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• Intercept and divert graphic output before it hits the linux framebuffer, not using X11

  13 octobre 2018, par Apollo

  I have been researching this issue for about a week, and it may be that I don’t know the right questions to ask.

  I am running a debian distro (Raspbian Stretch on the RaspberryPi). I am not using X11. Instead, I am booting straight to the command line, and will eventually probably boot straight up headless, starting a program at startup or sshing in to interact.

  What I need to do is to start an application (a game engine specifically) that draws graphics to the framebuffer. Then, I need to intercept that stream before it makes it into the framebuffer, so I can work with it in real time.

  Ultimately, I am using ffmpeg to compress and stream video of the output to another Pi. So, I want to be able to start an application and stream its output over a LAN, while still being able to interact with the command line in a separate thread.

  I have the ffmpeg command to pull from /dev/fb0, and have successfully started the graphics application and streamed the content. But, is there anyway to intercept, capture, or redirect that application’s output so it never actually hits the framebuffer ? In my searching I have found many examples of writing to or reading from the framebuffer, but nothing about stopping content before it reaches the buffer.

  I am happy with any solution that uses an existing package or application, or for C or RUST code that accomplishes what I need.

  Thank you

• FFMPEG, itsoffset with overlay command not working as it supposed to

  28 septembre 2018, par G.T.

  I managed to overlay two videos one by another with the overlay command and use a nullsrc command to play both video till both of them ended with the following command :

  ./ffmpeg -i first.MOV -i second.MOV -filter_complex "nullsrc=size=1280x400:duration=30[bg];[0]scale=640:-1,pad=1280:400[first];[bg][first]overlay=0:0[base];[1]scale=640:-1[second];[base][second]overlay=640:0" output.mp4

  Now what I wanted to do is to delay one of the overlay till the other one finishes. For this as far as I know the command is itsoffset, so I modified to use this :

  ./ffmpeg -i first.MOV -itsoffset 5 -i second.MOV -filter_complex "nullsrc=size=1280x400:duration=30[bg];[0]scale=640:-1,pad=1280:400[first];[bg][first]overlay=0:0[base];[1]scale=640:-1[second];[base][second]overlay=640:0" output.mp4

  Now my only problem with this is that I want to show the first frame of the delayed video till it starts... And even though somewhere I read that this should do it, it won’t. It leaves it blank till the input starts.

  Any idea how could I add the first frame of second video till the itsoffset starts the video ?

  Update1 : I may found a cheat around it, but the problem with it it’s really slow in the first second or so.

  ./ffmpeg -i first.MOV -i second.MOV -itsoffset 5 -i second.MOV -filter_complex "color=size=1280x400:duration=30[bg];[1]select=eq(n\,0),scale=640:-1[fg];[bg][fg]overlay=640:0[bgc];[0]scale=640:-1[first];[bgc][first]overlay=0:0[firstb];[2]scale=640:-1[second];[firstb][second]overlay=640:0" output.mp4

  Not to mention later on I need to dynamically create the command line string which would be really painful like this.

• Android Media player/framework species

  4 septembre 2018, par sungyong

  I’m confused about species of media player/framework/library of Android and it’s role and positions.

  Here is my understanding about Android media player and framework.
  

  I don’t have confident what I understand, still be under the chaos.

  From Android developer’s guide,
  for application side : apk uses Application Framework which has two players - MediaPlayer, ExoPlayer

  for Native framework side : it has also various players - Nu, awesome, etc.

  There’re some query for gstreamer vs ffmpeg, ffmpeg vs vlc, or exoplayer vs vitamio. It makes me more confusing.

  Would you clearify me to get the right concept for them ?
  If my android custom device use ffmpeg, that means it doesn’t use standard Android media framework ?

  For stagefright engine, there is no alternative for this ?