Remove audio samples in favor of Oboe's repo.

We shouldn't be recommending OpenSLES any more, and we don't need Oboe
samples because Oboe's own samples are much more thorough than ours will
ever be.

Author: DanAlbert

audio-echo/README.md

@@ -1,77 +1,6 @@
-# Audio-Echo
+# Sample removed
 
-The sample demos how to use OpenSL ES to create a player and recorder in Android
-Fast Audio Path, and connect them to loopback audio. On most android devices,
-there is a optimized audio path that is tuned up for low latency purpose. The
-sample creates player/recorder to work in this highly optimized audio
-path(sometimes called native audio path,
-[low latency path](http://stackoverflow.com/questions/14842803/low-latency-audio-playback-on-android?rq=1),
-or fast audio path).
+This sample has been removed because the API it demonstrated (OpenSLES) is
+deprecated. New apps should instead use [Oboe], which has its own samples.
 
-***Note that OpenSL ES is
-[deprecated from Android 11](https://developer.android.com/preview/features#deprecate-opensl),
-developers are recommended to use [Oboe](https://github.com/google/oboe) library
-instead.***
-
-## Usage
-
-App will capture audio from android devices and playback on the same device; the
-playback on speaker will be captured immediately and played back...! So to
-verify it, it is recommended to "mute" the playback audio with a
-earspeaker/earphone/earbug so it does not get looped back. Some device like
-Nexus 9, once you plug in an external headphone/headspeaker, it stops to use
-onboard microphone AND speaker anymore -- in this case, you need turn on the
-microphone coming with your headphone. Another point, when switching between
-external headphone and internal one, the volume is sometimes very low/muted;
-recommend to increase the playback volume with volume buttons on the phone/pad
-after plugging external headphone.
-
-## Low Latency Verification
-
-1. execute "adb shell dumpsys media.audio_flinger". Find a list of the running
-   processes
-
-   Name Active Client Type Fmt Chn mask Session fCount S F SRate L dB R dB
-   Server Main buf Aux Buf Flags UndFrmCnt\
-   F 2 no 704 1 00000001 00000003 562
-   13248 S 1 48000 -inf -inf 000033C0 0xabab8480 0x0 0x600 0\
-   F 6 yes 9345 3
-   00000001 00000001 576 128 A 1 48000 0 0 0376AA00 0xabab8480 0x0 0x400 256
-
-1. execute adb shell ps | grep echo
-
-- find the sample app pid
-- check with result on step 1.\
-  if there is one "F" in the front of your echo
-  pid, **player** is on fast audio path\
-  For fast audio capture \[it is totally
-  different story\], if you do **NOT** see\
-  com.example.nativeaudio
-  W/AudioRecord﹕ AUDIO_INPUT_FLAG_FAST denied by client\
-  in your logcat output
-  when you are creating audio recorder, you could "assume" you are on the fast
-  path.\
-  If your system image was built with muted ALOGW, you will not be able
-  to see the above warning message.
-
-## Tune-ups
-
-A couple of knobs in the code for lower latency purpose:
-
-- audio buffer size
-- number of audio buffers cached before kicking start player The lower you go
-  with them, the lower latency you get and also the lower budget for audio
-  processing. All audio processing has to be completed in the time period they
-  are captured / played back, plus extra time needed for:
-- audio driver
-- audio flinger framework,
-- bufferqueue callbacks etc Besides those, the irregularity of the buffer queue
-  player/capture callback time is another factor. The callback from openSL may
-  not as regular as you assumed, the more irregularity it is, the more likely
-  have choopy audio. To fight that, more buffering is needed, which defeats the
-  low-latency purpose! The low latency path is highly tuned up so you have
-  better chance to get more regular callbacks. You may experiment with your
-  platform to find the best parameters for lower latency and continuously
-  playback audio experience. The app capture and playback on the same device
-  \[most of times the same chip\], capture and playback clocks are assumed
-  synchronized naturally \[so we are not dealing with it\]
+[Oboe]: https://github.com/google/oboe