Add a fade in to stream playback on start #107557
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AThousandShips
changed the title
AThousandShips
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bug
topic:audio
cherrypick:4.4
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After doing some test with sounds with a punchy start, it revealed this PR cannot be merged as-is. If this were to get in godot, it should be an option, because it's too destructive for the start of some punchy sounds. Here's an example: no fade in: no_fade_in.mp4with fade in: with_fade_in.mp4note that this example is just godot playing samples one after the other with a 1.5s interval |
v1993
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Jun 18, 2025
| @@ -462,8 +462,8 @@ void AudioServer::_mix_step() { | |||
| // The channels correspond to output channels of the audio device, e.g. stereo or 5.1. To reduce needless nesting, this is done with a helper method named `_mix_step_for_channel`. | |||
| for (int channel_idx = 0; channel_idx < channel_count; channel_idx++) { | |||
| AudioFrame *channel_buf = thread_get_channel_mix_buffer(bus_idx, channel_idx); | |||
| // TODO: This `fading_out` check could be replaced with with an exponential fadeout of the samples from the lookahead buffer for more punchy results. | |||
| if (fading_out) { | |||
| // TODO: This `fading` check could be replaced with with an exponential fadeout of the samples from the lookahead buffer for more punchy results. | |||
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Suggested change
| // TODO: This `fading` check could be replaced with with an exponential fadeout of the samples from the lookahead buffer for more punchy results. | |
| // TODO: This `fading` check could be replaced with with an exponential fade of the samples from the lookahead buffer for more punchy results. |
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This is a simple attempt to fix #107551
I used the same behaviour used for the fade out mechanism to add a fade in mechanism. This just takes advantage of the cubic interpolation to smooth the start, just like it does for the stop.
Without interpolation on start:
audioloopclick.mp4
With interpolation on start:
audioloopnoclick.mp4
Problems
This doesn't work well with sounds with a punchy start, and should only be an option you set for streams. A comment below shows why.
Potential enhancements
Because of the problem above, this could be used only for looping streams, or added as a stream parameter (the playback state would just need to be set to
PLAYINGinstead ofFADE_INif it's not a looping stream). I'm just not really sure how to do it properly in this case.