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• Streaming to Twitch with FFMpeg

  18 décembre 2014, par Josh Raymond

  I’m using the following script to try and stream my linux desktop to Twitch.tv, I have the stream working, mostly. Unfortunatly, I’m unable to get it to stream my SECOND monitor instead of just my first..

  Here’s the script

  #! /bin/bash
  
  INRES="1900x600"
  
  OUTRES="800x600"
  
  INAUD="pulse"
  
  FPS="25
  
  STREAM_KEY=$(cat ~/.twitch_key)
  
  STREAM_URL="rtmp://live.twitch.tv/app/$STREAM_KEY"
  
  
  
  ffmpeg \
  
  -f alsa -ac 2 -i "$INAUD" \
  
  -f x11grab -s "$INRES" -r "$FPS" -i :0.0+1280,0 \
  
  -vcodec libx264 -s "$OUTRES" -pix_fmt yuv420p \
  
  -acodec libmp3lame -threads 6 -qscale 5 -b 64KB \
  
  -f flv -ar 44100 "$STREAM_URL"

  Everything works as it should (after a few hiccups I solved on my own before coming here)
  But I was wondering if there was a way to pipe TWO audio inputs into ffmpeg ? One for the system sounds (IE game) and one for my mic ? I use Pulseaudio and have pavucontrol, if that matters.

  Thanks in advance.

• FFMPEG extract frame-accurate video fragments with minimal transcoding

  9 mars 2018, par Leeroy

  How can I extract frame-accurate video or audio fragments using FFMPEG without transcoding the full portion ?

  ffmpeg -i input.mp4 -ss 00:00:01.234 -to 00:00:05.678 output.mp4 works because it re-encodes... If I use -codec: copy then it disregards the precision of my start and end time arguments and instead uses the closest keyframe (I understand).

  Is there a command or combination of commands to instruct FFMPEG to transcode only what’s needed, the bits near the start/end markers, up to keyframes ?

  EDIT : A bit of context... I’m trying to write this function to process video piped from youtube-dl, perhaps even as a service. So it matters that I minimize bandwidth (downloading to timestamp and discarding after) and CPU utilization (re-encoding all of the fragment).

• Input seeking for frame at specified timestamp with Py-AV

  9 décembre 2019, par neonScarecrow

  I have a project already using Py-AV and am trying to replicate a specific ffmpeg command. The goal is to get a frame roughly around the specified timestamp.

  Here’s the ffmpeg commmand :
  https://trac.ffmpeg.org/wiki/Seeking

  ffmpeg -ss 14 -i https://some_url.mp4 -frames:v 1 frame_at_14_seconds.jpg

  Here’s my code :

      #return one frame around 14 seconds into the movie
  
      target_sec = 14 
  
      container = av.open('https://some_url.mp4', 'r')
  
      container.streams.video[0].thread_type = 'AUTO'
  
      video_stream = next(s for s in container.streams if s.type == 'video')
  
      time_base = float(video_stream.time_base)
  
      target_timestamp = int(target_sec / time_base) + video_stream.start_time
  
      video_stream.seek(target_timestamp)
  
      for frame in container.decode(video_stream):
  
          frame.to_image().save('frame_at_14_seconds.jpg')
  
          break

  Additionally, I have found any documentation about this, but does anyone know if either command (ffmpeg/av.open) is downloading the entire file to a tmp file behind the scenes. I’m looking for a less memory-intensive way to read a frame for every second in an up to 60 second video.