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• Trying to save frames as colored image using Ffmpeg in C++

  2 septembre 2021, par Tolga

  I am new to FFmpeg and I am trying to save the video frames as colored images. I have achieved saving them as grayscale using Netpbm, however, I need to save the frames as colored. I have tried implementing the code in this link.

  


  However, I get an error :

  


  'Exception thrown at 0x00E1FC4F (swscale-5.dll) in VideoDecoding2.exe:
 0xC0000005: Access violation writing location 0xCCCCCCCC.'


  


  Is there any way to improve this code or another way to save frames as colored ?

  


  Here is my code below.

  


  

  • src_pix_fmt is AV_PIX_FMT_YUV420p.

  


  • dst_pix_fmt is AV_PIX_FMT_RGB24.

  


  


  src_pix_fmt = avcc->pix_fmt;

src_width = avcc->width;
src_height = avcc->height;

dst_width = src_width;
dst_height = src_height;

numBytes = av_image_get_buffer_size(dst_pix_fmt, dst_width, dst_height, 0);

buffer = (uint8_t*)av_malloc(numBytes);

if ((ret = av_image_alloc(src_data, src_linesize, src_width, src_height, src_pix_fmt, 16)) < 0)
{
    printf("Couldn't allocate source image.\n");
    return 0;
}

av_image_fill_arrays(frameRGB->data, frameRGB->linesize, buffer, dst_pix_fmt, dst_width, dst_height, 0);

while (av_read_frame(avfc, packet) >= 0)
{
    ret = avcodec_send_packet(avcc, packet);
    if (ret < 0)
    {
        printf("Packets could not supplied to decoder.\n");
        return -1;
    }

    ret = avcodec_receive_frame(avcc, frame);
    printf("%d", ret);

    if (packet->stream_index == videoStream)
    {
        sws_ctx = sws_getContext(src_width, src_height, src_pix_fmt,
            dst_width, dst_height, dst_pix_fmt,
            SWS_BILINEAR, NULL, NULL, NULL);

        if (!sws_ctx)
        {
            printf("Cannot create scale context for conversion\n"
                "fmt:%s s:%dx%d --> fmt:%s s:%dx%d\n",
                av_get_pix_fmt_name(src_pix_fmt), src_width, src_height,
                av_get_pix_fmt_name(dst_pix_fmt), dst_width, dst_height);
            return 0;
        }

        sws_scale(sws_ctx, (const uint8_t* const*)frame->data, frame->linesize, 0, frame->height, dst_data, dst_linesize);

        FILE* f;
        char szFilename[32];
        int y;

        snprintf(szFilename, sizeof(szFilename), "frame%d.ppm", avcc->frame_number);
        fopen_s(&f, szFilename, "wb");
        
        if (f == NULL)
        {
            printf("Couldn't open file.\n");
            return 0;
        }
        
        fprintf(f, "P6\n%d %d\n255\n", dst_width, dst_height);

        for (y = 0; y < dst_height; y++)
            fwrite(frameRGB->data[0] + y * frameRGB->linesize[0], 1, dst_width * 3, f);
        
        fclose(f);
    }
}


  


• How to record an HTML animation and save it as a video, in an automated manner in the backend

  14 mai 2022, par frizurd

  I need to record a webpage and save it as a video, in an automated manner, without human interaction.

  


  I am creating a NodeJS app that generates MP4 videos on the request of the user. The user provides an MP3 file, the app generates animated waveforms for the sound file on top of an illustration.

  


  What I came up with so far is a system that opens a generated web page in the backend, plays the audio file, and shows audio visualization for the audio file on an HTML canvas element. On top of another canvas with mainly static components, such as images, that do not animate. The system records this, the output will be a video file. Finally, I will merge the video file with the sound file to create the final file for the user.

  


  I came up with 2 possible solutions but both of them have problems which I am not able to solve at the moment.

  


  ---

  


  Solution #1

  


  Use a headless browser API such as Phantomjs or Puppeteer to snatch a screenshot x time every second and pipe it to FFmpeg.

  


  The problem

  


  The problem with this is that the process is not realtime. It would work fine if it's JUST an animation but mine is dependant on the audio file. The audio file will play-on during the render which results in a glitchy 1FPS-esque video.

  


  Possible solution ?

  


  Don't play the audio file live but convert the audio file into raw data. Animate the audio visualization based on the raw data instead.
Not sure how to do this and if it's even possible.

  


  ---

  


  Solution #2

  


  Play, record, and save the animation, all in the frontend.
Could use ccapture.js to record and save a canvas.
Use a headless browser to open the page and save it to disk when it's done playing.
Doesn't sound like it's the best solution.

  


  The problem(s)

  


  I have more than 1 canvas.
It takes a while, especially when the audio file is longer than 10 minutes.
Making users wait for a long time can be a deal-breaker.

  


  Possible solution ?

  


  Merge canvases into one.

  


  No idea how to speed up the rendering time and I doubt it's possible this way.

  


• record desktop save every 30 minutes

  31 mars 2014, par Maged E William

  here is my question that related to the same problem :

  better way to record desktop via ffmpeg

  I have this command : ffmpeg -f dshow -i video="screen-capture-recorder" -r 30 -t 10 E:\test01.flv

  And i am happy with it, but i wonder if i can make it save every 30 minutes so if the power went off i only loses the last 30 minutes.

  I use C# to launch and hide ffmpeg cmd, so i wonder how to make it save to the same test01.flv every 30 minutes ?