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• FFMpeg - Extract embedded closed captions on Windows - Duplicated text in file

  16 juin 2017, par Busturdust

  I have an H264, AAC mpeg transport stream file that I am receiving from a DVR vendor service.

  Probing the file :

  

  As you can see, it appears the Closed Captions are embedded into the video itself.

  I am using a windows ffmpeg

  ffmpeg.exe -i MSNBC_Live_With_Stephanie_Ruhle1497618000 -f lavfi -i "movie=MSNBC_Live_with_stephanie_ruhle1497618000[out+subcc]" -c:s subrip  test.srt

  This gives me a valid SRT file with content

  However, when viewing the file content, it does not seem to be in synch with the output as seen in VLC Player (playing with subs).

  In VLC, subtitles look fine.
  In Extracted SRT file, the subtitles appear to duplicate certain text within the blocks. They also appear to have some HTML style tags that are being added tot he content.

  

  Is there a different strategy I should be using to do the extraction. Since it looks fine in VLC i assuming that the actual CC stream is valid.

  Thanks, I look forward to input.

  EDIT : There are also warnings that get printed while ffmpeg is working.

  

• Mix Audio tracks with offset in SOX

  4 août 2012, par Laramie

  From ASP.Net, I am using FFMPEG to convert flv files on a Flash Media Server to wavs that I need to mix into a single MP3 file. I originally attempted this entirely with FFMPEG but eventually gave up on the mixing step because I don't believe it it possible to combine audio only tracks into a single result file. I would love to be wrong.

  I am now using FFMPEG to access the FLV files and extract the audio track to wav so that SOX can mix them. The problem is that I must offset one of the audio tracks by a few seconds so that they are synchronized. Each file is one half of a conversation between a student and a teacher. For example teacher.wav might need to begin 3.3 seconds after student.wav. I can only figure out how to mix the files with SOX where both tracks begin at the same time.

  My best attempt at this point is :

  ffmpeg -y -i rtmp://server/appName/instance/student.flv -ac 1 student.wav 
  
  ffmpeg -y -i rtmp://server/appName/instance/teacher.flv -ac 1 teacher.wav 
  
  
  
  sox -m student.wav teacher.wav combined.mp3 splice 3.3

  These tools (FFMEG/SoX) were chosen based on my best research, but are not required. Any working solution would allow an ASP.Net service to input the two FMS flvs and create a combined MP3 using open-source or free tools.

  EDIT :
  I was able to offset the files using the delay switch in SOX.

  sox -M student.wav teacher.wav combined.mp3 delay 2.8

  I'm leaving the question open in case someone has a better approach than the combined FFMPEG/SOX solution.

• Video is too short in Avconv (ffmpeg) — but only when run as a crontab

  2 septembre 2016, par Dr. Paul Ruth

  I’m working on a PHP script that creates half-hour videos, combining a 30-minute MP3 with a still-frame background image, and then putting it on YouTube through the Google API. It works great except when I run it from a crontab, and I can’t figure out why.

  It uses a shell command to run the following.

  avconv -loop 1 -framerate 2 -i background.png -loglevel verbose -i audio.mp3 -c:v libx264 -preset medium -tune stillimage -vf scale=\"trunc(oh*a/2)*2:720\" -crf 18 -c:a copy -shortest -y -pix_fmt yuv420p output.mkv

  When I run it from my shell, it produces a video just as long as the 30 minute MP3. But if I run it from any kind of crontab, the result is just a fraction of the full length as it will stop at about 3 or 4 minutes.

  Typical output below for a failed result. What baffles me is that it’s not that the script is aborted, and it doesn’t seem to time out. Rather than stop, it keeps going and will upload the short, unfinished version to YouTube.

  I thought it might be a shell environment problem, missing some part of the $PATH or variables. But even when I import all the env and path settings, it does not seem to work.

  Is there some way to make sure the avconf (or ffmpeg) command continues all the way through and does not stop too early ?

  Typical output dump below from one of the times it fails : https://gist.github.com/anonymous/ecaa77037926821dba19e9db5ccb3a10

  (I used avconv because my host service claimed ffmpeg was deprecated and that I should use avconv instead. Could a library like PHP-FFMPEG be better for this ?)