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• Keep ffmpeg converting images to video when new images are incoming

  23 septembre 2019, par Jongseok Yoon

  Is there a way to keep ffmpeg convert images incoming to HLS, and stop whenever I want ?

  I’m using ffmpeg to convert images to m3u8/ts for streaming. A camera device will send images 24/7, and ffmpeg will convert those when users requested until they stop watching.

  For now, I get images from a camera device by Java network, then move those images to ffmpeg input directory and convert those with C++. It’s a loop that does this job, so new ffmpeg is executed every time images are moved.

  The problem is there are too many ts files leftover, and they’re taking a lot of spaces on server. So I tried to delete those with delete_segments option, but since ffmpeg is executed every time, it couldn’t delete segments made from ffmpeg right before it.

  Here are some ways I consider :

  1. To remove files with another function, without ffmpeg.
  2. Maybe transfer images directly to ffmpeg input, and somehow make ffmpeg keep convert those images to ts. (And I couldn’t think of somehow)
  3. Or maybe change the whole structure.

  It would be much easier with the option 1, but it would be great if I can do this with ffmpeg’s own functions.

• How can I display the frame got by FFmpeg cuvid decoder without copy to host memory ?

  21 septembre 2019, par hefty

  Nowadays I am working on a video display program using FFmpeg to decode the frames. For h264 input, I chose h264_cuvid to decode and get decoded AVFrame store in Nvidia video card’s device memory.
  
  Now I am using some inefficient way to display the frame by copying the hardware frame to host memory and then display :

  avcodec_receive_frame(decode_ctx, hw_frame); // Get decoded hardware frame that store in device memory.
  
  
  
  av_hwframe_transfer_data(sw_frame, hw_frame, flag); // Copy the hardware frame to the host memory.
  
  
  
  //...some code to scale and display the sw_frame.

  I want to display the hw_frame by Direct3D surface directly but I don’t know how to access the data in hw_frame and copy the pixel data to a D3D surface natively (without accessing the host memory).
  
  What I know is that the hw_frame’s data[0] and data[1] are CUdeviceptr pointing to the NV12 data store in device memory, anyone knows how to use the CUdeviceptr to transfer the data to a D3D surface through the device memory and display ?

• 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 ?