GStreamer1.0

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Port your Python app to PyGI, Gtk3, and GStreamer 1.0!

GStreamer 1.0 packages are now available in Ubuntu Quantal. For Ubuntu Precise (12.04 LTS) users, there are back-ported packages available in the GStreamer developers PPA. GnonLin and GES packages are not yet available for GStreamer 1.0 (but hopefully soon).

Although GStreamer 1.0 is not backward compatible with the GStreamer 0.10 series, it is parallel-installable. So you can safely install GStreamer 1.0 without effect on the many applications using GStreamer 0.10.

The focus here is porting Python apps. Also see:

Adding PPA for Ubuntu Precise

To use the back-ported packages for Ubuntu 12.04 LTS, add the GStreamer developers PPA like this:

  • sudo apt-add-repository ppa:gstreamer-developers/ppa
    sudo apt-get update

Installing GStreamer 1.0 packages

This should give you all the packages you likely want:

  • sudo apt-get install python-gi python3-gi \
        gstreamer1.0-tools \
        gir1.2-gstreamer-1.0 \
        gir1.2-gst-plugins-base-1.0 \
        gstreamer1.0-plugins-good \
        gstreamer1.0-plugins-ugly \
        gstreamer1.0-plugins-bad \
        gstreamer1.0-libav

Using GStreamer 1.0 from Python

You can use GStreamer 1.0 from Python (2 or 3) using PyGI like this:

  • >>> import gi
    >>> gi.require_version('Gst', '1.0')
    >>> from gi.repository import Gst
    >>> Gst.version()
    (1, 0, 0, 0)

Although currently the default will be Gst 1.0 if available, it's still a good idea to gi.require_version('Gst', '1.0') so that the code will clearly fail if Gst 1.0 isn't available.

The biggest change for Python users will be using the introspected API rather than the static python-gst bindings. However, there are also API changes in GStreamer itself, although these changes are generally more subtle.

Python Porting Guide

This is a guide to porting your PyGST app to GStreamer1.0 + PyGI.

To whet your appetite, here's a simple (less than 100 lines) PyGST video player, and here's the PyGI + GStreamer1.0 + Gtk3 port of that same simple video player.

Also see porting-to-1.0.txt. Although from a C perspective, you can usually figure out the equivalent Python API fairly easily once you get the hang of PyGI. Some obscure features might still be broken or unavailable through PyGI, so if you end up digging into the C code, you'll want to read about how the introspection annotations work.

Note that although you can sort-of use GStreamer0.10 with PyGI, key functionality is fundamentally broken and wont ever be fixed in GStreamer0.10 (because it would require API breakage). It's unproductive to try and first port to PyGI, then to GStreamer1.0. You should do both in one move.

If your PyGST app is also a PyGTK app (fairly likely), you must port the Gtk bits to PyGI + Gtk3 at the same time. You cannot use PyGI and any of the static python-gobject based bindings together in the same process.

You just have to jump into the deep end and go for it! If you have extensive unit tests, pat yourself on the back, because you'll have a much easier time.

On the upside, once you port to PyGI, it's generally very easy to port to Python3. And you should, all the cool kids are doing it.

Examples

Some small reference examples of common GStreamer use-cases, with both a 0.10 and a 1.0 version:

Video Player:

video-player-0.10

video-player-1.0

Webcam Capture:

webcam-0.10

webcam-1.0

A/V Transcoder:

transcoder-0.10

transcoder-1.0

Python Element:

plugin-0.10

plugin-1.0

Grab all the example code and the sample video like this:

  • bzr branch lp:~jderose/+junk/gst-examples

debian/control

You'll have to update your debian/control, of course. So replace something like this:

  • Depends: python-gst0.10,
        gstreamer0.10-plugins-good,
        gstreamer0.10-plugins-ugly,
        gstreamer0.10-plugins-bad,
        gstreamer0.10-ffmpeg

With this:

  • Depends: python-gi,
        gir1.2-gstreamer-1.0,
        gir1.2-gst-plugins-base-1.0,
        gstreamer1.0-plugins-good,
        gstreamer1.0-plugins-ugly,
        gstreamer1.0-plugins-bad,
        gstreamer1.0-libav

Then when you port to Python3, replace python-gi with python3-gi.

Imports

Replace:

  • import gobject
    import gst

With:

  • import gi
    gi.require_version('Gst', '1.0')
    from gi.repository import GObject, Gst

After that a bit of search and replace (used with care) can help. Basically:

  • gobject.* => GObject.*
    gst.* => Gst.*

Gst.init()

You should call GObject.threads_init() in your module-scope, right after your imports. Unlike the static bindings, you also need to call Gst.init(). So replace:

  • gobject.threads_init()

With:

  • GObject.threads_init()
    Gst.init(None)

element_factory_make()

Replace:

  • src = gst.element_factory_make('filesrc')

With:

  • src = Gst.ElementFactory.make('filesrc', None)

Note that unlike element_factory_make(), ElementFactory.make() will return None rather than raising an exception when the element is not found.

