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• FFmpeg encode an applied filter frame

  10 août 2017, par tqn

  I’m coding an app that crop video to square. I use native lib from ffmpeg like libavfilter, libavformat, ... After apply a filter, my video is cropped to correct size, but when encode and write to output, it seem like it cropped and zoom out everything. Here are the first frame that I extracted to jpeg to debug.

  

  Original Frame

  

  Cropped Frame

  

  Encoded cropped Frame

  I tried both crop function like av_buffersink_get_frame(buffersink_ctx, pFrameSquare) and av_picture_crop((AVPicture *) pFrameSquare, (AVPicture *) pFrame, pic_format, 0, 0) but the output are the same. So what happened ?

• 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 ?

• Fallback input for ffmpeg

  22 septembre 2018, par Daniel Cantarin

  I’m doing some transcoding from a third-party remote input stream that I do not control.

  This input stream has errors from time to time, that I would like to mitigate before sending the stream to my transcoding pipeline, avoiding this way some possible problems in the output.

  I have several ideas regarding different problems. But the most basic scenario I would like to set up is as follows : when the stream is down, or it somehow loses some frames, I want to fill that video gap with a secondary input (like a blank screen, for example).

  For this simple task, I would like to use ffmpeg. I know it can mix, let’s say, an input stream with a fullscreen black square static image. However, I have to deal with this other condition : ffmpeg would run in the same infraestructure for the actual transcoding pipeline. That infraestructure must use its computing power for rendering the output. So, whatever ffmpeg command I end up using should use the minimum possible computing power.

  My actual problem : if I use -vcodec copy, in order to use minimum CPU, I can’t alter the original stream. But if I alter the original stream (by mixing it with some other stream), the operation uses CPU.

  My question : Is there a way to use -vcodec copy, but with a fallback input (instead of a mixed one) for when there are video gaps in the primary stream ?

  Thanks in advance.