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• Decode H.264 stream from live555 using ffmpeg

  3 septembre 2013, par Straticiuc Vicu

  I try to decode H.264 frames for an IP Camera that uses onvif. For this i am using example testRTSPClient from live555. In FAQ is said that function afterGettingFrame() is called every time a new packet came in buffer and that packet is an NAL unit. On live555 part everything looks good. Now for decoding i am using ffmpeg and the frame i pass to the decoder are formed like discribed Here. Now my problem is that the ffmpeg is unable to decode my frames and i am getting errors like :

  top block unavailable for requested intra4x4 mode -1 at 18 0
  
  error while decoding MB 18 0
  
  no picture 
  
  P sub_mb_type 13 out of range at 2 3

  What am i doing wrong with ffmpeg ?

  PS. example of I-Frame passed to ffmpeg Here

   with:
  
   red   is startcode
  
   green is SPS info
  
   black is PPS info 
  
   blue  is I-Frame delivered by live555

• FFmpeg pass arguments in a text file

  30 novembre 2023, par yazanpro

  I'm trying to get around the 32767 characters limit regarding the command line length in Windows (sometimes it's less than that). I have a large number of boxes that I'm trying to draw on a video. Typically I can concatenate the draw commands using a comma (,) like so (the following command draws two boxes) :

  



  ffmpeg -i input.mp4 -vf "drawbox=enable='between(t, 1.5, 4)' : x=100 : y=100 : w=200 : h=200 : color=green,drawbox=enable='between(t, 9, 18)' : x=500 : y=10 : w=150 : h=150 : color=red" -codec:a copy output.mp4


  



  However since I have many boxes to draw, the length of the entire command becomes too large.

  



  Does FFmpeg offer a way to pass all arguments in a text file instead of literal text ? Something like this :

  



  ffmpeg content(ffmpegCmd.txt)


  



  If that's not possible, is it possible to "buffer" the arguments into separate commands while exporting the result only in the last command ?

  


• ffmpeg moving text but only within Y limits

  28 décembre 2022, par Yoav Mor

  I need to add text to a video that will scroll from bottom to top ; I managed to do it with something similar to this :

  


  ffmpeg -i vid.mp4 -vf "drawtext=fontfile=tahoma.ttf:fontsize=20:fontcolor=green:x=(w-text_w)/2+20:y=if(lt(t\,2)\,480\,(h-400-(40*t))):textfile=scroll.txt:bordercolor=white:borderw=1" -c:v libx264 -y -preset ultrafast scrolling.mp4

  


  The original video is 960x540, so the text starts at position y=480 and, after 2 seconds, starts moving up.
That bit works fine, and the text "vanishes" at the top of the frame as it scrolls up.
What I need to achieve is for the text to scroll only within certain Y limits, imagine a virtual box around the text, so it scrolls up only from a certain Y position in the bottom (but not the very bottom) and disappears into a line on the top that isn't the top part of the frame.
Can that be achieved with ffmpeg ?

  


  EDIT : Maybe the trick here should be to put the text on top of a transparent video that's smaller in height, and then within the same command somehow merge this new video that has the text with the original video. Not sure how achieve that though.