Example launch line

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gst-launch-1.0 -v -m audiotestsrc ! audioconvert ! audio/x-raw,format=S8,channels=2 ! level ! fakesink silent=TRUE

This pipeline converts audio to 8-bit. The level element shows that the output levels still match the one for a sine wave.

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gst-launch-1.0 -v -m uridecodebin uri=file:///path/to/audio.flac ! audioconvert ! vorbisenc ! oggmux ! filesink location=audio.ogg

The vorbis encoder takes float audio data instead of the integer data output by most other audio elements. This pipeline decodes a FLAC audio file (or any other audio file for which decoders are installed) and re-encodes it into an Ogg/Vorbis audio file.

A mix matrix can be passed to audioconvert, that will govern the remapping of input to output channels.

Example matrix generation code

To generate the matrix using code:

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GValue v = G_VALUE_INIT;
GValue v2 = G_VALUE_INIT;
GValue v3 = G_VALUE_INIT;

g_value_init (&v2, GST_TYPE_ARRAY);
g_value_init (&v3, G_TYPE_FLOAT);
g_value_set_float (&v3, 1);
gst_value_array_append_value (&v2, &v3);
g_value_unset (&v3);
[ Repeat for as many float as your input channels - unset and reinit v3 ]
g_value_init (&v, GST_TYPE_ARRAY);
gst_value_array_append_value (&v, &v2);
g_value_unset (&v2);
[ Repeat for as many v2's as your output channels - unset and reinit v2]
g_object_set_property (G_OBJECT (audioconvert), "mix-matrix", &v);
g_value_unset (&v);

Example launch line

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gst-launch-1.0 audiotestsrc ! audio/x-raw, channels=4 ! audioconvert mix-matrix="<<(float)1.0, (float)0.0, (float)0.0, (float)0.0>, <(float)0.0, (float)1.0, (float)0.0, (float)0.0>>" ! audio/x-raw,channels=2 ! autoaudiosink

Example empty matrix generation code

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GValue v = G_VALUE_INIT;

g_value_init (&v, GST_TYPE_ARRAY);
g_object_set_property (G_OBJECT (audioconvert), "mix-matrix", &v);
g_value_unset (&v);

Example empty matrix launch line

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gst-launch-1.0 -v audiotestsrc ! audio/x-raw,channels=8 ! audioconvert mix-matrix="<>" ! audio/x-raw,channels=16,channel-mask=\(bitmask\)0x0000000000000000 ! fakesink

struct GstAudioConvert

struct GstAudioConvert;

The audioconvert object structure.

The “dithering” property

  “dithering”                GstAudioDitherMethod

Selects between different dithering methods.

Flags: Read / Write

Default value: GST_AUDIO_DITHER_TPDF

The “noise-shaping” property

  “noise-shaping”            GstAudioNoiseShapingMethod

Selects between different noise shaping methods.

Flags: Read / Write

Default value: GST_AUDIO_NOISE_SHAPING_NONE

The “mix-matrix” property

  “mix-matrix”               GstValueArray

Transformation matrix for input/output channels.

Flags: Read / Write