nv12_image.bin

The next code sample applies the following stages:

Allocate memory for the source frame (in NV12 format).
Read NV12 data from binary file (for testing).
Allocate memory for the destination frame (in YUV420 / yuvj420 format).
Apply color space conversion (using sws_scale).
Write the converted YUV420 (yuvj420) data to binary file (for testing).

Here is the complete code:

//Use extern "C", because the code is built as C++ (cpp file) and not C.
extern "C"
{
#include <libswscale/swscale.h>
#include <libavformat/avformat.h>
#include <libswresample/swresample.h>
#include <libavutil/pixdesc.h>
#include <libavutil/imgutils.h>
}


int main()
{
    int width = 320;
    int height = 240;   //The code sample assumes height is even.
    int align = 0;
    AVPixelFormat srcPxlFormat = AV_PIX_FMT_NV12;
    AVPixelFormat dstPxlFormat = AV_PIX_FMT_YUVJ420P;
    int sts;

    //Source frame allocation
    ////////////////////////////////////////////////////////////////////////////
    AVFrame* pNV12Frame = av_frame_alloc();

    pNV12Frame->format = srcPxlFormat;
    pNV12Frame->width = width;
    pNV12Frame->height = height;

    sts = av_frame_get_buffer(pNV12Frame, align);

    if (sts < 0)
    {
        return -1;  //Error!
    }
    ////////////////////////////////////////////////////////////////////////////


    //Read NV12 data from binary file (for testing)
    ////////////////////////////////////////////////////////////////////////////
    //Use FFmpeg for building raw NV12 image (used as input).
    //ffmpeg -y -f lavfi -i testsrc=size=320x240:rate=1 -vcodec rawvideo -pix_fmt nv12 -frames 1 -f rawvideo nv12_image.bin

    FILE* f = fopen("nv12_image.bin", "rb");

    if (f == NULL)
    {
        return -1;  //Error!
    }

    //Read Y channel from nv12_image.bin (Y channel size is width x height).
    //Reading row by row is required in rare cases when pNV12Frame->linesize[0] != width
    uint8_t* Y = pNV12Frame->data[0];   //Pointer to Y color channel of the NV12 frame.
    for (int row = 0; row < height; row++)
    {
        fread(Y + (uintptr_t)row * pNV12Frame->linesize[0], 1, width, f); //Read row (width pixels) to Y0.
    }

    //Read UV channel from nv12_image.bin (UV channel size is width x height/2).
    uint8_t* UV = pNV12Frame->data[1];   //Pointer to UV color channels of the NV12 frame (ordered as UVUVUVUV...).
    for (int row = 0; row < height / 2; row++)
    {
        fread(UV + (uintptr_t)row * pNV12Frame->linesize[1], 1, width, f); //Read row (width pixels) to UV0.
    }

    fclose(f);
    ////////////////////////////////////////////////////////////////////////////



    //Destination frame allocation
    ////////////////////////////////////////////////////////////////////////////
    AVFrame* pYUV420Frame = av_frame_alloc();

    pYUV420Frame->format = dstPxlFormat;
    pYUV420Frame->width = width;
    pYUV420Frame->height = height;

    sts = av_frame_get_buffer(pYUV420Frame, align);

    if (sts < 0)
    {
        return -1;  //Error!
    }
    ////////////////////////////////////////////////////////////////////////////


    //Color space conversion
    ////////////////////////////////////////////////////////////////////////////
    SwsContext* sws_context = sws_getContext(width,
        height,
        srcPxlFormat,
        width,
        height,
        dstPxlFormat,
        SWS_FAST_BILINEAR,
        NULL,
        NULL,
        NULL);

    if (sws_context == NULL)
    {
        return -1;  //Error!
    }

    sts = sws_scale(sws_context, //struct SwsContext* c,
        pNV12Frame->data,        //const uint8_t* const srcSlice[],
        pNV12Frame->linesize,    //const int srcStride[],
        0,                       //int srcSliceY, 
        pNV12Frame->height,      //int srcSliceH,
        pYUV420Frame->data,      //uint8_t* const dst[], 
        pYUV420Frame->linesize); //const int dstStride[]);    

    if (sts != pYUV420Frame->height)
    {
        return -1;  //Error!
    }
    ////////////////////////////////////////////////////////////////////////////


    //Write YUV420 (yuvj420p) data to binary file (for testing)
    ////////////////////////////////////////////////////////////////////////////
    //Use FFmpeg for converting the binary image to PNG after saving the data.
    //ffmpeg -y -f rawvideo -video_size 320x240 -pixel_format yuvj420p -i yuvj420_image.bin -pix_fmt rgb24 rgb_image.png

    f = fopen("yuvj420_image.bin", "wb");

    if (f == NULL)
    {
        return -1;  //Error!
    }

    //Write Y channel to yuvj420_image.bin (Y channel size is width x height).
    //Writing row by row is required in rare cases when pYUV420Frame->linesize[0] != width
    Y = pYUV420Frame->data[0];   //Pointer to Y color channel of the YUV420 frame.
    for (int row = 0; row < height; row++)
    {
        fwrite(Y + (uintptr_t)row * pYUV420Frame->linesize[0], 1, width, f); //Write row (width pixels) to file.
    }

