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• Display FFMPEG decoded frame in a GLFW window

  17 juin 2020, par Infecto

  I am implementing the client program of a game where the server sends encoded frames of the game to the client (via UDP), while the client decodes them (via FFMPEG) and displays them in a GLFW window. 
My program has two threads :

  



  

  1. Thread 1 : renders the content of the uint8_t* variable dataToRender

  


  2. Thread 2 : keeps obtaining frames from the server, decodes them and updates dataToRender accordingly

  


  



  Thread 1 does the typical rendering of a GLFW window in a while-loop. I have already tried to display some dummy frame data (a completely red frame) and it worked :

  



  while (!glfwWindowShouldClose(window)) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    ...

    glBindTexture(GL_TEXTURE_2D, tex_handle);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, window_width, window_height, 0, GL_RGB, GL_UNSIGNED_BYTE, dataToRender);
    ...
    glfwSwapBuffers(window);
}


  



  Thread 2 is where I am having trouble. I am unable to properly store the decoded frame into my dataToRender variable. On top if it, the frame data is originally in YUV format and needs to be converted to RGB. I use FFMPEG's sws_scale for that, which also gives me a bad dst image pointers error output in the console. Here's the code snippet responsible for that part :

  



          size_t data_size = frameBuffer.size();  // frameBuffer is a std::vector where I accumulate the frame data chunks
        uint8_t* data = frameBuffer.data();  // convert the vector to a pointer
        picture->format = AV_PIX_FMT_RGB24;
        av_frame_get_buffer(picture, 1);
        while (data_size > 0) {
            int ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
                data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
            if (ret < 0) {
                fprintf(stderr, "Error while parsing\n");
                exit(1);
            }
            data += ret;
            data_size -= ret;

            if (pkt->size) {
                swsContext = sws_getContext(
                    c->width, c->height,
                    AV_PIX_FMT_YUV420P, c->width, c->height,
                    AV_PIX_FMT_RGB24, SWS_BILINEAR, NULL, NULL, NULL
                );
                uint8_t* rgb24[1] = { data };
                int rgb24_stride[1] = { 3 * c->width };
                sws_scale(swsContext, rgb24, rgb24_stride, 0, c->height, picture->data, picture->linesize);

                decode(c, picture, pkt, outname);
                // TODO: copy content of picture->data[0] to "dataToRender" maybe?
            }
        }


  



  I have already tried doing another sws_scale to copy the content to dataToRender and I cannot get rid of the bad dst image pointers error. Any advice or solution to the problem would be greatly appreciated as I have been stuck for days on this.

  


• Set "start" field to 0 in mp3 with ffmpeg

  11 juin 2020, par TomatoCo

  I'm trying to change the bitrate and sample rate of an MP3 to match another to try and stop a small audio glitch from occurring when some game tries to play it. I've got the sample rate and bitrate right where I want them, but I can't get the "start" portion of

  



    Duration: 00:03:33.81, start: 0.025057, bitrate: 196 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 196 kb/s


  



  to go to 0, like the mp3 I'm trying to replace. The target looks like :

  



    Duration: 00:06:47.59, start: 0.000000, bitrate: 196 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, stereo, fltp, 196 kb/s


  



  I've tried a variety of silenceremove filters and -ss flags to try and trim it, but I can't get rid of that "start" field. Google is failing me. What args am I looking for ?

  


• FFMPEG : How to extract a PNG sequence from a video, remove duplicate frames in the process and keep the original frame number ?

  16 mai 2020, par Simon

  I have a recording of an old game which has variable framerate. Since I want to process individual frames to upscale and modernize the footage I would like to avoid any duplicate frames. I know that I can use this function to extract all frames from a video :

  



  ffmpeg -i input.mov -r 60/1 out%04d.png


  



  And I know that I can remove duplicate frames using this function :

  



  ffmpeg -i input.mov -vf mpdecimate,setpts=N/FRAME_RATE/TB output.mov


  



  However, the above command removes duplicate frames and puts frames next to each other whereas in order to keep a timecode of sorts it would be a lot more useful to be able to extract PNGs with frame number (video is progressive 60fps) but without all of the duplicates.

  



  So, the question is : what if I want to extract PNG files BUT maintain the original corresponding framenumber within the sequence ? So, if we have a video with 10 frames and frames 2-8 are duplicates it spits out 1.png 2.png 9.png and 10.png ? How do I combine both bits of code listed above ?