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• Some Java Process objects finish and close, but some finish and stall

  28 mars 2020, par brendanw36

  My program uses ProcessBuilder to make various calls to ffmpeg. My problem is that with certain commands I can create a Process, have it run, and when it is done it will terminate/exit/close itself and the program will end whereas other commands will run and create a finished output (in my case it will finish encoding a file with no corruption or anything at the end of the video), but won’t close at which point I need to force terminate the program. I have tested the ffmpeg commands that I am running in Windows Command Prompt and they all run fine without need for user input or anything. I will show some examples of commands that do and don’t work, but ultimately what I need is a way to tell why certain Processes do and don’t work. You probably don’t even need to read the rest of this post if you know the inner workings of the Process class better than I do.

  How I create my processes :

  ProcessBuilder pb = new ProcessBuilder(commandGoesHere);
  
  Process p = pb.start();
  
  p.waitFor();

  Works :
  ffmpeg -i test.y4m -f segment -segment_times timecodeList .temp/sgmnt_%d.y4m

  This command takes a y4m(raw video format/large file size/1.7 GB for 53s of 720p video) and cuts it in to chunks.

  Doesn’t work (sometimes) :
  ffmpeg -i chunkname.y4m outputName.mkv

  This command takes the chunked video and encodes it as h.264/AVC video. When I create a process with this command it only works if the chunk is small in which case the Process will start, do its work, and close.

  Doesn’t work ever :
  ffmpeg -i test.mkv -c:v copy -f segment -segment_times timecodeList .temp/sgmnt_%d.mkv

  This command takes and h.264/AVC input video and cut it in to chunks, but this one doesn’t terminate/exit/close when it’s done. I’m forced to terminate the program which I do after seeing the Process’s CPU utilization drop to 0% in Task Manager. When I force terminate the program and check the output folder, all the chunks are there and not corrupted so I know it finished running successfully.

• ffmpeg subtitle font size too big

  21 avril 2020, par Harry Vũ

  After making subtitles in Aegisub, I save it as .ass file, with font size set from style manager,
I used this command

  



  ffmpeg -i video.mp4 -b:v 1M -vf subtitles=subtitle.ass out.mp4


  



  but the output file has the font a few sizes too big, larger than the original size I set in Aegisub.
Did I do something wrong ?
This was the intended size :

  



  

  



  And this is the output size :

  



  

  



  Here's the ass file
ass file

  


• ffmpeg, how to extract single frame, 0.5 seconds before the end ? [duplicate]

  24 avril 2020, par Tonny

  I've got a bunch (several 100) of videos (all different frame-rates and different lengths).
  
Each has an end-title during the last second of the video, that shows some important information I need to check.
  
Playing each video in a player, scrolling to the end and trying to pause it in the last second is just to cumbersome/time-consuming.
  
Grabbing a frame at that position and saving it as an image for each video lets me quickly check the info using the image-preview in my file-manager. Which is much more efficient.

  



  ffmpeg can capture single frames and write them to a jpg or png, but I am at a loss how to extract a frame in the middle of that title sequence. 0.5 seconds before the end of each video would be the sweet spot. (There is a animation effect during that 1 second sequence that makes the text in the video sometimes hard to read, but exactly in the middle the visibility is best.)
  
As far as I can tell ffmpeg can't use offsets "from the end", so I assume ffprobe is probably needed to analyze the video and on basis off that the correct ffmpeg command can be generated.

  



  I can handle the scripting around it to batch-process all the files.
  
Problem is that I'm very unfamiliar with video in general, ffmpeg and ffprobe in particular. I need some help to get started.
  
If someone can explain to me how to get from the full video 'clip.mp4' to the single frame 0.5 seconds before the end in 'clip_frame.jpg' I would be most grateful.