I know this is now a very old thread, but I would like to complete it by saying that the bug seems to be resolved in Ardour 4.
$ uname -a
Linux home 3.18.13-rt10whoff1 #1 SMP PREEMPT RT Wed May 27 20:31:10 EDT 2015 x86_64 x86_64 x86_64 GNU/Linux
$ /opt/Ardour-4.0.0/bin/ardour4 -v
bind txt domain [gtk2_ardour4] to /opt/Ardour-4.0.0/share/locale
Ardour4.0.0 (built using 4.0 and GCC version 4.4.7)
$ sndfile-info Audio\ 1-1.w64 # a w64 that was still being written to.
Version : libsndfile-1.0.25
========================================
File : Audio 1-1.w64
Length : 13080985744
riff : 0 (should be 13080985744)
wave
fmt : 48
Format : 0x3 => WAVE_FORMAT_IEEE_FLOAT
Channels : 1
Sample Rate : 96000
Block Align : 4
Bit Width : 32
Bytes/sec : 384000
fact : 32
frames : 0
data : 24
*** Unknown chunk marker : 481185. Exiting parser.
Sample Rate : 96000
Frames : 3270246400
Channels : 1
Format : 0x000B0006
Sections : 1
Seekable : TRUE
Duration : 09:27:45.067
I was able to record longer than the 6 hours and some minutes as was documented before. It is clear that this bug seems resolved by comparing:
$ sndfile-info Audio\ 1-1.w64
…snip
File : Audio 1-1.w64
Length : 13080985744
…snip
and
$ sndfile-info Audio\ 1-1.w64
…snip
File : Audio 1-1.w64
Length : 8589934736
…snip
From the most recent test, and one of the earlier tests, respectively.
Thank you for all that you do.
Will