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• FFMPEG map 7.1 surround to 5.1 during transcode

  12 décembre 2022, par dongle

  I have a ProRes MOV whose audio contains 8 channels of audio in a 7.1 surround layout (L R C LFE Ls Rs Lt RT).

  


  I am preparing an H.264 MP4 for a media player that only supports AAC, and does not support 7.1, so I would like to map to 5.1, dropping ther 7th and 8th channels (Lt and Rt). Under normal circumstances I would just use the below for my transcode :

  


  ffmpeg -i input_file -c:v libx264 -pix_fmt yuv420p -preset veryslow -crf 18 -c:a aac output_file

  


  I've been looking at the documentation for audio layout manipulation, but am having trouble wrapping my head around it and they don't have a specific example of what I'm trying to do.

  


  Do I need to export my audio to a WAV file first, or is there a way to manage the mapping in my transcode command ? How can I map the existing first 6 channels to the new file ?

  


• Streaming with ffmpeg

  15 juillet 2014, par jakebird451

  I am using ffmpeg to encode a video from a non-mp4 format to an mp4 format. My goal is to provide the video while its encoding to the client (http link). The link is provided with cherrpypy using python. To perform the encoding, I use the subprocess.Popen command and redirect the output to a pipe. Providing the file live to a browser is fine, however finding how to encode the video though ffmpeg to get my desired result is not going so well.

  The only command I found so far that even works is : ffmpeg -i {inputfile} -nostats -frag_duration 3600 -f mp4 -. This command "works", the audio is flawless however the video is encoded to what looks like 4x (or 2x) the speed of the original video. So I have been experimenting with commands to see if I can fix the video defect but so far I have yet to fix the same problem. I have been attempting to inject the -vcodec libx264 command, still the same problem.

  To assist in troubleshooting my problem, I decided to also save the stream to a file. Playing the recorded file yields the same effect. However, interestingly enough, playing the video though VLC and Windows Media Player fixes the video problem and the video plays perfectly fine. Sound and all. It just seems as though the html5 player (with Google Chrome) does not like however I am packing the video. It seems as thought Google Chrome and my encoded file do not play well together.

  Continuing with the streaming issue, breaking the encoding process still shows the video encoding just fine in VLC and in Windows Media Player. Well, it plays the video just fine up to until I pressed ctrl-c of course. So it seems that maybe it is not the encoding that is the problem, but either :

  1. It is a problem with the header for the generated mp4 file
  2. Google Chome is disregarding the frame rate specified in the file and mandating, say, 60 fps or even 120 ? (which would cause the fast forwarding effect)

  The webpage that I am using to show the video is dynamically created and is formed using the template below :

      
  
          
  
      
  
      
  
          <video controls="controls">
  
              <source src="{link}"></source>
  
              Your browser sux. Fix it.
  
          </video>
  
      

  The {title} and {link} components are substituted with the corresponding components. If anyone has any suggestions on how to troubleshoot this problem I would be more than willing to listen. As of right now, I am stuck on how to progress with the current state of this issue.

• How to burn colorful subtitle into video using ffmpeg ?

  17 juin 2014, par qliq

  I want to burn an srt file into a mp4 video. To make the subtitles perfectly visible, I want the subtitle text to be yellow on a brownish semi-transparent background.

  I know that there are some GUI tools like Arista Transcoder but it does not allow color manipulation. I also know that ffmpeg make these manipulations possible but the gazillion flags on the docs are over the top of my head.

  So I appreciate a ready made ffmpeg command to do so.