[LAA] JACK 0.124.0 released

Paul Davis paul at linuxaudiosystems.com
Wed Jan 22 19:31:50 UTC 2014

The small but intrepid group of JACK 1 developers announce the release
today of JACK 0.124.0, the latest version of JACK 1. This release features
3 major new features that are designed to make JACK easier to use and
better in several ways, along with a large set of minor bug fixes and
improvements. You can fetch the tarball release
It has been tagged in the JACK 1 git repository as "0.124.0".

 One of the "minor" bug fixes will make a huge difference for some users:
if a particular JACK client crashes *only* the misbehaving client will be
"zombified" - other clients will continue functioning normally (after a
short delay). If you are developing JACK applications, this can make a huge
difference to your day-to-day experience of JACK 1. The Metadata API

It is now possible to define arbitrary metadata to be associated with any
JACK port or JACK client. This API lays the groundwork for more useful
naming of ports and clients (particularly those associated with hardware),
as well as many other features that developers have talked about in a JACK
context for several years. The full docs on the API can be found
there is also a man page for
jack_property, which is the primary command line tool for setting, removing
and changing metadata. A short tutorial <http://jackaudio.org/metadata> on
using the Metadata API is available.
Builtin MIDI hardware I/O (on Linux)

For years, we have known that the performance of the -X seq and -X raw
options to the ALSA backend have left much to be desired. For that reason,
most users have been instructed to use a2jmidid (typically with the -e flag
to tell it use external (hardware) MIDI devices). Although
a2jmididprovided good MIDI I/O, it has two problems:

   1. Requires starting an addition program in order to get MIDI I/O via
   hardware working
   2. Adds latency to the MIDI I/O "through" or "monitor" signal pathway

 This release of JACK 1 sees the transformation of a2jmidid into a "slave"
driver that can be started as a part of JACK, much like the old -X seq and
-X raw options. This not only removes the need to start a separate program,
but also reduces the "through" or "monitoring" latency of MIDI I/O by 1
JACK period.

The canonical way to invoke this new internal MIDI driver is with -X
alsa_midi, which will create JACK ports for all MIDI devices (and other
MIDI applications) known to ALSA at the time that JACK starts up. Note that
the new internal driver does not currently notice the arrival or departure
of MIDI hardware or applications, but future improvements will correct

In addition, the old -X seq and -X raw implementations have been removed.
However, using -X seq will be interpreted as a request to use the new
internal MIDI driver, and so is formally equivalent to using -X alsa_midi.
Note that -X seq is an argument to the ALSA backend, and so comes
*after*the backend specification; by contrast, -X
alsa_midi is a server argument, and must come before the backend

It is worth noting that the server argument -X alsa_midi can be used with
any Linux-based backend (ALSA, OSS, Dummy, Netjack) to get the ALSA MIDI
bridge functional.
Builtin Internal Client for using additional ALSA devices

Older versions of JACK have come with the tools alsa_in and alsa_out which
can be used to add additional ALSA supported audio devices to a running
JACK setup. These tools work quite well, but:

   1. Fons Adriennsen developed significantly better versions known as
   zita-a2j and zita-j2a that use his own resampler.
   2. these tools are (like the rest of the JACK tools) separate programs
   that the user must start up after the server is running

 To address these two points, the zita-a2j/zita-j2a code has been merged
into the tools part of JACK as a pair of *internal* clients ("zalsa_in" and
"zalsa_out") that can be specified on the command line. So for example,
this JACK command line:

	jackd ... -I "USB Mic:zalsa_in/-dhw:USB,-r44100,-n2,-p512" ...

will create an internal client called "USB Mic" that represents the ALSA
device "hw:USB" using the ZITA alsa/jack bridge code, running at 44100kHz,
with 2 periods of size 512. If you do not specify the period size or sample
rate, then the values in use by the backend will be adopted. Audio being
captured or played back via devices added to JACK in this way will be
resampled with substantial accuracy and quality.

Note that the -I argument has been present in JACK 2 for sometime, but the
new JACK1 implementation extends the semantics of its argument by allowing
the user to specify a client name as well as arguments for the internal
client code.

Both internal clients (zalsa_in and zalsa_out) will accept the -h argument
to show their possible arguments: jackd -I zalsa_in/-h -d alsa (the final -d
alsa is required by JACK but not used in this case). The arguments will
match those of the standalone zita-a2j and zita-j2a (external) clients.

Since this new "multiple device" capability is implemented using JACK
internal clients, you can remove a given device by just unloading the
client using the long-existing but rarely used jack_unload command.
Similarly, if you wanted to add a device to a running server after it has
started, jack_load can be used for that.