There is no equivalent to gst.element_link_many(), so replace:

  • gst.element_link_many(one, two, three)

With:

  • one.link(two)
    two.link(three)

Pipeline.add(one, two)

Bin.add() can't be overloaded to add multiple elements at once, so replace:

  • pipeline = gst.Pipeline()
    pipeline.add(one, two)

With:

  • pipeline = Gst.Pipeline()
    pipeline.add(one)
    pipeline.add(two)

one.link(two, mycaps)

Replace:

  • one.link(two, mycaps)

With:

  • one.link_filtered(two, mycaps)

STATE_PLAYING

Replace:

  • pipeline.set_state(gst.STATE_PLAYING)

With:

  • pipeline.set_state(Gst.State.PLAYING)

And so on. Some search-and-replace is helpful here, basically:

  • gst.STATE_* => Gst.State.*

SEEK_FLAG_FLUSH

Replace something like this:

  • pipeline.seek_simple(
        gst.FORMAT_TIME,
        gst.SEEK_FLAG_FLUSH | gst.SEEK_FLAG_KEY_UNIT,
        nanoseconds
    )

With this:

  • pipeline.seek_simple(
        Gst.Format.TIME,
        Gst.SeekFlags.FLUSH | Gst.SeekFlags.KEY_UNIT,
        nanoseconds
    )

Search and replace:

  • gst.SEEK_FLAG_* => Gst.SeekFlags.*

FORMAT_TIME

Search and replace:

  • gst.FORMAT_* => Gst.Format.*

prepare-xwindow-id

"prepare-xwindow-id" has been renamed "prepare-window-handle", and a few other details have changed (some on the PyGI + Gtk3 side).

So replace something like this:

  • xid = drawingarea.window.xid
    
    def on_sync_message(bus, msg):
        if msg.structure.get_name() == 'prepare-xwindow-id':
            msg.src.set_xwindow_id(xid)

With this:

  • xid = drawingarea.get_property('window').get_xid()
    
    def on_sync_message(bus, msg):
        if msg.get_structure().get_name() == 'prepare-window-handle':
            msg.src.set_window_handle(xid)

Note that trying to get the drawingarea XID in your on_sync_message() handler will cause a segfault because of threading issues.

Also note that for the above to work, you must have imported both GdkX11 and GstVideo. So in your imports, make sure to include something like this:

  • # Needed for window.get_xid(), xvimagesink.set_window_handle(), respectively:
    from gi.repository import GdkX11, GstVideo

See this video-player-1.0 script for a simple video player example. You might want to compare it to video-player-0.10 to see how the same thing was done with python-gst.

GhostPad

You've got to use GhostPad.new(). So replace:

  • ghost = gst.GhostPad('sink', mysinkpad)

With:

  • ghost = Gst.GhostPad.new('sink', mysinkpad)

Pad.get_caps()

In callbacks for "pad-added" events and similar, it's common to use the string representation of the pad caps as a way to decide whether to link a pad and what to link the pad to.

You need to use Pad.query_caps() instead of Pad.get_caps(), and the returned object is no longer array-like. So in general replace this pattern:

  • def on_pad_added(element, pad):
        string = pad.get_caps()[0].get_name()
        if string.startswith('audio/'):
            <link to some audio elements>

With this:

  • def on_pad_added(element, pad):
        string = pad.query_caps(None).to_string()
        if string.startswith('audio/'):
            <link to some audio elements>

Element.get_pad()

Element.get_pad() has been renamed Element.get_static_pad(). So replace something like this:

  • src = gst.element_factory_make('filesink')
    pad = src.get_pad('sink')

With this:

  • src = Gst.ElementFactory.make('filesink', None)
    pad = src.get_static_pad('sink')

Buffer.data

In a "preroll-handoff" or "handoff" callback, it's common to want access to the buffer data. A common use case is saving a JPEG thumbnail to a file, for example.

Replace something like this:

  • def on_preroll_handoff(element, buf, pad):
        data = buf.data

With this:

  • def on_preroll_handoff(element, buf, pad):
        data = buf.extract_dup(0, buf.get_size())

Buffer.timestamp

Buffer.timestamp has been renamed to Buffer.pts (Presentation Time Stamp). So replace something like this:

  • def on_handoff(element, buf, pad):
        timestamp = buf.timestamp

With this:

  • def on_handoff(element, buf, pad):
        timestamp = buf.pts

There is also the new Buffer.dts (Decode Time Stamp). Often pts and dts will be the same, but B-frames are an example of when they'll be different.

