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• ffmpeg - Drawing rotated text on video with complex filters takes a very long time

  14 mai 2019, par Bedrule Paul

  I am trying to overlap different text pieces on some placeholders in a video, and I am using multiple complex filters of the following type :

  ffmpeg -i ~/Desktop/input.mp4 -filter_complex  \
  
      "color=black@0:100x100,format=yuva444p[c]; \
  
      [c][0]scale2ref[ct][mv31]; \
  
      [ct]setsar=1,split=1[t31];\
  
      [t31]\
  
      drawtext=text='text':x='main_w/2-text_w/2+70':y=210:fontsize="100":fontcolor=black,\
  
      drawtext=text='text2':x='main_w/2-text_w/2+75':y=340:fontsize="100":fontcolor=black,\
  
      rotate=-0.07:ow=rotw(-0.07):oh=roth(-0.07):c=black@0[txta31]; \
  
      [mv31][txta31]overlay=enable='between(t, 0, 1.15)':x='min(0,-H*sin(-0.07))':y='min(0,W*sin(-0.07))':shortest=1" \
  
         ~/Desktop/result.mp4 -y1

  My goal is to write differently rotated texts on different time intervals in the video. The problem is that at about 10-12 [t31]-like pieces(here is an example of only one command), the rendering time of the video is twice the time of the video, whereas drawing straight horizontal text takes about 10-20% of the total video length (examples, for a 1 minute video, it takes about 8-10 seconds to write straight horizontal text, and about 2 minutes to write the same amount of text, but inclined with an angle). Is there any better way to do these multiple rotated text bits with more performance ?

• How to set reset_timestamps with FFMPEG C/C++

  16 août 2017, par hung

  I save my RTSP stream to mp4 video file every minute. But the problem is when new video created, the start time is not close to 0, it increases continously, here’s out put of a video like that with ffprobe :

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './2017/8/15/8/56/56.mp4':
  
  Metadata:
  
  major_brand     : isom
  
  minor_version   : 512
  
  compatible_brands: isomiso2avc1mp41
  
  encoder         : Lavf57.41.100
  
  Duration: 00:01:00.28, start: 60.247005, bitrate: 2244 kb/s
  
  Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuvj420p(pc, bt709), 1280x720 [SAR 1:1 DAR 16:9], 2243 kb/s, 14.91 fps, 25 tbr, 15360 tbn, 30 tbc (default)
  
  Metadata:
  
    handler_name    : VideoHandler

  You can see the start value is 60.247005. When I use ffmpeg command line and add option ’reset_timestamps’ it work, all start value close to 0, and if i remove ’reset_timestamps’ it output videos like my code..Here’s command I use :

  ffmpeg -i rtsp://usr:pass@ipaddress/Streaming/Channels/1?tcp -c copy -map 0 -f segment -segment_time 20 -segment_format mp4 -reset_timestamps 1 "capture-%03d.mp4"

  So, I hope i can set the option reset_timestamps in my code, but it seem i can’t. I try with this but no luck :

  AVDictionary* opts = NULL;
  
  av_dict_set(&opts, "reset_timestamps", "1", 0);
  
  
  
  avformat_write_header(ofmt_ctx, &opts);

  Code was posted in my previous question : How to set start time of video saved from RTSP stream with FFMPEG

  Anyone knows how to do that ? Thanks.

• FFMPEG video encoding time increases over time

  8 août 2018, par NStof

  I am creating a fairly basic DVR in C# using the FFMPEG wrapper in Accord.net. Essentially it works by getting the raw frames from the on-board frame grabber, displays the frame on screen and places it in a buffer. In a Separate thread in 20 second intervals, the frames are taken from the buffer and using Accord.Video.FFMPEG.VideoFileWriter.WriteVideoFrame(Bitmap bmp) the frame is encoded and saved to disk. Video is saved in two minute file chunks.
  This works happily for about 24-30 hours, however after that it looks like the average time it takes to encode/save each frame increases to the point where it gets new frames faster than they can be saved. This causes buffer to grow and ends in tears.

  What I would like to know is why does the time it takes to complete the WriteVideoFrame(Bitmap bmp) function increase over time.

  What I think I know so far :
  I do not know if this problem is caused by something in FFMPEG or in the Accord.net wrapper.
  I am reasonably sure it is not caused by hardware. Neither CPU usage nor HDD are working particularly hard. In fact, when I monitor the CPU usage, it does not work any harder or less hard when the encoding time increases.
  When I stop recording (close and dispose all Accord.net objects) and start again, it does not reset the encoding speed. Only when I close the software and start it again does it fix the problem.
  Any thoughts and help with this will be greatly appreciated. If more information is required, please let me know.