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• ffmpeg C API - creating queue of frames

  25 mai 2016, par lupod

  I have created using the C API of ffmpeg a C++ application that reads frames from a file and writes them to a new file. Everything works fine, as long as I write immediately the frames to the output. In other words, the following structure of the program outputs the correct result (I put only the pseudocode for now, if needed I can also post some real snippets but the classes that I have created for handling the ffmpeg functionalities are quite large) :

  AVFrame* frame = av_frame_alloc();
  
  int got_frame;
  
  
  
  // readFrame returns 0 if file is ended, got frame = 1 if
  
  // a complete frame has been extracted
  
  while(readFrame(inputfile,frame, &got_frame)) {
  
    if (got_frame) {
  
      // I actually do some processing here
  
      writeFrame(outputfile,frame);
  
    }
  
  }
  
  av_frame_free(&frame);

  The next step has been to parallelize the application and, as a consequence, frames are not written immediately after they are read (I do not want to go into the details of the parallelization). In this case problems arise : there is some flickering in the output, as if some frames get repeated randomly. However, the number of frames and the duration of the output video remains correct.

  What I am trying to do now is to separate completely the reading from writing in the serial implementation in order to understand what is going on. I am creating a queue of pointers to frames :

  std::queue queue;
  
  int ret = 1, got_frame;
  
  while (ret) {
  
    AVFrame* frame = av_frame_alloc();
  
    ret = readFrame(inputfile,frame,&got_frame);
  
    if (got_frame) 
  
      queue.push(frame);
  
  }

  To write frames to the output file I do :

  while (!queue.empty()) {
  
    frame = queue.front();
  
    queue.pop();
  
    writeFrame(outputFile,frame);
  
    av_frame_free(&frame);
  
  }

  The result in this case is an output video with the correct duration and number of frames that is only a repetition of the last 3 (I think) frames of the video.

  My guess is that something might go wrong because of the fact that in the first case I use always the same memory location for reading frames, while in the second case I allocate many different frames.

  Any suggestions on what could be the problem ?

• Is there a way to change the ffplay playback speed while running

  20 mai 2024, par richjhart

  I am trying to modify ffplay 7.0 to allow us to modify the playback speed while running. Our use-case only involves basic video-only mp4 files.

  


  We can set the playback speed with something like the following :

  


  ffplay -i ..\Video\SampleVideoLong.mp4 -vf "setpts=5.0*PTS" -loglevel debug -sync video

  


  But I don't know how to change that option "live" (note if I don't choose -sync video, it gets very laggy - but that's fine as our use-case is video only.

  


  I have tried the following (with just a fixed rate at the moment) :

  


          {
            static double l_CurrentSpeed = 1.0;
            double l_NewSpeed = 2.0;
            double l_Diff = l_NewSpeed / l_CurrentSpeed;
            double l_ClockSpeed = cur_stream->extclk.speed;
            double l_NewClockSpeed = l_ClockSpeed * l_Diff;
            av_log(NULL, AV_LOG_DEBUG,
                "Changing speed from %f to %f\n",
                l_ClockSpeed, l_NewClockSpeed
                );

            set_clock_speed(&cur_stream->vidclk, l_NewClockSpeed);
            //set_clock(&cur_stream->vidclk, l_NewClockSpeed, cur_stream->extclk.serial);
            l_CurrentSpeed = l_NewSpeed;
        }


  


  I've set both the pts (set_clock()) and the "speed" (set_clock_speed()), but neither of these had any effect.

  


  Would I need to something extra, or is there a way to update the setpts expression in the video filter from ffplay ?

  


  Note the metadata of the file we are trying with is :

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '..\Video\SampleVideoLong.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf61.1.100
  Duration: 00:18:10.56, start: 0.160000, bitrate: 1755 kb/s
  Stream #0:0[0x1](und), 1, 1/90000: Video: mpeg2video (Main), 1 reference frame (mp4v / 0x7634706D), yuv420p(tv, bt709, progressive, left), 1920x1080 [SAR 1:1 DAR 16:9], 0/1, 1754 kb/s, 25 fps, 25 tbr, 90k tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : [0][0][0][0]
        encoder         : XDCAM EX 1080p25
      Side data:
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 278528 vbv_delay: N/A


  


  I believe the files we'll be using should have identical or similar metadata.

  


• mencoder. Encoding from multiple input image files compatible with web browser (No video support and MIME type) [duplicate]

  23 juin 2020, par iblasi

  I have multiple JPG files that I want to use to make a TimeLapse video compatible with the web browser to upload it on my web page.
Create a video with mencoder from multiple images is explained in some webpages such us here, that shows how to create a video.

  


  ls -Ltr my_Pics/*.jpg >files.txt
mencoder -nosound -ovc lavc -lavcopts vcodec=mpeg4 -o video.avi -mf type=jpeg:fps=4 mf://@files.txt


  


  The video is set with no sound and to have one picture every 250ms (4 fps).
These command lines create an AVI video that I can see correctly with the VLC video tool. However, if I try to open it in a web browser it shows an error :

  


  


  No Video with Supported Format and MIME type found

  


  


  So, based on other similar comments (as here), I tryed to use ffmpeg renaming all my files as ffmpeg requires a number serial format. But it happens the same, that I can see it in VLC but not in the browser.

  


  ffmpeg -r 4 -i ./output/%04d.jpg -vcodec libx264 video.mp4


  


  Based on research made on internet I am quite sure that it is due the the encoding and/or container. I tryed multiple options of codecs nd containers existing on documentation (here) but still not able to find a way to work.

  


  If, once I create the video, I use the VLC tool to manually convert the video to ".m4v" I was able to create a video that the web browser recognizes. But I would like to do it with command lines to automate it.