[linux-audio-dev] jack transport

Paul Davis paul at linuxaudiosystems.com
Sat Mar 19 16:29:57 UTC 2005

>On Fri, Mar 18, 2005 at 11:34:34PM +0100, Jens M Andreasen wrote:
>>  Do jack-transport support SMPTE
>>  Do jack-transport support MIDI song pointer
>>  (guessing yes to above)
>actually i beleive the answer is mostly no, although perhaps
>its best to consider smpte and midi as paralle rather than
>being supported by jack-transport.

correct. SMPTE provides positional sync with a resolution of 1 SMPTE
frame (on the order of 1/30th second) - in other words, appalling for
audio synchronization.

MIDI SPP provides positional sync with a resolution based on a tempo
map. Nice for musical sync, terrible for audio.

>Fons Adriaensen was working on this. Theoretically, smpte lock
>between 2 stable systems could be quite tight, but not only is
>it not as tight as Jack, it is way too complicated and cpu intensive.

not entirely true. using a DLL for this is not very expensive and can
be rather accurate. but you are right that it still cannot provide
sample level sync.

>the reason i asked about jack-transport in relation to bio2jack
>is that there are several unasked question on the mplayer lists
>re how to get this working.  People dont realise that bio2jack
>only provides "jack 1.0 simple" or whatever you want to call it.

but thats for a very obvious reason: there is nothing in any of the
blocking i/o models that bio2jack is there to assist with that
corresponds to the notion of a transport model. what OSS or ALSA calls
would an application be making to do something like this? answer:
none. therefore, bio2jack doesn't so much provide "jack 1.0 simple" as
"blocking i/o via JACK". if you want transport stuff, you need an API
that has no analog in OSS or ALSA. AFAIK, for Linux at least, JACK is
the only API that provides such a concept.


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