Alternative way to reproduce this issue with the integrated cast functionality:
- select ... -> Cast -> Cast Desktop 
- Choose Chromecast device in network, make sure "Share Audio" is checked in the dialog window.
- Play some audio on the system

What went wrong:
Audio is NOT mirrored to the Chromecast device. 

This also worked on older CrOS versions. 

Additional note: this issue also reproduces on current CrOS dev (55.0.2883.17)

Also reproduces on 56.0.2905.0 dev (Platform 8953.0.0 (Official Build) dev-channel veyron_minnie)

Also reproduces on a chrome book. With automatic updates I even cannot roll back to a previous version.
The text-to speach API works really well on chrome, but I cannot record the sound with screencastify which is really annoying...

what the hell!!!!!! im mad as fuck

George, can you please take a look?

Sorry, should have been Qiang

Once upon a time, I fixed a bug that the computer is not muted during audio sharing. 

At that time, I tested, after muting (at system level), the sharing still works well.

One possibility is that CrOS now does not give us the audio stream if we mute the audio at system level. If that's the case, then I will have to revert the previous fix.

I'll take a deeper look.

Update:

It is as I expected. If we mute the system audio level, then we are going to get nothing, but previously, we can get the pre-mute audio stream.

niklase@: Do you know anyone we can follow up with on CrOS side? I am not sure whether this is a CrOS bug or by design. 

cc dgreid for #12, could be an optimization

cychiang: Did something change that would mute the system audio before it gets to the loopback device?

Re #14: Not that case. 

It is the chrome browser that actively calls "cras_client_set_system_mute(client_, 1);" before capturing the system audio. (As in one use case we hope that the sender side is mute, and only play out the stream on the receiver side)
Previously, we found it works, we can still capture the audio stream even if the speaker is mute on the sender side. But now nope, we get nothing.

Update: 

I can also reproduce the issue even if we do not mute the sender speaker.
About 90% probability, we cannot capture any system audio, though a slim chance that we can capture the data.

From my code reading and testing:
After CrasInputStream::Start() [1] is called, the callback CrasInputStream::SampleReady is never triggered by CrOS.

Can some one take a look at the function [1], is there anything we miss setting for system audio capturing?

[1]https://cs.chromium.org/chromium/src/media/audio/cras/cras_input.cc?q=SamplesReady&sq=package:chromium&dr=C&l=134

Looks good on 9134.0.0 image.
I will test previous versions.

Might be this one  https://bugs.chromium.org/p/chromium/issues/detail?id=657510
The fix is not merged to R55. I will check it.

With this fix on R55, https://chromium-review.googlesource.com/#/c/415848/
Chromecast and demo app in #0 works fine.

We need to merge it back to R55.

Hi Bernie, I would like to merge CL in #20 to R55. Currently, CrOS can not cast audio to ChromeCast, it is very annoying for users. Thanks!

Given this landed a while back, and is a small change we can land it on 55 however that may be moot, we are not planning further 55 stable pushes (last one is being tested today). So this is likely to not get out to users on stable until 56 (end of the month). 

https://chromium-review.googlesource.com/#/c/425530/ merged

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 Issue 664818  has been merged into this issue.