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• What open source software would be best for reading in raw data from an SDR / USRP and decoding ATSC1.0 video and playing it?

  18 August 2023, by railsnoob

  I've had luck with GNU Radio for ATSC1.0 decode from USRP data and sending the mpeg transport stream to VLC to be played but eventually I would like to have other DTV standards decoded.

  


  I started looking into packages with full DTV support and saw that VLC has TV tuner control/access, but if I have a USRP I'm not sure I could configure VLC to control that, or if I'd even want it to. But since it can go from tuner control to video playback there must be a command/configuration which just has it read from a raw data file that I captured from the USRP, right?

  


  Does anyone know how to go from raw captured ATSC channel to MPEG transport stream on VLC, FFMPEG, or any other software packages?

  


• How can I open a video encrypted with FFMPEG using openCV?

  19 July 2023, by Richard S.J. Hwang

  I am developing a program that encrypts and saves video files and allows them to play only in programs that have key values. (by C#)

  


  I was looking for a way to encrypt a video file and found a way to encrypt it using FFMPEG's CENC.

  


  ffmpeg -i SampleVideo.mp4 -vcodec copy -acodec copy -encryption_scheme cenc-aes-ctr -encryption_key 76a6c65c5ea762046bd749a2e632ccbb -encryption_kid a7e61c373e219033c21091fa607bf3b8 SampleVideo_encrypted.mp4

  


  ffplay SampleVideo_encrypted.mp4 -decryption_key 76a6c65c5ea762046bd749a2e632ccbb

  


  ffmpeg -decryption_key 76a6c65c5ea762046bd749a2e632ccbb -i SampleVideo_encrypted.mp4 -vcodec copy -acodec copy SampleVideo_decrypted.mp4

  


  FFmpeg: how to produce MP4 CENC (Common Encryption) videos

  


  It is easy to encrypt and makes use of the header information of the video file.

  


  But I couldn't find a way to apply decryption at the same time as the Capture Video of OpenCV.
I thought I could use FFMPEG of OpenCV Backend and set the options, so I found a way to set the Windows environment variable, but it didn't work.(Only the gray screen is output.)
As a result of the search, only options related to H/W acceleration appear in OS environ.

  


  How to add ffmpeg options to VideoCapture
(Post written in python)

  


  import os
os.environ["OPENCV_FFMPEG_CAPTURE_OPTIONS"] = "video_codec;h264_cuvid"
cap = cv2.VideoCapture(url)


  


  Code I tested (not worked, c#)

  


  System.Environment.SetEnvironmentVariable("OPENCV_FFMPEG_CAPTURE_OPTIONS",
                                          "decryption_key;76a6c65c5ea762046bd749a2e632ccbb");
VideoCapture video = new VideoCapture(filename, VideoCaptureAPIs.FFMPEG);
...


  


  How can I open a video encrypted with FFMPEG using openCV?

  


  Regards.

  


• is there a way to change dynamic the water mark text color when using ffmpeg depending on the background color when recording a vieo file?

  11 July 2023, by Shelly Ron

  This command in the command prompt window is working fine and recording the entire screen:

  


  ffmpeg -f gdigrab -framerate 24 -i desktop -preset ultrafast -pix_fmt yuv420p out.mp4


  


  this command prompt add a water mark text in the middle of the screen in white color:

  


  ffmpeg -f gdigrab -framerate 24 -i desktop -vf "drawtext=fontfile=path/to/arial.ttf:text='All rights reserved to ...':fontsize=24:fontcolor=white:x=(w-text_w)/2:y=(h-text_h)/2" -preset ultrafast -pix_fmt yuv420p out.mp4


  


  the problem is that the water mark text is in white and i can see it only when the background window color is black for example when i bring to the front the ffmpeg console window:

  


  

  


  but when it's recording some window with white background, because the text is white it can't be seen.

  


  I want to update the command prompt of the ffmpeg to make somehow dynamic so if the background window is black show the water mark text in white and then if I'm bringing up a window with background white change the water mark text automatic to black.

  


  this is the command i tried for the dynamic effect but it didn't work i got errors and then i tried so many versions of the command line, but nothing helped or worked.

  


  ffmpeg -f gdigrab -framerate 24 -i desktop -filter_complex "[0:v]drawtext=text='Watermark Text':x=(w-text_w)/2:y=(h-text_h)/2:fontfile=arial.ttf:fontsize=24,format=rgba [txt];[txt]split=2 [bw][wc];[bw]lut=r=val*2 [b];[wc]lut=r=val*0.5+0.5:g=val*0.5+0.5:b=val*0.5+0.5 [wc];[wc][b]alphamerge [wm];[wm][0:v]overlay=10:10[outv]" -c:v libx264 -preset ultrafast -map "[outv]" out.mp4


  


  and also tried this

  


  ffmpeg -f gdigrab -framerate 24 -i desktop -filter_complex "[0:v]drawtext=text='Watermark Text':x=(w-text_w)/2:y=(h-text_h)/2:fontfile=Arial.ttf:fontsize=24,format=rgba [txt];[txt]split=2 [bw][wm];[bw][1:v]split=3 [b][g][r];[b]geq=r=0:g=0.5:b=0 [b];[g]geq=r=0:g=0:b=0.5 [g];[r]geq=r=0.5:g=0:b=0 [r];[wm][b][g][r]merge=3,format=rgba [watermark];[0:v][watermark]overlay=x=(W-w)/2:y=(H-h)/2" -map "[watermark]" -map 0:a? -c:v libx264 -c:a copy -preset ultrafast out.mp4