M1 macs: Preserving HDR, convert all mkv in a folder to 1080P using HandBrakeCLI. Uses VideoToolbox for hardware encoding.

gistfile1.txt

#!/usr/bin/env bash

read -r -d '' profile <<'EOF'
{
  "PresetList" : [
    {
      "AlignAVStart" : true,
      "AudioCopyMask" : [
        "copy:aac",
        "copy:ac3",
        "copy:eac3",
        "copy:dtshd",
        "copy:dts",
        "copy:truehd"
      ],
      "AudioEncoderFallback" : "ca_aac",
      "AudioLanguageList" : [
        "any"
      ],
      "AudioList" : [
        {
          "AudioBitrate" : 960,
          "AudioCompressionLevel" : -1,
          "AudioDitherMethod" : "auto",
          "AudioEncoder" : "copy",
          "AudioMixdown" : "7point1",
          "AudioNormalizeMixLevel" : false,
          "AudioSamplerate" : "auto",
          "AudioTrackDRCSlider" : 0,
          "AudioTrackGainSlider" : 0,
          "AudioTrackQuality" : -1,
          "AudioTrackQualityEnable" : false
        }
      ],
      "AudioSecondaryEncoderMode" : true,
      "AudioTrackSelectionBehavior" : "all",
      "ChapterMarkers" : true,
      "ChildrenArray" : [

      ],
      "Default" : true,
      "FileFormat" : "av_mkv",
      "Folder" : false,
      "FolderOpen" : false,
      "InlineParameterSets" : false,
      "MetadataPassthrough" : true,
      "Mp4HttpOptimize" : false,
      "Mp4iPodCompatible" : false,
      "PictureAllowUpscaling" : false,
      "PictureAutoCrop" : true,
      "PictureBottomCrop" : 0,
      "PictureChromaSmoothCustom" : "",
      "PictureChromaSmoothPreset" : "off",
      "PictureChromaSmoothTune" : "none",
      "PictureColorspaceCustom" : "",
      "PictureColorspacePreset" : "bt2020",
      "PictureCombDetectCustom" : "",
      "PictureCombDetectPreset" : "default",
      "PictureDARWidth" : 1920,
      "PictureDeblockCustom" : "strength=strong:thresh=20:blocksize=8",
      "PictureDeblockPreset" : "off",
      "PictureDeblockTune" : "medium",
      "PictureDeinterlaceCustom" : "",
      "PictureDeinterlaceFilter" : "decomb",
      "PictureDeinterlacePreset" : "default",
      "PictureDenoiseCustom" : "",
      "PictureDenoiseFilter" : "off",
      "PictureDenoisePreset" : "light",
      "PictureDenoiseTune" : "none",
      "PictureDetelecine" : "off",
      "PictureDetelecineCustom" : "",
      "PictureForceHeight" : 0,
      "PictureForceWidth" : 0,
      "PictureHeight" : 1080,
      "PictureItuPAR" : false,
      "PictureKeepRatio" : false,
      "PictureLeftCrop" : 0,
      "PictureLooseCrop" : false,
      "PictureModulus" : 2,
      "PicturePadBottom" : 0,
      "PicturePadColor" : "black",
      "PicturePadLeft" : 0,
      "PicturePadMode" : "none",
      "PicturePadRight" : 0,
      "PicturePadTop" : 0,
      "PicturePAR" : "auto",
      "PicturePARHeight" : 1,
      "PicturePARWidth" : 1,
      "PictureRightCrop" : 0,
      "PictureRotate" : "angle=0:hflip=0",
      "PictureSharpenCustom" : "",
      "PictureSharpenFilter" : "off",
      "PictureSharpenPreset" : "medium",
      "PictureSharpenTune" : "none",
      "PictureTopCrop" : 0,
      "PictureUseMaximumSize" : true,
      "PictureWidth" : 1920,
      "PresetDescription" : "",
      "PresetDisabled" : false,
      "PresetName" : "test hdr",
      "SubtitleAddCC" : true,
      "SubtitleAddForeignAudioSearch" : true,
      "SubtitleAddForeignAudioSubtitle" : false,
      "SubtitleBurnBDSub" : false,
      "SubtitleBurnBehavior" : "none",
      "SubtitleBurnDVDSub" : false,
      "SubtitleLanguageList" : [
        "any"
      ],
      "SubtitleTrackSelectionBehavior" : "all",
      "Type" : 1,
      "UsesPictureFilters" : true,
      "VideoAvgBitrate" : 6000,
      "VideoColorMatrixCodeOverride" : 0,
      "VideoEncoder" : "vt_h265_10bit",
      "VideoFramerate" : "auto",
      "VideoFramerateMode" : "vfr",
      "VideoGrayScale" : false,
      "VideoLevel" : "auto",
      "VideoOptionExtra" : "",
      "VideoPreset" : "quality",
      "VideoProfile" : "auto",
      "VideoQSVDecode" : false,
      "VideoQualitySlider" : 28,
      "VideoQualityType" : 2,
      "VideoScaler" : "swscale",
      "VideoTune" : "",
      "VideoTurboTwoPass" : false,
      "VideoTwoPass" : false,
      "x264Option" : "",
      "x264UseAdvancedOptions" : false
    }
  ],
  "VersionMajor" : 47,
  "VersionMicro" : 0,
  "VersionMinor" : 0
}
EOF

echo "$profile" > /tmp/hdr.json

fd '.*hdr.*mkv' -j 1 -x HandBrakeCLI -Z test\ hdr --preset-import-file /tmp/hdr.json -e vt_h265_10bit -i {} -o {}.1080p.mkv

Preserves most audio and subtitles. Does not delete the original files.