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• Append two videos without duplicating FFMPEG

  10 septembre 2021, par Hasindu Lanka

  Let's say we have 2 video files (X,Y) in the same format, codec and dimensions.

  


  X is a longer video with several gigabytes in size. Y is a short 10 second video. I want to append Y to the end of X without creating another copy of X (Because it's big in size)

  


  I have to repeat this process for hours with many 10 second videos arriving one after another.

  


  Currently, I'm concatenating files using ffmpeg.

  


  ffmpeg -f concat -safe 0 -i chunk.list -c copy final-video.mkv

  


  chunk.list contains file names of X and several 10 second videos. After this, X will be deleted and replaced by final-video.mkv. Then, repeat.

  


  But this needs twice the storage capacity and I/O operations. How to do this without creating duplicates ?

  


  It's okay to duplicate these 10 second videos. But duplicating that bigger file X really hurts performance.

  


  Additional info :

  


  All these videos will be encoded with H264, H265, VP8 or VP9 and contained in MKV or MP4 as they are codec copy friendly. Only one of these formats will be used.

  


  This is for a special case screen recorder that's supposed to run on cloud and preemptive remote desktops (Linux).
HTML/JS browser front-end captures the screen and sends to the back-end (Golang) as chunks through HTTP. Network route is undefined and unreliable as there can be firewalls/proxies between the front-end and the back-end. Therefore, we can't use connections like UDP. So the only option is to send video chunks using HTTP.

  


  It's FOSS on https://github.com/HasinduLanka/screencorder

  


• avformat/mpegts : fix max_packet_size in mpegts payload parsing

  21 septembre 2021, par Marton Balint

  avformat/mpegts : fix max_packet_size in mpegts payload parsing
  The maximum allowed useful PES payload data was set to PES_packet_length, but
  
  it is in fact smaller by the length of the PES header.
  This changes how corrupt streams are packetized :
  
   If PES header length is bigger than PES_packet_length then the PES packet
  
    payload will be handled as an unbound packet
  
   PES packets with payload across multiple MPEGTS packets will always be
  
    splitted if with the next chunk of data the payload should exceed
  
    PES_packet_length, previously a PES_header_length amount of excess was
  
    allowed.
  Fixes ticket #9355.
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavformat/mpegts.c

• x264/x265 options for fast decoding while preserving quality

  18 août 2024, par user3301993

  I want to encode some videos in H264 and H265, and I would like to ask for help in order to chose the adequate options in x264/x265.

  


  

  • My first priority is video quality. Lossless would be the best quality for example

  


  • My second priority is fast decoding speed (ie : I would like faster decoding without sacrificing quality)

    

    • fast decoding for me means that the decoding machine would use less CPU resources reading the resulting video

    


    • Less RAM consumption would be a plus

    


    • Latency is not important

    


    


  


  • I don't care that much if the output file ends up bigger. Also, encoding speed is not important

  


  


  I'm aware of the option -tune fastdecode in both x264 and x265. But apparently the quality gets a bit worse using it.

  


  For x264 :

  


  -tune fastdecode is equivalent to --no-cabac --no-deblock --no-weightb --weightp 0 (My source is x264 --fullhelp)

  


  Which options preserve quality ?

  


  For x265 :

  


  -tune fastdecode is equivalent to --no-deblock --no-sao --no-weightp --no-weightb --no-b-intra (according to x265 doc)

  


  Again, which options preserve quality ?

  


  I tried to read some documentation on these options, but I'm afraid I'm too stupid to understand if they preserve quality or not.

  


  To explain further what I mean by "preserving quality" :

  


  


  I don't understand what the cabac option does exactly. But let's say for example that it adds some extra lossless compression, resulting in a smaller video file, but the decoding machine would need to do extra work to decompress the file

  


  In that case, the --no-cabac option would skip that extra compression, resulting in no loss of quality, with a bigger file size, and the decoding machine would not need to decompress the extra compression, saving CPU work on the decoding side

  


  In this scenario, I would like to add the --no-cabac option, as it speeds up decoding, while preserving quality.

  


  


  I hope I could get my point across

  


  Can anyone help me pick the right options ?

  


  Thanks in advance