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• How to fix duration for an incompletely downloaded video ?

  15 octobre 2017, par Krash

  I am partially downloading a video by specifying the Ranges header. I am doing this in python. So, suppose there is video whose duration is 4:43 min and has size 2.56 mb and I am only downloading 1 mb of it, so the actual duration of the video is somewhere around the 2 min mark. Now when I play this video, it plays till it has downloaded but shows 4:43 still as its total duration and abruptly ends like a corrupted video file does. Is there a way I can edit the bytes I receive on downloading the file, so that the video player recognises the exact position after which it should end ?

  More importantly, I want to know if in videos, the start and end is determined by some set of bytes ? Like, if I download a video from the 3000th byte to 6000th byte, it won’t play as if its a corrupt video, so I want to know if its possible to add some bytes to the beginning of the file to let the player know that this is the beginning. How does a video player determine the end duration of a video from just the bytes ?

• ffmpeg tile screenshot file with uniform distribution over video length

  23 octobre 2017, par Michael Yousef

  I’m trying to take a video and create a screenshot file for it. I want it to cover the entire duration of the video and be uniformly distributed over the video. I have a command right now that I found online, it can produce a screenshot file, but it doesn’t cover the entire duration

  ffmpeg -ss 00:05:00 -i video.mp4 -frames 1 -vf "select=not(mod(n\,8000)),scale=320:240,tile=4x8" out.png

  Instead of having it cap every 80 seconds, I want it to determine what the duration is use that. It should cap the first screen at my initial offset, then however far ahead as necessary.

  Also, if anyone knows how to add information to the outputted file at the top, like filename, duration, bitrate, etc., that’s also something I want to output.

• How to set comma delimited values from stdout ?

  28 octobre 2017, par gregm

  I have a batch file that processes the output of an ffprobe query. It retrieves several bits of data that I use to determine some ffmpeg directives. In particular I’m converting h264 videos into h265 if the video frame height is 720 or greater. I also convert the audio stream to aac if it isn’t already and if that stream is higher than 128 kbps I convert it down to 128.

  I can do all of that by calling ffprobe a number of times and use if statements to decide what my ffmpeg command will be.

  I’d like my batch file to be more efficient so I was thinking that if I could take the output of one (maybe two) ffprobe queries and then stick that output into a for /f token=.... loop then I could set each ffprobe data point to a variable and then just check the variables to decide what the resulting ffmpeg command will be.

  Here’s what I have right now to simply check if the video stream is hevc. If it isn’t then ffmpeg converts the video to hevc and copies the audio to aac.

  for %%a in ("*.*") do (
  
  ffprobe -v quiet -show_entries stream=index,codec_name,height -of csv "%%a" 2>&1 | findstr "hevc"
  
  if errorlevel 1 (
  
      ffmpeg.exe -hwaccel cuvid -i "%%a" -pix_fmt p010le -c:v hevc_nvenc -preset slow -rc vbr_hq -b:v 4M -maxrate:v 10M -c:a aac "%%~na.h265-convert.mp4"
  
  ))

  That ffprobe query output looks like this :

  stream,0,h264,480

  I was thinking if I could tokenize that output with something like :

  for /f "tokens=1,2,3,4 delims= " %%a in ("______") do set codec=%%b&set fheight=%%d

  I don’t know what to put in the spot where I have the _______. I really don’t want to create a temp file unless that’s the only option though.

  1) Is this an efficient way to achieve what I’m trying to do ?

  2) What do I use where I have a blank line above ________ to call the output of the ffprobe query to use in my for loop ?