Amlogic-NO discussion

Development Development & Testing
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As @Joe_90 mentioned issues with 5.0 audio files, I decided to make some thorough tests.

TL;DR: 4ch and 5ch (5.0) non-passthrough audio is currently broken in CE-NO since 20250417 using kernel 5.15.153

As this forum helped me a lot when I needed, I’m going to post the test methodology so anyone can perform the same tests on their own equipment.

IMPORTANT: These tests only make sense if you own an AVR connected to real loudspeakers! Soundbars and all “channel virtualization” systems are out by definition as you can not distinguish channels audio output with certainty.

IMPORTANT: On your own PC, not on CE of course!

  • We need a sensible 5.1 audio file with clearly identifiable channels to avoid any mistake. We’ll download this 5.1 Dolby Surround Test from YouTube in the right format
    yt-dlp -f 380 -o DD51Test.m4a 'https://www.youtube.com/watch?v=PqVCPE8_ntE'

  • Extract only the useful audio part of this demo between 9s and 45s for our purpose. This will become our master file to create all further test files
    ffmpeg -hide_banner -ss 9 -to 45 -i "DD51Test.m4a" -vn -codec:a copy "DD51Test.ac3"

  • We’re going to create some test files with different channels. From the master AC3 file, we’ll create FLAC files to make sure no passthrough is involved. Namely, we’ll have:

    1. AudioLayout-5.1.flac → 6ch → FL+FR+FC+LFE+SL+SR (a literal copy of the AC3 master)
      ffmpeg -hide_banner -i DD51Test.ac3 -channel_layout '5.1(side)' -codec:a flac "AudioLayout-5.1.flac

    2. AudioLayout-5.0.flac → 5ch → FL+FR+FC+SL+SR
      We limit the duration to 30.5s as it does not make sense to include the LFE part which does not exist with this layout.
      ffmpeg -hide_banner -to 30.5 -i DD51Test.ac3 -codec:a flac -filter:a "pan=5.0(side)| c0=FL | c1=FR | c2=FC | c3=SL | c4=SR" AudioLayout-5.0.flac

    3. AudioLayout-quad.flac → 4ch → FL+FR+SL+SR
      We limit the duration to 30.5s as it does not make sense to include the LFE part which does not exist with this layout. Also, because there’s no FC (Front Center) channel, there will be a small gap between FL and FR sound.
      ffmpeg -hide_banner -to 30.5 -i DD51Test.ac3 -codec:a flac -filter:a "pan=quad(side)| c0=FL | c1=FR | c2=SL | c3=SR" AudioLayout-quad.flac

    NOTE: All these multichannel files use the “side” variant of the layout because this by far the most common layout found in the wild. The term “side” refers to the side channels in opposition to back channels (ie: SideLeft instead of BackLeft and so on). In 5.0/5.1 layouts, there’s is no notion of “back” channels, hence the “side” variant. Anyway, this not an issue because all the AVRs adapt the channel layout to the available physical loudspeakers so it always works as it should.

    NOTE 2: 4ch is a bit special on the layout side! 4.0 and 4.1 are extremely rare (never seen one myself) and unsupported by FLAC (and many others) as they use FR+FL+FC+BC or FR+FL+FC+LFE+BC (ie: FrontCenter and BackCenter). Only “quad” and “quad(side)” exist in the wild and as for 5.0/5.1 the “side” part is routed as it should by all AVRs to the corresponding loudspeakers.

  • So now, we’ll test to make sure we have the right channels at the right place and did not create bogus files which could lead to bad test results.

    1. Using FFPlay
      ffplay -hide_banner -f lavfi 'amovie=DD51Test.ac3,asplit[out1][a];[a]showvolume=w=500:h=50[out0]'
    2. Using MPV for those who prefer this amazing player
      mpv --lavfi-complex="[aid1]asplit[ao][audio1];[audio1]showvolume=w=500:h=50[vo]" DD51Test.ac3
      Replace DD51Test.ac3 with any of the FLAC files to see the result and familiarize yourself with what is the expected output.

  • Nearly done… Just copy the FLAC files somewhere accessible by Kodi and within a path declared as a Music source. Play them and see how your system react.

In my case, Dune HD Homatics Boxr 4K connected to a modern Denon AVR I have the following results:

  • AudioLayout-5.1.flac → :white_check_mark: Plays perfectly with output as expected
  • AudioLayout-5.0.flac → :x: FL and FR play ok, no FC, no SL, no SR and finally the SR (Right surround) plays on the center channel (FC)
  • AudioLayout-quad.flac → :x: FL and FR play ok, no SL, no SR, no more sound after FL and FR.

These results are consistent from CE-NO 20250417 to 20250625 which I currently use, all featuring kernel 5.15.153.