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• FFMPEG API : How to clear real-time buffer ?

  29 novembre 2018, par user67

  Here’s the c++ code that I’m using to access my webcam.

  int Camera::Init(char* file_name,
  
                  char* device_name,
  
                  char* format,
  
                  char* resolution,
  
                  char* frame_rate,
  
                  char* pixel_format)
  
  {
  
      av_log(NULL, AV_LOG_INFO, "---INIT STARTED\n");
  
      avdevice_register_all();
  
      av_register_all();
  
  
  
      AVDictionary* properties_collection = NULL;
  
      av_dict_set(&properties_collection, "f", format, NULL);
  
      av_dict_set(&properties_collection, "video_size", resolution, NULL);
  
      av_dict_set(&properties_collection, "framerate", frame_rate, NULL);
  
      av_dict_set(&properties_collection, "pix_fmt", pixel_format, NULL);
  
      AVInputFormat *input_format = av_find_input_format("dshow");
  
      char command_line[256];
  
      sprintf(command_line, "video=%s", device_name);
  
      AVFormatContext *input_context = avformat_alloc_context();
  
      //input_context->flags |= AVFMT_FLAG_NOBUFFER;      //DOESN'T HELP
  
      //input_context->max_picture_buffer = 0;            //ERR
  
  
  
      int err_code = 0;
  
      err_code = avformat_open_input(&input_context,
  
                                      command_line,
  
                                      input_format,
  
                                      &properties_collection);
  
      int i = 0;
  
      while (i++ < 30)
  
      {
  
          Sleep(1000);
  
          //avformat_flush(input_context); //DOESN'T HELP
  
          //av_free(input_context); //ERR
  
      }
  
      system("pause");
  
      return 0;
  
  }

  Right after "avformat_open_input()" it starts reading frames to some internal buffer without me even calling "av_read_frame()".
  After about 10 seconds it start’s giving me error messages :

  [dshow @ 0014ed40] real-time buffer [VirtualBox Webcam - FULL HD 1080P Webcam] [video input] 
  
  too full or near too full (62% of size: 3041280 [rtbufsize parameter])! 
  
  frame dropped!
  
  ...
  
  ...
  
  ...
  
  [dshow @ 0014ed40] real-time buffer [VirtualBox Webcam - FULL HD 1080P Webcam] [video input] 
  
  too full or near too full (100% of size: 3041280 [rtbufsize parameter])! 
  
  frame dropped!

  How to clear this buffer or avoid using it ?

  Thanks in advance.

  P.S.Please pardon my english.

  P.P.S.Have a good day.

• ffmpeg : two videos side-by-side with audio1 lang=ger & audio2 lang=eng

  19 janvier 2023, par miridigital

  I have two videos from two GoPro cameras. Both videos are rendered via ffmpeg side-by-side into a single video (left and right) and the audio is currently combined/mixed into two channels (stereo). I can hear both camera audio channels at the same time.

  


  Two channels stereo :

  


  ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "[0:v][1:v]hstack=inputs=2[v]; [0:a][1:a]amerge[a]" -map "[v]" -map "[a]" -ac 2 side-by-side.mp4


  


  audio from both videos mixed into a single file with 2 channels - mediainfo

  


  Now I want to switch between the two audio channels (cam1 or cam2) while I'm playing the side-by-side video.

  


  My first try : With four channels (without -ac 2 parameter) :

  


  ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "[0:v][1:v]hstack=inputs=2[v]; [0:a][1:a]amerge[a]" -map "[v]" -map "[a]" side-by-side.mp4


  


  audio from both videos mixed into a single file with 4 channels - mediainfo

  


  But the most video players can't easily select the channels 1+2 or 3+4 while playing.

  


  So I tried two languages :

  


  ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex "[0:v][1:v]hstack=inputs=2[v]; [0:a][1:a]amerge[a]" -map "[v]" -map "[a]" -metadata:s:a:0 language=ger -metadata:s:a:1 language=eng side-by-side.mp4


  


  audio from both videos mixed into a single file with 4 channels with languages - mediainfo

  


  But that's wrong. I can only see german with 4 channels. How can I put channels 1+2 into german and channels 3+4 into english ? Afterwards I should be able to use the multi language feature from most video players to switch the audio between cameras.

  


  Thank you,
  
Miriam

  


• Dynamic subtitles by ffmpeg

  8 septembre 2019, par Saeron Meng

  I would like to add some commentary texts into my video but I do not know how to use ffmpeg to realize this. The comments are like screen bullets through the screen, appearing in the right margin, moving and scrolling, and disappearing from the left.

  My thought is to count the length of the comments and define speeds for them to move and I have already gotten the comments saved as an xml file. But even though I can transfer it into srt file, the tricky problem is, it is hard to write the speeds of the subtitles, or something like that, in an srt file, and apply them to ffmpeg commands or APIs. Here is an example of comments (xml file) :

  <chat timestamp="671.195">
  
      <ems utctime="1562584080" sender="Bill">
  
          <richtext></richtext>
  
      </ems>
  
  </chat>
  
  <chat timestamp="677.798">
  
      <ems utctime="1562584086" sender="Jack">
  
          <richtext></richtext>
  
      </ems>
  
  </chat>

  The final result is like this (I did not find an example in websites in English. In China, such moving subtitles are called "danmu" or "screen bullets"), these colorful characters can move horizontally from right to left :

  

  1. I have searched some solutions on the Internet, most of which talk about how to write ass/srt files and add motionless subtitles. Like this :

  ffmpeg -i infile.mp4 -i infile.srt -c copy -c:s mov_text outfile.mp4

  3
  
  00:00:39,770 --> 00:00:41,880
  
  When I was lying there in the VA hospital ...
  
  
  
  4
  
  00:00:42,550 --> 00:00:44,690
  
  ... with a big hole blown through the middle of my life,
  
  
  
  5
  
  00:00:45,590 --> 00:00:48,120
  
  ... I started having these dreams of flying.

  But I need another kind of "subtitles" which can move.

  2. When it comes to scrolling subtitles, there are still some solutions : Scrolling from RIGHT to LEFT in ffmpeg / drawtext

  So my question is, how to combine the solutions above to arrange subtitles from top to bottom and let them move concerning the timestamps of the comments ?