    //Write U channel to yuvj420_image.bin (U channel size is width/2 x height/2).
    uint8_t* U = pYUV420Frame->data[1];   //Pointer to U color channels of the YUV420 frame.
    for (int row = 0; row < height / 2; row++)
    {
        fwrite(U + (uintptr_t)row * pYUV420Frame->linesize[1], 1, width / 2, f); //Write row (width/2 pixels) to file.
    }

    //Write V channel to yuv420_image.bin (V channel size is width/2 x height/2).
    uint8_t* V = pYUV420Frame->data[2];   //Pointer to V color channels of the YUV420 frame.
    for (int row = 0; row < height / 2; row++)
    {
        fwrite(V + (uintptr_t)row * pYUV420Frame->linesize[2], 1, width / 2, f); //Write row (width/2 pixels) to file.
    }

    fclose(f);
    ////////////////////////////////////////////////////////////////////////////


    //Cleanup
    ////////////////////////////////////////////////////////////////////////////
    sws_freeContext(sws_context);
    av_frame_free(&pYUV420Frame);
    av_frame_free(&pNV12Frame);
    ////////////////////////////////////////////////////////////////////////////

    return 0;
}

The execution shows a warning message (that we may ignore):

[swscaler @ 000002a19227e640] deprecated pixel format used, make sure you did set range correctly

For viewing the output as colored image:

After executing the code, execute FFmpeg (command line tool).
The following command converts the raw binary frame (in YUV420 / yuvj420p format) to PNG (in RGB format).

    ffmpeg -y -f rawvideo -video_size 320x240 -pixel_format yuvj420p -i yuvj420_image.bin -pix_fmt rgb24 rgb_image.png

Sample output (after converting from yuvj420p to PNG image file format):

This should be a little explainer post so I can bookmark easily :) — syntheticgio, May 27 '22 at 15:35

score 2 · Answer 2 · answered Feb 10 '22 at 10:25

2

AV_PIX_FMT_YUVJ420P is a planar format. data[0] is just a Y frame (grayscale), for the full image with the color you need to take into consideration: data[1] and data[2] for the U and V part of the frame respectively.

And it seems this format (AV_PIX_FMT_YUVJ420P) is deprecated in favor of the more common AV_PIX_FMT_YUV420P format, use this if it's up to you.

answered Feb 10 '22 at 10:25

the kamilz

1,860
1
15
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Do you have recommendations to read? I have tried some searches on these formats but found nothing. – Che Huu Feb 11 '22 at 09:14
With a quick search, I found this: https://www.emva.org/wp-content/uploads/GenICam_PFNC_2_1.pdf – the kamilz May 31 '22 at 13:58

boytjmjler · Answer 3 · 2022-07-30T08:59:36.210

You must convert to AV_PIX_FMT_BGRA

AVFrame* frameYUV; //frame YUVJ420P
AVFrame* frameGRB = av_frame_alloc();
frameGRB->width = frameYUV->width;
frameGRB->height= frameYUV->height;
frameGRB->format = AV_PIX_FMT_BGRA;
av_frame_get_buffer(frameGRB, 0);

SwsContext *sws_context = sws_getContext(frameYUV->width, frameYUV->height, AV_PIX_FMT_YUVJ420P, frameGRB->width, frameGRB->height, AV_PIX_FMT_BGRA, SWS_BICUBIC, NULL, NULL, NULL);
if (sws_context != NULL){
    sws_scale(sws_context, frameYUV->data, frameYUV->linesize, 0, frameYUV->height, frameGRB->data, frameGRB->linesize);
}

Array pixel is:

void* imageBuff = (void*)frameGRB->data[0];

Save file image:

HANDLE hFileBmp = CreateFile(szFilePath, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFileBmp != INVALID_HANDLE_VALUE) {
    int iWidth = frameGRB->width, iHeight = frameGRB->height;
    BITMAPINFOHEADER BitmapInfoHeader;
    ZeroMemory(&BitmapInfoHeader, sizeof(BitmapInfoHeader));
    BitmapInfoHeader.biSize = sizeof(BITMAPINFOHEADER);
    BitmapInfoHeader.biWidth = iWidth;
    BitmapInfoHeader.biHeight = -iHeight;
    BitmapInfoHeader.biPlanes = 1;
    BitmapInfoHeader.biBitCount = 32;
    BitmapInfoHeader.biCompression = BI_RGB;

    BITMAPFILEHEADER BitmapFileHeader;
    ZeroMemory(&BitmapFileHeader, sizeof(BitmapFileHeader));
    BitmapFileHeader.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
    DWORD dwBitmapSize = iWidth * 4 * iHeight;
    BitmapFileHeader.bfSize = dwBitmapSize + BitmapFileHeader.bfOffBits;
    BitmapFileHeader.bfType = 0x4D42; //BM

    DWORD dwBytesWritten = 0;
    if (WriteFile(hFileBmp, &BitmapFileHeader, sizeof(BitmapFileHeader), &dwBytesWritten, NULL) == TRUE) {
        if (WriteFile(hFileBmp, &BitmapInfoHeader, sizeof(BitmapInfoHeader), &dwBytesWritten, NULL) == TRUE) {
            WriteFile(hFileBmp, imageBuff, dwBitmapSize, &dwBytesWritten, NULL);
        }
    }
    CloseHandle(hFileBmp);
}

How to view/save AVFrame have format AV_PIX_FMT_YUVJ420P to file

3 Answers3