transcode caused by downmix right? How to mitigate?

[ydrol]

Hi all, anyone know why playback of the following mp4 starts ffmpeg transcode when played in a Linux/Chrome browser? (Also happens in the original mkv )

Code:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'some-movie.mp4':
  Metadata:
    major_brand    : isom
    minor_version  : 512
    compatible_brands: isomdby1iso2avc1mp41
    encoder        : Lavf60.16.100
  Duration: 01:59:45.79, start: 0.000000, bitrate: 9553 kb/s
  Chapters:
    Chapter #0:0: start 0.000000, end 288.000000
      Metadata:
        title          : Chapter 01
 ...
   Chapter #0:20: start 6705.125000, end 7185.792000
      Metadata:
        title          : Chapter 21
  Stream #0:0[0x1](eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1920x800 [SAR 1:1 DAR 12:5], 8783 kb/s, 24 fps, 24 tbr, 16k tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id      : [0][0][0][0]
  Stream #0:1[0x2](eng): Audio: eac3 (Dolby Digital Plus + Dolby Atmos) (ec-3 / 0x332D6365), 48000 Hz, 5.1(side), fltp, 768 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id      : [0][0][0][0]
    Side data:
      audio service type: main
  Stream #0:2[0x3](eng): Subtitle: mov_text (tx3g / 0x67337874), 0 kb/s (default)
    Metadata:
      handler_name    : SubtitleHandler
  Stream #0:3[0x4](eng): Data: bin_data (text / 0x74786574)
    Metadata:
      handler_name    : SubtitleHandler
Unsupported codec with id 98314 for input stream 3

From the logs I'm guessing it's audio downmix? If I added a 2.0 track would that stop on-demand transcode?

Code:

[color=#000000]MediaBrowser.MediaEncoding.Transcoding.TranscodeManager: "/usr/lib/jellyfin-ffmpeg/ffmpeg" "-analyzeduration 200M -probesize 1G -fflags +genpts  -i file:\"/media/movies.tmp/some-movie.mp4\" [/color]
map_metadata -1 -map_chapters -1 -threads 0 -map 0:0 -map 0:1 -map -0:s -codec:v:0 copy -bsf:v h264_mp4toannexb -start_at_zero -codec:a:0 libfdk_aac -ac 2 -ab 256000 -af \"volume=2\" -copyts -avoid_negative_ts disabled
 -max_muxing_queue_size 2048 -f hls -max_delay 5000000 -hls_time 6 -hls_segment_type fmp4

[TheDreadPirate]

AFAICT, Edge and Safari are the only two browsers that support Dolby audio.

https://professionalsupport.dolby.com/s/...uage=en_US