# Mixing (GStreamer command-line cheat sheet)

Page contents:

* Mixing video (i.e. replacing or overlaying)
* Mixing audio (i.e. replacing or merging audio tracks)
* Mixing video & audio together

## Mixing video

The element `compositor` allows video to be mixed (overlayed, put side-by-side, etc).

The older `videomixer` element can be used instead, and takes the same arguments as `compositor` so it's easy to swap between them. However, `videomixer` is apparently inferior in some situations, such as for live streams.

### Picture in picture

Here we have two source (mp4) files, which should be set as environment variables `$SRC` and `$SRC2`

```
gst-launch-1.0   \
    filesrc location="$SRC2" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=640,height=360 ! \
    compositor name=mix sink_0::alpha=1 sink_1::alpha=1 !   \
    videoconvert ! autovideosink \
    filesrc location="$SRC" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=320,height=180! \
    mix.
```

Put a box around the in-picture using `videobox` e.g.

```
gst-launch-1.0   \
    filesrc location="$SRC2" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=640,height=360 ! \
    compositor name=mix sink_0::alpha=1 sink_1::alpha=1 !   \
    videoconvert ! autovideosink \
    filesrc location="$SRC" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=320,height=180! \
    videobox border-alpha=0 top=-10 bottom=-10 right=-10 left=-10 ! \
    mix.
```

Choose where the in-picture goes with the ‘xpos’ and ‘ypos’ attributes of videomixer, e.g.

```
gst-launch-1.0   \
    filesrc location="$SRC2" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=640,height=360 ! \
    compositor name=mix sink_0::alpha=1 sink_1::alpha=1 sink_1::xpos=50 sink_1::ypos=50 !   \
    videoconvert ! autovideosink \
    filesrc location="$SRC" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=320,height=180! \
    mix.
```

Add audio by demuxing the inputs so it can be handled separately. This example does so on the first source (rather than mixing the two together):

```
gst-launch-1.0   \
    filesrc location="$SRC" ! \
    qtdemux name=demux  demux.audio_0 ! queue ! decodebin ! audioconvert ! audioresample ! \
    autoaudiosink \
    demux.video_0 ! queue ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=640,height=360 ! \
    compositor name=mix sink_0::alpha=1 sink_1::alpha=1 sink_1::xpos=50 sink_1::ypos=50 !   \
    videoconvert ! autovideosink \
    filesrc location="$SRC2" ! \
    decodebin ! videoconvert ! \
    videoscale ! video/x-raw,width=320,height=180! \
    mix.
```

### Compositor with just one source

It is possible for a compositor to have just one source. This example has the test source of a bouncing ball. It also has the audio test source included (muxed).

```
gst-launch-1.0   \
    videotestsrc pattern=ball ! \
    decodebin ! \
    compositor name=mix sink_0::alpha=1 ! \
    x264enc ! muxer. \
    audiotestsrc ! avenc_ac3 ! muxer. \
    mpegtsmux name=muxer ! queue ! \
    tcpserversink host=127.0.0.1 port=7001 recover-policy=keyframe sync-method=latest-keyframe sync=false
```

## Mixing audio

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 two (or more) test audio streams

Here we use two different frequencies (tones):

```
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

Ensure `$AUDIO_SRC` and `$AUDIO_SRC2` environment variables are set to 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.
```

## Mixing video & audio together

### Mix two fake video sources and two fake audio Sources

We use `compositor` to mix the video and `audiomixer` to mix the audio.

This example combines two test video inputs and also two test audio inputs:

```
gst-launch-1.0 \
    compositor name=videomix ! autovideosink \
    audiomixer name=audiomix !  audioconvert ! autoaudiosink \
    videotestsrc pattern=ball ! videomix. \
    videotestsrc pattern=pinwheel ! videoscale ! video/x-raw,width=100 ! videomix. \
    audiotestsrc freq=400 ! audiomix. \
    audiotestsrc freq=600 ! audiomix.
```

The output looks like:

![Pinwheel and ball](images/pinwheel_and_ball.png "Pinwheel and ball")

