1229286 - AAC and Vorbis audio playback fails with small ALSA buffer sizes

Status: RESOLVED INVALID

(Core :: Audio/Video: cubeb, defect)

Description

[Radosław Szkodziński]

It seems that Vorbis and AAC, but not Opus audio playback fails (looks stopped) on ALSA output when buffer size is too small. Pulseaudio is not affected, probably because it allocates the buffer you ask for.

Here's my ALSA config that fails. Changing buffer_size to 2048 in the frontend loopback devices makes the playback work.

Tested on Firefox 42, 43b7 and 45a1 nightly.

# /etc/asound.conf

defaults.pcm.rate_converter "speexrate_best"

# playback PCM device: using loopback subdevice 0,0
pcm.amix {
  type dmix
  ipc_key 219345
  slave {
  	pcm "hw:Loopback,0,0"
	period_size 256
	buffer_size 1024
	rate 48000
	format S32_LE
	channels 2
  }
}

# capture PCM device: using loopback subdevice 0,1
pcm.asnoop {
  type dsnoop
  ipc_key 219346
  slave {
  	pcm "hw:Loopback,0,1"
	period_size 256
	buffer_size 1024
	rate 48000
	format S32_LE
	channels 2
  }
}

# duplex device combining our PCM devices defined above
pcm.aduplex {
  type asym
  playback.pcm "amix"
  capture.pcm "asnoop"
}

# ------------------------------------------------------
# for zita-a2j and zita-j2a: looped-back signal at other ends
pcm.ploop {
  type dsnoop
  ipc_key 219348
  slave {
  	pcm "hw:Loopback,1,0"
	period_size 256
	buffer_size 1024
	rate 48000
	format S32_LE
	channels 2
  }
}

pcm.cloop {
  type dmix
  ipc_key 219347
  slave {
  	pcm "hw:Loopback,1,1"
	period_size 256
	buffer_size 1024
	rate 48000
	format S32_LE
	channels 2
  }
}

# ------------------------------------------------------
# default device

pcm.!default {
  type plug
  slave.pcm "aduplex"
}

Comment 1

[Matthew Gregan [:kinetik]]

(In reply to Radosław Szkodziński from comment #0)
> It seems that Vorbis and AAC, but not Opus audio playback fails (looks
> stopped) on ALSA output when buffer size is too small. Pulseaudio is not
> affected, probably because it allocates the buffer you ask for.

Can you please post a link to the working and failing media?  The sample format probably plays a role in the bug.

Comment 2

[Radosław Szkodziński]

This was tested with Youtube videos and Wikimedia commons.

https://www.youtube.com/watch?v=ZDrb82L_D7M - fails, WebM VP9 w/ AAC. If ffmpeg is disabled via about:config, picks WebM VP9 w/ Vorbis, also fails.
https://www.youtube.com/watch?v=sit6zUQKpJc - works, WebM VP9 w/ Opus.

https://upload.wikimedia.org/wikipedia/commons/f/f0/Amazing_Grace_%28USAFB_jazz_vocal%29.ogg - fails, Ogg Vorbis.
http://download.blender.org/peach/trailer/trailer_1080p.ogg - works, Ogg Theora w/ Vorbis. (Different encoder?)

Comment 3

[Radosław Szkodziński]

By "fails" above I mean that video plays, but audio does not.

In case of the <audio> file, the playback and seeking seem frozen as if buffering.
I've also tested it with downloaded audio streams from the above Youtube videos.

Comment 4

[Matthew Gregan [:kinetik]]

Looks like the bug lies within the ALSA stack:

11:25 < AstralStorm> so now I'm pretty sure it's a bug in lfloat plugin somewhere
11:36 < AstralStorm> you shouldn't use period_size + buffer_size
11:37 < AstralStorm> it's either period_size + buffer_*time* or periods + buffer_size
11:50 < AstralStorm> ALSA is broken wrt period_size/buffer_size somehow
11:50 < AstralStorm> 800 works, 1024 fails, 1280 works, 2048 works...
11:51 < AstralStorm> it seems there's some trouble in ALSA calculation of period_time :P
11:52 < AstralStorm> 5333 vs 5334 usec and it's messed up. feel free to close the bug, I'll toss it at ALSA fokls