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c/programmer_humor · by ulterno@programming.dev · 329d

Unexpected Asymptote - FLAC

ffmpeg ... -c:a flac -exact_rice_parameters 1 -multi_dim_quant 1 ...

I was encoding wav to flac.

  • With default options, the result was almost instant
    • At > 500x speed
  • Used -compression_level 12, finished in ~ 7 seconds
    • speed = 48.9x
  • Then I used multi_dim_quant
    • After ~ 10 minutes, I checked the speed to be ~ 0.02x. So thought it would take an hour or so. 1.30 seconds worth of audio was encoded
    • It's been over 2 hours now.
      • Shows 1.46 seconds of audio encoded with current speed = 0.00017x

Considering running it in a VM, so I can "pause" it whenever I need to restart my computer.

Update:
size= 123KiB time=00:00:02.82 bitrate= 356.3kbits/s speed=4.68e-05x
It stopped trying to use layman notation.
I'll need to restart soon-ish, but I'll see how far this goes and if the 2.82 seconds of audio is even listenable.

24 points · 13 comments · view on lemmy.world

13 Comments

xxce2AAb@feddit.dk · 12 pts · 329d (4 replies)

Or, and hear me out, you could maybe reevaluate whether you really need the very marginal compression improvements offered by multi dimensional quantization.

ulterno@programming.dev · 13 pts · 329d (3 replies)

This try was actually me evaluating the thing.

Now I am considering reevaluating whether evaluating the option is viable for me.

xxce2AAb@feddit.dk · 11 pts · 329d (2 replies)

Now I am considering reevaluating whether evaluating the option is viable for me.

...Have you ever considered a career in the Civil Service?

ulterno@programming.dev · 4 pts · 329d (1 reply)

If they give WFH, I'll sign up.

xxce2AAb@feddit.dk · 3 pts · 329d

Yeah, that's fair.

brucethemoose@lemmy.world · 7 pts · 329d (2 replies)

Heh, joke's on you; you're using the wrong library for obsessive FLAC compression anyway:

http://cue.tools/wiki/FLACCL

0.00017x sounds like a bug though. Maybe it balloons RAM usage enough to trigger swapping?

ulterno@programming.dev · 3 pts · 329d (1 reply)

Maybe it balloons RAM usage enough to trigger swapping?

Well, my RAM usage doesn't seem to have increased though (at least from this process).
And I haven't setup a swap.

http://cue.tools/wiki/FLACCL

Oh, it has a CUDA library!?
Then this FFmpeg FLAC library is really basic, considering it has no parallelism. I was assuming that the algorithm itself is not parallelisable.

brucethemoose@lemmy.world · 6 pts · 329d

It's OpenCL, so it should even run on integrated graphics.

Yeah, it's great! Extremely fast and marginally smaller than ffmpeg, last I checked, though I have not messed with those newer ffmpeg options. And cuetools has some other nice utilities anyway.

ulterno@programming.dev · 2 pts · 329d (2 replies)

I realise I wasn't able to make this look funny.

BTW, the resultant bitrate from the same source file with:

  • default options : 706.8 kb/s
  • -compression_level 12 : 698.1 kb/s
  • with -exact_rice_parameters 1 -multi_dim_quant 1 that I am trying right now, it currently shows the bitrate to be 331.4 kb/s
    • but it's only encoded the first 1.88 seconds yet, so no idea if it really will manage such an impressive compression.
solrize@lemmy.ml · 2 pts · 329d (1 reply)

I don't see where the humor is, but I have an idle server so might let it run for a few days to compress a half minute of audio at .00017x. But are you sure it isn't just stuck?

ulterno@programming.dev · 0 pts · 328d

Well, the time value is definitely going forward, so I won't expect that, but then a similar thing happens quite a bit with video stuff, so maybe you're right.
Similar, not same, because in that case, it starts showing speed=N/A

ExperimentalGuy@programming.dev · 2 pts · 329d (1 reply)

Make sure you report this to ffmpeg directly at this link: https://ffmpeg.org/bugreports.html

ulterno@programming.dev · 2 pts · 328d

I am currently thinking that it might just be the problem with me having set too high parameters, but considering that mpv is unable to recognise the format even after 2 seconds of audio, perhaps there is some bug.