It is worth noting that these internal clients can be used with any
Linux-based backend (ALSA, FFADO, OSS, Dummy, Netjack) to add additional
ALSA-support devices to an instance of JACK.
Syntactic Sugar Version

To make the addition of extra audio devices to an instance of JACK even
easier, JACK 1 also features the new -A option which takes almost nothing
more than an ALSA card name (e.g. "SB", "DSP", "Codec", "HDMI" and many
others) and makes the device available for playback or capture or both.
Adding %p or %c to the card name limits the direction of audio flow.

This option does nothing more than translate its argument into an
equivalent use of -I, so for example:

	-A SB

is equivalent to using *both* of these arguments:

	-I SB/zalsa_in/-dhw:SB
	-I SB/zalsa_out/-dhw:SB

As with -I, the -A argument may be used multiple times to add as many
devices as you want. -A is simple but not very powerful - if you need to
provide more options (e.g. to adjust I/O latency values), then you must use
the -I argument instead.

Finally, note that these internal clients are theoretically compatible with
JACK 2, and should work with that implementation of JACK once JACK 2 has a
working internal client loading mechanism restored.
Complete Change List for 0.124.0 Major New Features

   - add the new metadata API, allowing arbitrary metadata to be associated
   with JACK ports and clients
   - merge a2jmidid code into JACK as (slave) driver.
   - add zita-a2j as internal clients

Notable Source Code Rearrangements

   - Use separated JACK public headers and tools repositories, in an
   attempt to share these with JACK 2
   - JACK 1 now requires the Berkeley DB library to build (this is used
   inside the metadata API implementation)
   - The new ZITA-based internal clients are optional - to build them you
   will need Fons Adriennsen's ALSA PCMI and ZITA resampler libraries

Bug Fixes, Updates and Other Enhancements

   - Install jslist.h with JACK headers since it is used by control.h
   - clarify use of alsa_in/alsa_out's -q parameter
   - check for engine->driver before delivery latency events to its
   internal client
   - the default error callback no longer calls DEBUG, which breaks if
   _jack_get_microseconds has not been set
   - remove all references to MMX/MME (which was never used within JACK)
   - remove --enable-ensure-mlock configure option
   - deprecate jack_thread_wait() as done in JACK2
   - clean up client code to fix inconsistent handling of the return value
   from the process callback
   - improve configure.ac for use on OS X
   - redesign thread calls to make them work correctly on OS X
   - remove port.g from documentation since it is not a public header
   - remove timestamps code, since it was no longer used or useful.
   - fix detection of libsamplerate
   - support setbufsize now available in firewire driver
   - improved jack_get_cycle_times() and improved DLL implementation
   (particularly after freewheeling)
   - compile with FFADO versions < 9 once more
   - update FFADO latencies after setbufsize
   - use max (JACK_CLIENT_EVENT_TIMEOUT,command-line-client-timeout) for
   poll on event handling when in non-RT mode
   - tidy up error messages when something goes wrong with client event
   - add a latency callback to the ALSA backend, and ensure that the
   backend's latency callback, if it exists, is called after a buffer size
   - provide FFADO/firewire backend with its own latency callback
   - adjust driver/backend port latencies for both playback and capture
   ports in both directions
   - handle latency callbacks before graph reorder callbacks, as per a
   recent (correct) change in JACK 2
   - handled failed malloc caused limits.conf being changed while jackd is
   - Correctly recognize ALSA subdevices when symbolic names like hw:Live
   are used.
   - If an attempt to reconfigure the ALSA backend fails, it will fall back
   to its previous successful configuration.
   - remove watchdog thread from engine/jackd, since Linux no longer allows
   SCHED_{FIFO,RR} tasks to take over the cpu unless the user misconfigures a
   very obscure part of their system configuration
   - fix delivery of buffer size changes to internal clients
   - fix incorrect memset() of an event in latency handling
   - fix arguably incorrect marking of client with errors after process
   cycle fails to return to server
   - use a default size of 2048 byte for MIDI port buffers, like JACK 2, to
   avoid problems with MIDI delivery under fairly common circumstances
   - add -I option to command line to allow loading internal clients
   (consistent with JACK 2), though with more complex argument style to -I to
   permit client names and arguments


Jonathan Woithe, Adrian Knoth, Fons Adriennsen, Nedko Arnaudov, Torben
Hohn, Paul Davis.

Thanks to David Robillard, Jonathan Liles and Filipe Coehlo for their
participation in the design of the metadata API.
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