How does tempo difference works?

[korpe1]

I have difficulties to understand, how does the tempo difference in the Pitch effect works?

I mean PipeWire clients (e.g. Firefox) sends audio streams to the PipeWire server in certain tempo/speed and other clients (e.g. EasyEffects) doesn't have ability to affect that (Firefox does what it want). Now when EasyEffect ask that stream from the server:

• If it start play it at higher tempo the stream will immediately end. You can't play any 1x live stream at 2x speed without this affect.
• If it start play it at lower tempo you have to start keep a buffer, but what when? The buffer will anyway grow too large at the end.

So I think the only way change tempo/speed is that the original source does that.

[wwmm]

If I understood your question correctly you are interested in details about how the plugin implementation does what it does. As I did not write the library and I am not familiar with pitch shifting algorithms implementation I can not answer.

In EasyEffects we use the SoundTouch library https://surina.net/soundtouch/. They are probably in a better position to explain how it is done.

[wwmm]

Out of curiosity I did some tests with the pitch plugin. It isn't a plugin I have a reason to use . Something I've notice is that is adds some amount of latency depending on how we configure it. So it is definitely accumulating data in an internal buffer.

[korpe1]

EasyEffects can't do that because VLC supply audio so slow that EasyEffects hasn't anything to play

EasyEffects does not receive audio buffers directly from the audio application but from PipeWire. The player sends to Pipewire that is the one controlling latency as well as the number of buffers per second that is sent to all the clients.

Yeah, the PipeWire server has a buffer, but how can it solve this problem? I mean the buffer of the server is for inevitable latencies and isn't for adjust the playback speed. Every PipeWire client negotiate buffer and latencies with the server. That buffer is usually less than a second so it isn't help with this when the speed difference is 5 minutes or more.

It is hard to visualize how your example will actually work because there is the audio server in the middle. The one controlling the pace is not the audio player but the clock PipeWire attaches to the node that drives the effects pipeline. Usually the sound card sink.

The player doesn't controll the speed of "stream flow", but it definitely handle the playback speed. Or how VLC can always – regardless of hardware – adjust the playback speed from 0.33x to 2.5x?

[korpe1]

EasyEffects can do with a buffer, but I think it's hard too eventually

EasyEffects does not do buffering. Maybe SoundTouch does it internally. I did not look in detail.

Yeah, EasyEffects is an real-time audio effect machine. And that's why I wonder, how it handle this tempo adjuster? In that comment I just thought the ways it to work.

[korpe1]

Out of curiosity I did some tests with the pitch plugin. It isn't a plugin I have a reason to use . Something I've notice is that is adds some amount of latency depending on how we configure it. So it is definitely accumulating data in an internal buffer.

Do you know, what happens if I use it to decrease the speed for a long time? RAM will running out?
And how this work for increasing the speed? It firstly wait certain time e.g. 10min, then play that buffer 2x speed in 5min and so on?

[wwmm]

Do you know, what happens if I use it to decrease the speed for a long time? RAM will running out?
And how this work for increasing the speed? It firstly wait certain time e.g. 10min, then play that buffer 2x speed in 5min and so on?

Ram won't run out because it isn't just accumulating without sending data ahead. I did not look at the code but it would be bizarre if someone released a library that consumes RAM without bounds.

Based on on my tests yesterday speed increases do not work well if a large percentage is set to the tempo value. It starts to chop sound because of the insertion of silence. Speed increases is probably something that works better when working with files with finite size.