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• movenc : Remove an unnecessary condition when flushing fragments

  18 décembre 2014, par Martin Storsjö

  movenc : Remove an unnecessary condition when flushing fragments
  If fragments == 0 it means we haven’t written any moov atom yet.
  
  If the empty_moov flag is set, we already have written an empty moov
  
  atom at startup. Thus, the check for empty_moov is redundant.
  This is in preparation for allowing writing the moov atom later,
  
  even when using the empty moov flag.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavformat/movenc.c

• How can I transform a sequence of images into a playable video using LibVLCSharp ?

  9 février 2021, par adamasan

  I have a sequence of images that I was able to extract from a video using LibVLCSharp. This sample to be more specific. I'm creating a small video library manager for learning purposes, and I would like to extract frames and create thumbnails to play when the user hovers the mouse over the previewer.

  


  Using the aforementioned sample I was able to create a WPF UI around the same loging and extract the frames from a video file. However what I want now is to convert these extracted frames into a video file, using them as preview for the video, just like happens on YouTube.

  


  I wasn't able, however, to find out how to achieve this using LibVLCSharp or just LibVLC. Using this answer on Super User I was able to achieve my goal and put those frames together into a video using ffmpeg.

  


  I haven't taken the time yet to study FFmpeg.Autogen, so I don't know if I would be able to extract the frames from the video files in the same way I can do with LibVLCSharp, but I don't see with good eyes using both libraries on my application, one to export the frames and one to generate these frames into a video.

  


  So, is there a way to get the output frames and convert them into a playable video using LibVLCSharp (or libvlc) itself ?

  


• Can ffmpeg seek when using an input stream (or url) ?

  27 juin 2022, par Roee

  I've been using ffmpeg quite a lot in the past few weeks, and recently I've encountered a very annoying issue - when I use ffmpeg with an input stream (usually, just a url as the input) and try to set a start time (with -ss option), I always get a warn message that says "could not seek to position : XXX".

  



  Then, ffmpeg just starts to download the file, and it ouputs nothing until it has downloaded enough data and got to my desired start time.

  



  I'll give an example :

  



  I use this command to execute ffmpeg :

  



  ffmpeg -ss 50 -re -i https://ascent.usbank.com/acp/videos/041114ascent.flv -b:a 128k -ac 2 -acodec libvorbis -b:v 1024k -vcodec libtheora -strict 2 -preset ultrafast -tune zerolatency -pix_fmt yuv420p -f ogg pipe:1


  



  and I get the warn message

  



  https://ascent.usbank.com/acp/videos/041114ascent.flv: could not seek to position 50.000


  



  Then, it takes about 30 seconds until ffmpeg starts to output data to stdout. And when I try this with longer videos (and longer seek times), it takes even longer.

  



  My question is, what can I do ? I guess it's impossible for ffmpeg to seek when it haven't got the whole input stream... Am I wrong ? Or is there any other solution ?

  



  Of course I try to avoid downloading the entire file from the web...

  



  Thanks in advance !

  



  Roee.