mxf file: play 8 mono tracks as 4 stereo tracks

[SimpelMe]

I do have mxf files with 8 mono tracks inside. We always use them as stereo. So when I want to control my exported files I want to check them in stereo.

Tried a lot. At least I could play the first 2 mono files together as mono:

--lavfi-complex="[aid1][aid2]amix=inputs=2[ao]"

But that's not what we need.

Technical Information

• mpv version

mpv 0.37.0 Copyright © 2000-2023 mpv/MPlayer/mplayer2 projects
 built on Nov 22 2023 01:45:29
libplacebo version: v6.338.2
FFmpeg version: 6.1.1
FFmpeg library versions:
   libavutil       58.2.100 (runtime 58.29.100)
   libavcodec      60.3.100 (runtime 60.31.102)
   libavformat     60.3.100 (runtime 60.16.100)
   libswscale      7.1.100 (runtime 7.5.100)
   libavfilter     9.3.100 (runtime 9.12.100)
   libswresample   4.10.100 (runtime 4.12.100)

• Platform and Version

22.6.0 Darwin Kernel Version 22.6.0: Mon Feb 19 19:45:09 PST 2024; root:xnu-8796.141.3.704.6~1/RELEASE_ARM64_T6000 arm64

• Source of the mpv binary: home brew

Expected behavior

Show 4 audio tracks at on screen display and cycle them with #. All 4 tracks are stereo made from the 8 mono tracks.

Actual behavior

Has 8 mono audio tracks.

[kasper93]

You could use amerge [1] to merge tracks into one and pan [2] to select which channels to map to output.
[1] https://ffmpeg.org/ffmpeg-filters.html#amerge-1
[2] https://ffmpeg.org/ffmpeg-filters.html#pan-1

(not tested, not sure it would work in mpv)

[SimpelMe]

This syntax is at least executed but does not lead to the desired result:

--lavfi-complex="[aid1] [aid2] amerge [a1];[aid3] [aid4] amerge [a2];[aid5] [aid6] amerge [a3];[aid7] [aid8] amerge [a4];[a1] pan=stereo [ao1];[a2] pan=stereo [ao2];[a3] pan=stereo [ao3];[a4] pan=stereo [ao4]; [ao1] [ao2] [ao3] [ao4] amerge=inputs=4"

But it shows some warnings I don't understand:

[ffmpeg] Parsed_amerge_0: No channel layout for input 1
[ffmpeg] Parsed_amerge_1: No channel layout for input 1
[ffmpeg] Parsed_amerge_2: No channel layout for input 1
[ffmpeg] Parsed_amerge_3: No channel layout for input 1
[ffmpeg] Parsed_amerge_8: Input channel layouts overlap: output layout will be determined by the number of distinct input channels
[ffmpeg] Parsed_amerge_0: Input channel layouts overlap: output layout will be determined by the number of distinct input channels
[ffmpeg] Parsed_amerge_1: Input channel layouts overlap: output layout will be determined by the number of distinct input channels
[ffmpeg] Parsed_amerge_2: Input channel layouts overlap: output layout will be determined by the number of distinct input channels
[ffmpeg] Parsed_amerge_3: Input channel layouts overlap: output layout will be determined by the number of distinct input channels

mpv shows audio tracks in gui _/8.

[SimpelMe]

One running ffmpeg line is:

ffmpeg -i input.mxf -filter_complex '[a:0][a:1] amerge [st1]; [a:2][a:3] amerge [st2]; [a:4][a:5] amerge [st3]; [a:6][a:7] amerge [st4]' -map v:0 -map '[st1]' -map '[st2]' -map '[st3]' -map '[st4]' output.mxf

Any chance to get this translated into mpv syntax?

[SimpelMe]

At the end I did it this way.

mpv \
    videofile.mxf \
    --scripts=tracks.lua \
    --lavfi-complex="[aid1] [aid2] amerge [ao]"

tracks.lua is:

options = require 'mp.options'

-- define keys
local opts = {
  -- audio
  a_zero = '0',
  a_one = '1',
  a_two = '2',
  a_three  = '3',
  a_four = '4'
}

options.read_options(opts)

-- info
CLEAR_OSD_TIMEOUT = .01 -- Hack for clearing OSD message upon OSC toggle
osc_always_on = true

function toggle_osc_auto_always()
  osc_always_on = not osc_always_on
  mp.commandv('script-message', 'osc-visibility',
    osc_always_on and 'always' or 'auto'
  )
  mp.add_timeout(CLEAR_OSD_TIMEOUT, function ()
    mp.osd_message('')
  end)
end

-- audio
function select_audio_0()
  mp.set_property("lavfi-complex", "")
  local track = mp.get_property_number("aid")
  if not track then
    track = 0
  end
  track = track + 1
  if track > 8 then
    track = 1
  end
  mp.set_property_number("aid", track)
  mp.set_property("audio-channels", "mono")
  if track == 1 then mp.command('show-text "Track 1"') end
  if track == 2 then mp.command('show-text "Track 2"') end
  if track == 3 then mp.command('show-text "Track 3"') end
  if track == 4 then mp.command('show-text "Track 4"') end
  if track == 5 then mp.command('show-text "Track 5"') end
  if track == 6 then mp.command('show-text "Track 6"') end
  if track == 7 then mp.command('show-text "Track 7"') end
  if track == 8 then mp.command('show-text "Track 8"') end
end

function select_audio_1()
  mp.command('show-text "Tracks 1 + 2"')
  mp.set_property("lavfi-complex", ("[aid1] [aid2] amerge [ao]"):format(1, 2))
  mp.set_property("audio-channels", "stereo")
end

function select_audio_2()
  mp.command('show-text "Tracks 3 + 4"')
  mp.set_property("lavfi-complex", ("[aid3] [aid4] amerge [ao]"):format(1, 2))
  mp.set_property("audio-channels", "stereo")
end

function select_audio_3()
  mp.command('show-text "Tracks 5 + 6"')
  mp.set_property("lavfi-complex", ("[aid5] [aid6] amerge [ao]"):format(1, 2))
  mp.set_property("audio-channels", "stereo")
end

function select_audio_4()
  mp.command('show-text "Tracks 7 + 8"')
  mp.set_property("lavfi-complex", ("[aid7] [aid8] amerge [ao]"):format(1, 2))
  mp.set_property("audio-channels", "stereo")
end

-- info
mp.add_key_binding(nil, 'toggle-osc-auto-always', toggle_osc_auto_always)
-- audio
mp.add_forced_key_binding(opts.a_zero, "Select_Audio_0", select_audio_0)
mp.add_forced_key_binding(opts.a_one, "Select_Audio_1", select_audio_1)
mp.add_forced_key_binding(opts.a_two, "Select_Audio_2", select_audio_2)
mp.add_forced_key_binding(opts.a_three, "Select_Audio_3", select_audio_3)
mp.add_forced_key_binding(opts.a_four, "Select_Audio_4", select_audio_4)

[kasper93]

Converted to discussion. I don't think there is a need for such niche feature in mpv. Patches welcome.