Manage INVALID HANDLE channel correctly

FMOD Engine
1

Hi,

Here is my scenario:
First I call playSound, this creates a ‘Channel* chan’ object.
Let’s say after a few seconds, I want to modify something on ‘chan’ ( modify frequency, fade out, stop … ).
My concern is that if the sound has already finished playing it seems FMOD will automatically delete the ‘chan’ object. And all my calls on ‘chan’ will return error with ‘FMOD_ERR_INVALID_HANDLE’.

My questions:
When I use my invalid ‘chan’ handle. Does FMOD means:
“I know this is a channel handle that has stopped, so I won’t modify it”
or
“I don’t know what ‘chan’ is, it musn’t be used in the API anymore”.
in other words, is it illegal to use an invalid ‘chan’ ( like using a deleted object in C++ ) ?

If it’s illegal, what’s the easiest way to track if my ‘chan’ is still valid, I need a way to set it to ‘nullptr’ when FMOD deletes it internally.

Thanks

2

Hi,

I’m relatively new to FMOD too and found this confusing as well.

I mention here about using ChannelControl::setCallBack() to get a callback when the sound ends so maybe that works for you. As I mentioned, I am still trying to figure out why it is not firing when iOS is in background mode.

3

Thanks for the reply -
yes I had the idea of adding callback for each sounds I wanted to track. but that feel a bit over-engineered. I hope there is something simpler

4

Hi,

I will link to our white papers that outline our handle system: FMOD API | White Papers - Handle System. In summary, it is closest to your first answer but not exactly. As it says in our docs “If a Channel is stopped with ChannelControl::stopor ends naturally, the Channel handle will become invalid and return FMOD_ERR_INVALID_HANDLE” so it will be safe to still interact with it however, it will just return an invalid handle. A way to check if a channel is still valid is using the channel in an FMOD function and checking the result for FMOD_ERR_INVALID_HANDLE.

Hope this clears it up a bit.

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5

Thanks for the detail.
So my understanding is that on my app side, I don’t need to track the life time of all my channel handles. There is no risk of undefined behavior when using an invalid one.
That makes my developer life easier.

6

Correct, if a stopped channel is used in an FMOD function it will return the FMOD_RESULT FMOD_ERR_INVALID_HANDLE.

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7

Thanks for the confirmation

1 Like