CoreMidi wifi error on iOS
CoreMidi wifi error on iOS
- Subject: CoreMidi wifi error on iOS
- From: Romain Rollet <email@hidden>
- Date: Wed, 10 Apr 2013 12:05:09 +0200
Hello everybody,
I don't know if it is the correct place to post, so please apologize if not.
We are using an application playing midi files on MacOS and sending midi events to an iPod using the network midi facility(aka RTP-Midi). The iOS app synthetises and generates the sounds to an amplifier (e.g. GarageBand or pipe organ apps). Sometime, because of wifi, we have some network packet losses. When we use only one midi channel, no problem, the CoreMidi network stack analyses the RTP-Midi journal and recovers the missing notes. Issue occurs when we use several midi channels within a single RTP-Midi flow. It seems there is a bug in iOS since we have some hanging notes when some packets are losses. We have tested several iOS apps and same results. There is no problem when doing the same thing between two Mac connected with a wifi link, So this is the reason why I suspect the receiving part of iOS CoreMidi stack.
Using the Midi tools app, I dumped the midi messages received by the midi application running on the iOS device. In parallel, I have captured network traffic with wireshark for analysis. Apparently, when some RTP packet are lost, the iOS CoreMidi stack analyses the RTP journal as specified by RFC6295. If only one channel journal (fig.9 of RFC) is present within the journal, no problem, midi NoteOn and NoteOff events are well recovered. If several midi channel journals are present in the journal, then midi NoteOn and NoteOff events are all sent to the midi channel indicated in the first channel journal ! This may explain the hanging note phenomena...
Does anyone experience the same problem ? I have no way to contact Apple about that topic, failed to log to the BugReport website. If somebody can help me.
I am using the latest iOS version (6.1.3) over an iPod Touch.
Best regards,
Romain
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