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• Compress video like whatsapp

  10 juillet 2021, par user1079425

  I'm not an expert in Video Editing but what I want to understand the logic of Whatsapp video processing.

  



  First of all I have noticed that whatever the file is, Whatsapp sets the limit of Uploaded videos to 16MB, after which whatsapp crops the video to not exceed the limit. is this a convention or it's a personal choice ?

  



  Secondly, When a video is recorded using the Camera it's not compressed by default, so whatsapp compresses it using FFMPEG I guess, and it takes no time. (tried for a video of 1min 1920x1080 with 125MB of size, becomes 640x360 with 5MB of size in no time, and the upload starts automatically).. how may they do this ? and why the choice of 640x360, It seems to me very fast for 2 asynchronous tasks : Compression + Upload.

  



  When I run the compression command ffmpeg -y -i in.mp4 -codec:v libx264 -crf 23 -preset medium -codec:a libfdk_aac -vbr 4 -vf scale=-1:640,format=yuv420p out.mp4 it takes approximatively 1 min and the video is being rotated !! :D

  



  Finally, when we download a video from Youtube it's already compressed (I guess) and whatsapp doesn't even try to compress it. So I think that it automatically detects thats the video is compressed. How can we detect this ?

  



  Thank you.

  


• Use FFmpeg for continuous streaming from other source

  28 septembre 2017, par widgg

  We have an app that pipes its output, and its output is compress H264 data. The source of the data is from a 3d engine running in same app.

  We can easily pipe the output in FFmpeg to save as mp4 or even m3u8.

  It’s also possible to turn FFmpeg as a server to feed video files.

  So our objective is to have FFmpeg read that data, convert into into mp4 or m3u8 internally and then stream so that it can be read in the web browser.

  We don’t care about be able to replay some file, go back in time or whatever, we just care about the current value.

  Is there a way to do that ? Or a similar solution that would allow some close to that.

  Thanks

  I guess, if it’s possible, it’s like wanting to stream your personal webcam into the web browser. Then you could connect to that and see what is happening at home or wherever your webcam is.

• How can I programmatically write and read random video watermarks ?

  13 novembre 2017, par GreenTriangle

  I spent a few minutes trying to think of a clearer way to word my title, but I couldn’t manage it, sorry.

  I want to essentially canary trap video files : I am (hypothetically, this is not real but a personal exercise) offering them up to 5,000 different people, and if one gets leaked, I want to know who leaked it. Metadata is too easily emoved, so what I’d like to do is add a random and subtle watermark to each file, and store information about that in a database.

  For example : on Joe Smith’s copy, a 10x10 pixel 80% transparent red square in the upper left corner for 5 frames. On Diane Brown’s copy, a full-width 5-pixel 90% transparent black bar on the bottom edge for 15 frames. Then, if I find a leaked copy, I could check it against the database.

  I know this still isn’t foolproof : cropping would break co-ordinates, hue/brightness transforms would break colour reading, cutting time would break timestamps. But if I did want to do this anyway, what would be a good strategy for it ?

  My idea was to generate PNG overlays randomly, split the video into parts with mkvtoolnix/ffmpeg, re-encode the middle part with ffmpeg + overlay filter, and then rejoin them. But is this silly when there’s a "proper" way to do it ? And what would I be doing to read the watermarks, which I can’t even really conceive of ?