From b1462c127aa213fa04d945b75146789e6a7d4674 Mon Sep 17 00:00:00 2001
From: Matthew Clark <matthew1000@gmail.com>
Date: Mon, 26 Mar 2018 11:08:07 +0100
Subject: [PATCH] More audio mixing examples

---
 README.md |  4 ++--
 basics.md | 12 ++++++++++++
 mixing.md | 29 +++++++++++++++++++++++++++--
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 7a0cfcd..94d9a85 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,7 @@ A few Python examples are also included for when you need GStreamer to be dynami
 ## Sources and references
 
 * [Basic command line reference](http://docs.gstreamer.com/display/GstSDK/Basic+tutorial+10%3A+GStreamer+tools)
-* [More examples here](http://docs.gstreamer.com/display/GstSDK/gst-launch)
+* [Pipeline examples](https://gstreamer.freedesktop.org/documentation/tools/gst-launch.html#pipeline-examples)
 * [List of all Gstreamer plugins](https://gstreamer.freedesktop.org/documentation/plugins.html)
 * [Handy elements](https://gstreamer.freedesktop.org/documentation/tutorials/basic/handy-elements.html#uridecodebin)
 
@@ -27,7 +27,7 @@ A few Python examples are also included for when you need GStreamer to be dynami
 * https://github.com/xmementoit/gstreamerCheatsheet/blob/master/README.md
 * https://gist.github.com/nebgnahz/26a60cd28f671a8b7f522e80e75a9aa5
 
-## Interaction
+## Interacting with the GStreamer pipeline
 
 If you want to interact with GStreamer after it's started (e.g. respond to an event, or dynamically change a pipeline), the command-line GStreamer doesn't really cut it. Instead you have two options:
 
diff --git a/basics.md b/basics.md
index e2ba51c..344090f 100644
--- a/basics.md
+++ b/basics.md
@@ -109,6 +109,18 @@ gst-launch-1.0 filesrc location=$SRC ! \
     autovideosink
 ```
 
+### Play an MP3 audio file
+
+Set the environment variable `$AUDIO_SRC` to be the location of the MP3 file. Then:
+
+```
+# All three of these do the same thing:
+gst-launch-1.0 playbin uri=file://$AUDIO_SRC
+gst-launch-1.0 -v uridecodebin uri="file://$AUDIO_SRC" ! autoaudiosink
+gst-launch-1.0 -v filesrc location=$AUDIO_SRC ! mpegaudioparse ! decodebin ! autoaudiosink
+```
+
+
 ### Play files back to back
 
 See (https://coaxion.net/blog/2014/08/concatenate-multiple-streams-gaplessly-with-gstreamer/)[https://coaxion.net/blog/2014/08/concatenate-multiple-streams-gaplessly-with-gstreamer/]
diff --git a/mixing.md b/mixing.md
index 972e4d7..c05f681 100644
--- a/mixing.md
+++ b/mixing.md
@@ -93,10 +93,35 @@ gst-launch-1.0   \
 
 Use the `audiomixer` element to mix audio. It replaces the `adder` element, which struggles under some circumstances (according to the [GStreamer 1.14 release notes](https://gstreamer.freedesktop.org/releases/1.14/)).
 
-Mix to audio streams:
+### Mix two (or more) test streams
 
 ```
-gst-launch-1.0 audiotestsrc freq=100 ! audiomixer name=mix ! audioconvert ! alsasink audiotestsrc freq=500 ! mix.
+gst-launch-1.0 \
+    audiomixer name=mix !  audioconvert ! autoaudiosink \
+    audiotestsrc freq=400 ! mix. \
+    audiotestsrc freq=600 ! mix.
 ```
 
+### Mix two test streams, dynamically
+
 [This Python example](python_examples/audio_dynamic_add.py) shows a dynamic equivalent of this example - the second test source is only mixed when the user presses Enter.
+
+### Mix two (or more) MP3 files
+
+```
+gst-launch-1.0 \
+    audiomixer name=mix !  audioconvert ! autoaudiosink \
+    filesrc location=$AUDIO_SRC  ! mpegaudioparse ! decodebin ! mix. \
+    filesrc location=$AUDIO_SRC2 ! mpegaudioparse ! decodebin ! mix.
+```
+
+### Mix a test stream with an MP3 file
+
+Because the audio streams are from different sources, they must each be passed through `audioconvert`.
+
+```
+gst-launch-1.0 \
+    audiomixer name=mix ! audioconvert ! autoaudiosink \
+    audiotestsrc is-live=true freq=400 ! audioconvert ! mix. \
+    filesrc location=$AUDIO_SRC ! mpegaudioparse ! decodebin ! audioconvert ! mix.
+```