Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Welcome to the NHK - 02 [DVDRip 1280x720 x264 FLAC].mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf60.16.100
  Duration: 00:23:41.00, start: 0.000000, bitrate: 936 kb/s
  Stream #0:0[0x1](und): Video: h264 (High 10) (avc1 / 0x31637661), yuv420p10le(tv, bt709, progressive), 1280x720 [SAR 1:1 DAR 16:9], 798 kb/s, 23.98 fps, 23.98 tbr, 24k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc60.31.102 libx264
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 131 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](und): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s (default)
    Metadata:
      handler_name    : SubtitleHandler

encoded with:

for file in *.mkv; do ffmpeg -i "$file" -i "${file%.mkv}.ass" -pix\_fmt yuv420p10le -ac 2 -c:v libx264 -preset slow -c:s mov_text -movflags +faststart -tune animation -me\_range 32 -rc-lookahead 120 -bf 16 -movflags +faststart -flags +global\_header -map\_metadata -1 -map\_chapters -1 -y -crf 21 -y "output/${file%.mkv}.mp4"; done