Recherche avancée

Sur d’autres sites (9108)

• Non-RSA TLS1.2 Packet decryption

  7 février 2017, par Joseph Wahba

  I am trying to decrypt a pcap file. This pcap file contains a capture of an HLS encrypted video stream. The pcap contains TLSv1.2 packets.

  Below are some information from the pcap file

  Server Hello message Cipher Suite :

  TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384.

  EC Diffie-Hellman server Params : pubkey (1)

  The Certificate Status message :

  Signature Hash Algorithm Hash : SHA256

  Signature Hash Algorithm Signature : ECDSA

  Client Key Exchange Message

  EC Diffie-Hellman server Params : pubkey (2)

  I tried to follow this Wireshark SSL decryption tutorial. But it seems that it works only for RSA encryptions.
  I have been researching for a while and found this discussion. I am quoting an extract from this discussion :

  There is an important parameter to mind : decryption of a passively
  recorded session (with a copy of the server private key) works only if
  the key exchange was of type RSA or static DH ; with "DHE" and "ECDHE"
  cipher suites, you won’t be able to decrypt such a session, even with
  knowledge of the server private key. In that case, you will need
  either the negotiated "master secret", or to use the server private
  key to actively intercept the connection

  It’s note worthy that I have the client private key. In my case, the client is FFmpeg video streamer (FFplay). I had a look also on the TLS v1.2 RFC.

  My question :

  Is it possible to do a decryption in this scenario ? If yes, what do I need to have to do so ?

  Is the decryption done using the client’s private key or using the pre_shared_master (i.e. Diffie-Hellman) ?

• Use FFMPEG to Save Live CCTV Video Streams that Has Wrong FPS Encoded, Published by Video Clips instead of Frames, and With Nonnegligible Frame Loss

  6 mars 2023, par Crear

  I want to use FFMPEG command line to archive live CCTV video stream (no audio) from Newark Citizen Virtual Patrol (https://cvp.newarkpublicsafety.org) for traffic analysis, previously I was using (I'm just a noob in these commands)
os.system('ffmpeg -t 24:00:00 -i '+address+' -hide_banner -c:v copy -s 640x360 -segment_time 00:15:00 -f segment -strftime 1 -reset_timestamps 1 "'+OutPath+camera_location+'_%Y-%m-%d-%H-%M-%S.mp4"') to archive the videos everyday and segment them into 15-min-long videos.

  


  However, there are several issues.

  


  

  1. The FPS read from the video stream is actually slower than it really is. For example, it's actually 12, but the decoded result says 8, so every time it generates a 15-min-long video, it only pasts 10 11 mins in the real world.

  


  2. Due to unstable frame loss, the FPS is not a stable value either. Therefore, when I manually set the FPS, it usually make the video has wrong length, and sometimes when the stream froze, it keeps waiting because it hasn't finished 15-min-long video. Something I noticed is that it may generate a 15-min-long video, which contains both night and day, started from perhaps 2AM but ended at 8AM.

  


  3. The live CCTV video stream is not frame by frame, but video clip by video clip. Therefore, when I set the -use_wallclock_as_timestamps to 1, the video will be ultra-fast playing the short video clip, then frozen for the rest of time until receiving next video clip.

  


  


  The only thing I can think of is to re-distribute the frames evenly between the timestamp of receiving the current video clip and the timestamp of receiving the prior video clip. What parameters can help FFMPEG to fix the FPS and archive correctly ? I am using FFMPEG to save the video instead of using OpenCV to decode the frame and then encode a video because we have huge amounts of cameras and our legacy Xeon processor had trouble encoding so many frames simultaneously.

  


  Any suggestion is appreciated !

  


• Ffmpeg cpp libav randomly uses high cpu and less gpu or uses high gpu and less cpu with hw accel

  29 avril 2024, par cngkyt

  I am using ffmpeg as library with cpp
the integration of library is perfectly done i am using AVFilterGraph as audio resampler and video pixfmt converter.

  


  I cannot share code because it is a complete library and contains too many files but i can assure there is no problem about code but maybe approach.

  


  My whole class is based on the transcode example of ffmpeg
text

  


  The problem is when i run my program that encodes approx 90 streams

  


  it starts with 25% cpu usage 80% gpu encode usage %85 gpu decode usage with 100% sm utilization

  


  or

  


  it starts with 80% cpu usage 45% gpu encode usage 50% gpu decode usage with 60% sm utilization

  


  when it start like second type of utilization videos are perfect
but when it starts like the first type of utilization videos are freezing

  


  my program uses pure gpu for encoding for all streams but using gpu decoding for every 3 cpu deoding
that means i use hwaccel for 1/3 of streams
because my cards are 4070 ti super and they have 2 NVENC 1 NVDEC chips

  


  my program takes udp streams and encode it and outputs udp mpegts

  


  bitrate and quality settings are persistent across streams depending on resolution

  


  i always test on same streams

  


  the problem happens randomly
but if it starts with high cpu and low gpu utilization it goes on like this
when i restart program problem occurs randomly again

  


  what can couse this

  


  just as an info i have experience on c++ more than 25 years

  


  if there is someone who can teach me something i will be happy

  


  thanks for your further helps

  


  i have tried to reproduce it with compiled ffmpeg instead of my libav library usage
same thing happens but not often

  


  i have tried using hevc_cuvid instead of hwacceleration with avcodec_find_decoder_by_name function