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108 lines
3.2 KiB
Markdown
108 lines
3.2 KiB
Markdown
# QtGStreamer vs C GStreamer
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QtGStreamer is designed to mirror the C GStreamer API as closely as
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possible. There are, of course, minor differences. They are documented
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here.
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# Common Functions
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<table>
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<colgroup>
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<col width="50%" />
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<col width="50%" />
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</colgroup>
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<thead>
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<tr class="header">
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<th>C GStreamer</th>
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<th>QtGStreamer</th>
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</tr>
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</thead>
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<tbody>
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<tr class="odd">
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<td><code>gst_element_factory_make()</code></td>
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<td><code>QGst::ElementFactory::make(const QString &factoryName, const char *elementName=NULL)</code></td>
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</tr>
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<tr class="even">
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<td><code>gst_parse_bin_from_description()</code></td>
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<td><code>QGst::Bin::fromDescription(const QString &description, BinFromDescriptionOption ghostUnlinkedPads=Ghost)</code></td>
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</tr>
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<tr class="odd">
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<td><code>gst_caps_from_string()</code></td>
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<td><p><code>QGst::Caps::fromString(const QString &string)</code></p></td>
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</tr>
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<tr class="even">
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<td><code>g_signal_connect()</code></td>
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<td><code>QGlib::connect(GObject* instance, const char *detailedSignal, T *receiver, R(T::*)(Args...) slot, ConnectFlags flags)</code></td>
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</tr>
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</tbody>
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</table>
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# Naming Convention
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QtGStreamer follows a strict naming policy to help make cross
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referencing easier:
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### Namespaces
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The "G" namespace (`GObject`, `GValue`, etc...) is referred to as
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"QGlib".
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The "Gst" namespace (`GstObject`, `GstElement`, etc...) is referred to
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as "QGst".
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### Class Names
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Class names should be the same as their G\* equivalents, with the
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namespace prefix removed. For example, "`GstObject`" becomes
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"`QGst::Object`", "`GParamSpec`" becomes "`QGlib::ParamSpec`", etc...
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### Method Names
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In general the method names should be the same as the GStreamer ones,
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with the g\[st\]\_\<class\> prefix removed and converted to camel case.
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For example,
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``` lang=c
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gboolean gst_caps_is_emtpy(const GstCaps *caps);
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```
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becomes:
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``` lang=c
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namespace QGst {
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class Caps {
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bool isEmpty() const;
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}
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}
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```
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There are cases where this may not be followed:
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1. **Properties**. Most property getters have a "get" prefix, for
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example, `gst_object_get_name()`. In QtGStreamer the "get" prefix is
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omitted, so this becomes just `name()`.
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2. **Overloaded members**. In C there is no possibility to have two
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methods with the same name, so overloaded members usually have some
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extra suffix, like "\_full". For example, `g_object_set_data()` and
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`g_object_set_data_full()`. In C++ we just add a method with the
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same name, or put optional parameters in the existing method.
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3. **Other cases where the glib/gstreamer method name doesn't make much
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sense**. For example, `gst_element_is_locked_state()`. That doesn't
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make sense in english, as "sate" is the subject and should go before
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the verb "is". So, it becomes `stateIsLocked()`.
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# Reference Counting
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Reference counting is handled the same way as Qt does. There is no need
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to call `g_object_ref()`` and g_object_unref()`.
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# Access to GStreamer Elements
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QtGStreamer provides access to the underlying C objects, in case you
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need them. This is accessible with a simple cast:
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``` lang=c
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ElementPtr qgstElement = QGst::ElementFactory::make("playbin2");
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GstElement* gstElement = GST_ELEMENT(qgstElement);
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```
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