Subject: Re: [linux-audio-dev] Introducing DMIDI
From: martijn sipkema (msipkema_AT_sipkema-digital.com)
Date: Wed Dec 19 2001 - 21:53:57 EET
> >RTP timestamps are used for this.
>
> Sure, it may be used for this but it isn't: MIDI events are played at
reception time. In MWPP for example, the timestamp is only used to determine
wether a packet is too late or not.
oh, well it should be used for that, doesn't need to be in the protocol
probably. as long
as there is a timestamp the receiving end can use it to avoid jitter.
> >I think a protocol for realtime MIDI over UDP will always have
significant
> >protocol overhead, I
> >don't see this as a problem however.
>
> Considering a 44 bytes overhead (IP + UDP) + the 4 DMIDI header bytes
intended to address a specific node and device, sending a full MIDI data
flow (about 1000 3-bytes events per second) requires nearly 400 kbs when the
MIDI rate is 31.25 kbs. It's not a problem as long as the corresponding
bandwith is available to you. But if you plan to address different devices
on the same node (for example using a multiport interface), you should be
able to provide each device with an equivalent full MIDI data flow and then
the problem seriously increases with the number of devices.
normally the full midi bandwidth isn't used except when doing a sysex dump.
if events are to be
scheduled at exactly the same time they could probably be in the same
packet. if not then the
RTP timestamp can not be used. when transmitting realtime one doesn't know
the events ahead
of time so they cannot be combined anyway. for very low bandwidth links
compression could be
used on top of the protocol.
--martijn
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