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• How to Capture/Convert video using VLC or FFmpeg starting at the next encountered I-Frame

  28 juillet 2014, par DavidG

  I am capturing multicast video using VLC.exe and performing some processing/converting using FFmpeg.exe. The resulting video starts with a gray background with some of the moving objects moving through the gray background. This seems to me that the video is not starting on an I-Frame, but on a B-Frame or a P-Frame. However, when I run ffprobe, it states the first frame is a key frame. After about 1/2 second, the video plays fine.

  Here is the command I’m using to capture the video :

  vlc.exe -I curses --run-time=10 "my.sdp" --sout=video.mp4

  I’m not using anything special when I convert to an mp4 file using FFmpeg :

  ffmpeg.exe -i video.mp4 -s 400x300 final.mp4

  I tried to post an image of the first frame or two, but Stackoverflow gave me an error stating I need at least 10 reputation to post images. Sorry about that, an image would have helped.

  I ran the command "ffprobe show_frames " and it looks like the first frame is a key frame. Of course I’m new to all this and I don’t know what I’m doing or seeing.

  Here is beginning of the output to the "ffprobe show_frames " command :

  [FRAME]
  
  media_type=video
  
  key_frame=1
  
  pkt_pts=0
  
  pkt_pts_time=0.000000
  
  pkt_dts=0
  
  pkt_dts_time=0.000000
  
  pkt_duration=1001
  
  pkt_duration_time=0.033367
  
  pkt_pos=48
  
  pkt_size=756
  
  width=400
  
  height=300
  
  pix_fmt=yuv420p
  
  sample_aspect_ratio=1:1
  
  pict_type=I
  
  coded_picture_number=0
  
  display_picture_number=0
  
  interlaced_frame=0
  
  top_field_first=0
  
  repeat_pict=0
  
  reference=3
  
  [/FRAME]

  Is there any way to either tell VLC.exe to start capturing on an I-Frame (This would be the best solution as I specify a duration to capture the video) or is there a way to tell FFmpeg.exe to start converting the input video starting at the first I-Frame encountered ?

  Thanks,
   David

• 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 merge multiple audio files together with ffmpeg lib ?

  23 novembre 2022, par itsMU1X

  I have many audio files, and I want to merge them, but each audio file plays at a specific time, and the duration between them is in silent sound, and I specify the duration, as if I am making a timeline in the ffmpeg library
how can i do this ?