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• Merging 2 videos with overlay causes async problems

  3 novembre 2014, par Gnagy

  I’m using following FFMPEG command to merge 2 MKV inputs with the overlay parameter.
  The result should be one output with input1 on top of input2.
  In the process, the output should be webm.
  Both inputs are of the same length (with a margin of a second).

  ffmpeg -i input1.mkv -i input2.mkv -y -filter_complex [0:v]select=1, setpts=PTS-STARTPTS, scale=400:300, pad=400:600 [top]; [1:v]select=1, setpts=PTS-STARTPTS, scale=400:300 [bottom]; [top][bottom] overlay=0:300 [out]; [0:a:0][1:a:0] amerge=inputs=2 [a]; [a] asetpts=PTS-STARTPTS [a] -map [a] -c:v libvpx -crf 10 -b:v 360K -q:v 7 -c:a libvorbis -b:a 32k -map [out] output.webm

  This command does what it’s supposed to do.

  However, the 2 videos are not totally in sync.

  The input1 on the top plays decently while the input2 on the bottom has black frames, slows down or speeds up and causes the audio and video to be out of sync.

  To rule out the individual quality of the inputs, we switched the position of the videos and the top video always plays decently.

  How can we fix this ?

• Extract specific frames of youtube video without downloading video

  22 janvier 2023, par Kashish Arora

  I need to extract specific frames of an online video to work on an algorithm but I don't want to download the whole video because that would make it highly inefficient.

  


  For starters, I tried working with youtube videos. I can download whole of the video using youtube-dl in this way :

  


  ydl_opts = {'outtmpl': r'OUTPUT_DIRECTORY_HERE',}
with youtube_dl.YoutubeDL(ydl_opts) as ydl:
    ydl.download([url])


  


  And then I can capture individual frames.

  


  I need to avoid downloading the whole video. After some research, I have found that ffmpeg might help me do this. I found no way to download just the frames so if this is not possible, the second option is that I can download specific portions of the video. One such example in linux is here but I couldn't find any solution for python.

  


  What is a good way to download just the frames, or portions of videos (in python) without downloading the entire thing ?

  


• rtmpproto : Validate the embedded flv packet size before copying

  3 octobre 2013, par Martin Storsjö

  rtmpproto : Validate the embedded flv packet size before copying
  This wasn’t an issue prior to 58404738, when the whole RTMP packet
  
  was copied at once and the length of the individual embedded flv
  
  packets only were validated by the flv demuxer.
  Prior to this patch, this could lead to reads and writes out of bound.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavformat/rtmpproto.c