ffmpeg - Encoding - GPU Encoding

NOTE:

• -i “input.mkv” is the source file.
• -vaapi_device /dev/dri/renderD128 is a shortcut to -init_hw_device vaapi=vaapi0:/dev/dri/renderD128 -filter_hw_device vaapi0, and initializes a new hardware device of type vaapi.
• -vf 'format=nv12,hwupload,scale_vaapi=w=1920:h=1080' creates the filtergraph and uses it to filter the stream.
  • The encoders only accept input as VAAPI surfaces. If the input is in normal memory, it will need to be uploaded before giving the frames to the encoder - in the ffmpeg utility, the hwupload filter can be used for this.
  • It will upload to a surface with the same layout as the software frame, so it may be necessary to add a format filter immediately before to get the input into the right format (hardware generally wants the nv12 layout).
  • The hwupload filter also requires a device to upload to, which needs to be defined before the filter graph is created which is done with -vaapi_device.
  • The scale_vaapi=w=1920:h=1080 scales the video to 1080p.
  • Use -vf 'format=nv12,hwupload' to not do any scaling, and to use NV12 (8-bit encoding).
  • Use -vf 'format=p010,hwupload' for 10-bit encoding; and also change the profile to Main10.
    • See further below for other pixel formats..
• -map 0:v selects the Video streams from the inputs which will go into the output.
• -metadata:s:v:0 language=eng has the output Video stream to show English as the language.
• -map 0:a selects the Audio streams from the inputs which will go into the output.
• -map 0:s? selects the Sub-Title streams from the inputs which will go into the output.
  • The “?” is to have this optional, i.e. only write Sub-Titles if they exist in the source.
• -c:v hevc_vaapi converts the input file to H.265 in the destination file.
  • hevc_vaapi means H.265 / MPEG-H part 2 (HEVC).

  • Instead of using the H.265 codec, optionally select any other code that the GPU supports.

    To figure out for which codecs the GPU supports, run the following command:

    vainfo

    This returns something like this:

          VAProfileH264ConstrainedBaseline:	VAEntrypointVLD
          VAProfileH264ConstrainedBaseline:	VAEntrypointEncSlice
          VAProfileH264Main               :	VAEntrypointVLD
          VAProfileH264Main               :	VAEntrypointEncSlice
          VAProfileH264High               :	VAEntrypointVLD
          VAProfileH264High               :	VAEntrypointEncSlice
          VAProfileHEVCMain               :	VAEntrypointVLD
          VAProfileHEVCMain               :	VAEntrypointEncSlice
          VAProfileHEVCMain10             :	VAEntrypointVLD
          VAProfileHEVCMain10             :	VAEntrypointEncSlice
          VAProfileJPEGBaseline           :	VAEntrypointVLD
          VAProfileVP9Profile0            :	VAEntrypointVLD
          VAProfileVP9Profile2            :	VAEntrypointVLD
          VAProfileAV1Profile0            :	VAEntrypointVLD
          VAProfileAV1Profile0            :	VAEntrypointEncSlice
          VAProfileNone                   :	VAEntrypointVideoProc

    For all entries with a value of VAEntrypointEncSlice hardware encoding is supported and can be used.

• -c:a copy copies the Audio streams without modification to the output.
• -c:s copy copies the Subtitle streams without modification to the output.
• -rc_mode CQP sets the rate control mode to CQP.
  • CQP works well.

  • Run the following to see all possible modes:

    ffmpeg -h encoder=hevc_vaapi

    This returns all H.265 VAAPI options. These are the available rate control modes:

    ...
      -rc_mode           <int>        E..V....... Set rate control mode (from 0 to 6) (default auto)
         auto            0            E..V....... Choose mode automatically based on other parameters
         CQP             1            E..V....... Constant-quality
         CBR             2            E..V....... Constant-bitrate
         VBR             3            E..V....... Variable-bitrate
         ICQ             4            E..V....... Intelligent constant-quality
         QVBR            5            E..V....... Quality-defined variable-bitrate
         AVBR            6            E..V....... Average variable-bitrate
    ...

• -global_quality 25 selects the video quality.
  • The default value is 25 which returns decent enough output.
  • The lower the value, the better is the video quality, but the output file gets larger.
• -profile:v main selects the x265 profile, main, which should work with every output device.
  • For h.265, main is the default profile. All decoders, which can decode h.265, will support it.
  • But there are other profiles that can be used, for supporting additional decoder capabilities like higher colour depth (10, 12 or 16 bit), less subsampling (4:2:2 or 4:4:4) or intra-constrained (mainly for editing, as it's not efficient). Plus more specialized things.
  • Main 10 is fine to use for 8 or 10 bit color depths and its inclusion in version 1 of the standard means it will enjoy a high level of support as long as the decoder supports 10 bit.
• -v verbose
• output.mkv is the output file.

NOTE: When using a different pixel format, usually the following options will need to be set:

• -vf 'format=nv12' and -profile:v main
• -vf 'format=p010' and -profile:v main10
• -vf 'format=p016' and -profile:v rext