kern/52075: /dev/audio mangles multi-track MIDI output

[idleroux%fastmail.fm@localhost]

>Number:         52075
>Category:       kern
>Synopsis:       /dev/audio mangles multi-track MIDI output
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Mar 15 01:15:00 +0000 2017
>Originator:     Ian D. Leroux
>Release:        NetBSD 7.99.60
>Organization:
>Environment:
NetBSD scrameustache.unrouted.net 7.99.60 NetBSD 7.99.60 (GENERIC) #0: Tue Feb 21 18:09:13 EST 2017  idleroux%scrameustache.unrouted.net@localhost:/build/obj/sys/arch/amd64/compile/GENERIC amd64
>Description:
On recent -CURRENT, when playing a multi-track MIDI file with audio/timidity, every note played is abruptly cut off as soon as another note (possibly on another track) is played.  Chords, in particular, get reduced to the bottom-most note (since the lowest part is typically the last one in the file), with a glitch at the start as the other notes are interrupted immediately after being played. This behaviour is not observed with 7.99.29, so it was introduced sometime in the last year.  It sounds as though something has changed in the handling of multiple samples sent to a single OSS output channel.

Note that no sound daemon is running, timidity is playing directly to /dev/audio.


>How-To-Repeat:
Install audio/timidity and audio/eawpatches from pkgsrc.
Download a MIDI file with more than one track
(e.g. https://upload.wikimedia.org/wikipedia/en/5/5f/Linear_counterpoint_from_Stravinsky%27s_Octet.mid ),
renaming it to test.mid

# First, demonstrate correct output
# by converting in software.
$ timidity -Ow test.mid
$ audioplay test.wav

# Then demonstrate the problem
$ timidity test.mid
>Fix: