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• 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

  


• avcodec/dca : Unavpriv dca_sample_rates

  9 février 2021, par Andreas Rheinhardt

  avcodec/dca : Unavpriv dca_sample_rates
  Said table is 64 bytes long and exported so that it can be used both
  
  in libavcodec and libavformat. This commit stops doing so and instead
  
  duplicates it for shared builds, because the overhead of exporting the
  
  symbol is bigger than 64 bytes. It consists of the length of the name of
  
  the symbol (2x24 bytes), two entries in .dynsym (2x24 bytes), two
  
  entries for symbol version (2x2 bytes), one hash value in the exporting
  
  library (4 bytes) in addition to one entry in the importing library's
  
  .got and .rela.dyn (8 + 24 bytes).
  
  (The above numbers are for a Linux/GNU/Elf system ; the numbers for other
  
  platforms may be different.)
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/Makefile
  • [DH] libavcodec/dca.c
  • [DH] libavcodec/dca.h
  • [DH] libavcodec/dca_core.c
  • [DH] libavcodec/dca_parser.c
  • [DH] libavcodec/dca_sample_rate_tab.c
  • [DH] libavcodec/dca_sample_rate_tab.h
  • [DH] libavformat/Makefile
  • [DH] libavformat/dca_sample_rate_tab.c
  • [DH] libavformat/spdifenc.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