The above example is simple because we didn't have to split or combine the audio and video.
This example muxes the mixed audio & video together, and then outputs via TCP.

```
# View this in VLC with tcp://localhost:7001
gst-launch-1.0 \
    mpegtsmux name=mux ! \
    tcpserversink port=7001 host=0.0.0.0 recover-policy=keyframe sync-method=latest-keyframe sync=false \
    compositor name=videomix ! x264enc ! queue2 ! mux. \
    audiomixer name=audiomix !  audioconvert ! audioconvert ! audioresample ! avenc_ac3 ! queue2 ! mux. \
    videotestsrc pattern=ball ! videomix. \
    videotestsrc pattern=pinwheel ! videoscale ! video/x-raw,width=100 ! videomix. \
    audiotestsrc freq=400 ! audiomix. \
    audiotestsrc freq=600 ! audiomix.
```

### Mix a AV file with fake video and audio

This one puts a bouncing ball in the corner of a file:

```
gst-launch-1.0 \
    compositor name=videomix ! autovideosink \
    audiomixer name=audiomix !  audioconvert ! autoaudiosink \
    filesrc location=$SRC ! qtdemux name=demux \
    demux.video_0 ! queue2 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=360 ! videomix. \
    demux.audio_0 ! queue2 ! decodebin ! audioconvert ! audioresample ! audiomix. \
    videotestsrc pattern=ball ! videoscale ! video/x-raw,width=100,height=100 ! videomix. \
    audiotestsrc freq=400 volume=0.1 ! audiomix.
```

and this one also muxes the video and audio together to be sent over TCP:

```
# View this in VLC with tcp://localhost:7001
gst-launch-1.0 \
    mpegtsmux name=mux ! \
    tcpserversink port=7001 host=0.0.0.0 recover-policy=keyframe sync-method=latest-keyframe sync=false \
    compositor name=videomix ! x264enc ! queue2 ! mux. \
    audiomixer name=audiomix !  audioconvert ! audioconvert ! audioresample ! avenc_ac3 ! queue2 ! mux. \
    filesrc location=$SRC ! qtdemux name=demux \
    demux.video_0 ! queue2 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=360 ! videomix. \
    demux.audio_0 ! queue2 ! decodebin ! audioconvert ! audioresample ! audiomix. \
    videotestsrc pattern=ball ! videoscale ! video/x-raw,width=100,height=100 ! videomix. \
    audiotestsrc freq=400 volume=0.1 ! audiomix.
```

This one uses `uridecodebin` which allows a wider range of inputs to be added:

```
gst-launch-1.0 \
    compositor name=videomix ! autovideosink \
    audiomixer name=audiomix !  audioconvert ! autoaudiosink \
    uridecodebin uri=file://$SRC name=demux ! \
    queue2 ! audioconvert ! audioresample ! audiomix. \
    demux. ! queue2 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=360 ! videomix. \
    videotestsrc pattern=ball ! videoscale ! video/x-raw,width=100,height=100 ! videomix. \
    audiotestsrc freq=400 volume=0.1 ! audiomix.
```

And again, here's a version that muxes again to send to TCP:

```
# View this in VLC with tcp://localhost:7001
gst-launch-1.0 \
    mpegtsmux name=mux ! \
    tcpserversink port=7001 host=0.0.0.0 recover-policy=keyframe sync-method=latest-keyframe sync=false \
    compositor name=videomix ! x264enc ! queue2 ! mux. \
    audiomixer name=audiomix ! audioconvert ! audioresample ! avenc_ac3 ! queue2 ! mux. \
    uridecodebin uri=file://$SRC name=demux ! \
    queue2 ! audioconvert ! audioresample ! audiomix. \
    demux. ! queue2 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=360 ! videomix. \
    videotestsrc pattern=ball ! videoscale ! video/x-raw,width=100,height=100 ! videomix. \
    audiotestsrc freq=400 volume=0.2 ! audiomix.
```

### Mix two AV files

This does picture-in-picture, with the audio from both files included.

```
gst-launch-1.0 \
    compositor name=videomix ! autovideosink \
    audiomixer name=audiomix !  audioconvert ! autoaudiosink \
    uridecodebin uri=file://$SRC name=demux1 ! \
    queue2 ! audioconvert ! audioresample ! audiomix. \
    demux1. ! queue2 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=360 ! videomix. \
    uridecodebin uri=file://$SRC2 name=demux2 ! \
    queue2 ! audioconvert ! audioresample ! audiomix. \
    demux2. ! queue2 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=320,height=180 ! videomix.
```