Pad.get_negotiated_caps()

Pad.get_negotiated_caps() has been renamed Pad.get_current_caps(), so replace:

  • caps = pad.get_negotiated_caps()

With:

  • caps = pad.get_current_caps()

caps[0]

Caps objects are not array-like from PyGI, so replace:

  • cap = caps[0]

With:

  • cap = caps.get_structure(0)

caps[0]['foo']

Individual capability structures are not dictionary-like objects from PyGI, so you need to use type-appropriate accessor methods instead. For example, replace this:

  • framerate = caps[0]['framerate']
    width = caps[0]['width']
    height = caps[0]['height']

With:

  • (success, num, denom) = caps.get_structure(0).get_fraction('framerate')
    (success, width) = caps.get_structure(0).get_int('width')
    (success, height) = caps.get_structure(0).get_int('height')

query_new_duration()

Replace:

  • query = gst.query_new_duration(Gst.FORMAT_TIME)

With:

  • query = Gst.Query.new_duration(Gst.Format.TIME)

audio/x-raw, video/x-raw

"audio/x-raw-int" and "audio/x-raw-float" have been condensed into a unified "audio/x-raw" with a flexible format description.

Likewise, "video/x-raw-yuv" and "video/x-raw-rgb" have been condensed into a unified "video/x-raw" with a flexible format description.

This is much nicer because in GStreamer 0.10 certain element details were leaked that really shouldn't have been. For example, if you wanted filter caps to force a certain sample-rate, you previously needed to know whether, say, an audio encoder took audio/x-raw-int or audio/x-raw-float.

So now you can replace say:

  • caps = gst.caps_from_string('audio/x-raw-float, rate=(int)44100')

With:

  • caps = Gst.caps_from_string('audio/x-raw, rate=(int)44100')

As you're only interested in specifying the rate anyway, it's much nicer to be truly abstracted from the format details.

element_register()

The gst.element_register() function had some magic to create an in-process plugin on the fly if needed (assuming Jason understood this detail correctly when talking with Edward Hervey about it).

You can still register in-process elements with PyGI, but you need to use a bit more of the C API now and explicitly register your plugin, and then register your elements. So replace something like this:

  • gobject.type_register(DmediaSrc)
    gst.element_register(DmediaSrc, 'dmediasrc')

With something like this:

  • def plugin_init(plugin, userarg):
        DmediaSrcType = GObject.type_register(DmediaSrc)
        Gst.Element.register(plugin, 'dmediasrc', 0, DmediaSrcType)
        return True
    
    version = Gst.version()
    Gst.Plugin.register_static_full(
        version[0],  # GST_VERSION_MAJOR
        version[1],  # GST_VERSION_MINOR
        'dmedia',
        'dmedia src plugin',
        plugin_init,
        '12.06',
        'LGPL',
        'dmedia',
        'dmedia',
        'https://launchpad.net/dmedia',
        None,
    )

See plugin-0.10 for an example python-gst plugin, and then plugin-1.0 for how to do the same with PyGI and GSTreamer 1.0.

PAD_SRC, PAD_ALWAYS

Search and replace:

  • gst.PAD_SRC => Gst.PadDirection.SRC
    gst.PAD_SINK => Gst.PadDirection.SINK
    gst.PAD_ALWAYS => Gst.PadPresence.ALWAYS
    gst.PAD_REQUEST => Gst.PadPresence.REQUEST
    gst.PAD_SOMETIMES => Gst.PadPresence.SOMETIMES

URIHandler

With PyGST, you can do something like this to implement the GstUriHandler interface in a custom element:

  • class DmediaSrc(gst.Bin, gst.URIHandler):
        @classmethod
        def do_get_type_full(cls):
            return gst.URI_SRC
    
        @classmethod
        def do_get_protocols_full(cls):
            return ['dmedia']
    
        def do_set_uri(self, uri):
            if not uri.startswith('dmedia://'):
                return False
            self.uri = uri
            return True
    
        def do_get_uri(self):
            return self.uri

(Note many details were left out above, see plugin-0.10 for the full working example.)

Currently it seems this isn't possible with PyGI + GStreamer 1.0. See bug 679181.

decodebin2

The "decodebin2" element has been renamed to "decodebin", and the old "decodebin" element has been removed.

playbin2

The "playbin2" element has been renamed to "playbin", and the old "playbin" element has been removed.

ffmpegcolorspace

The "ffmpegcolorspace" element has been replaced with the new "videoconvert" element.

ffmpeg => libav

All the major distros now ship the libav fork of ffmpeg (and current GStreamer 0.10 packages build against libav, not ffmpeg). GStreamer 1.0 was an opportunity to do some renaming to reflect this change.

gstreamer1.0-libav is the equivalent of the the gstreamer0.10-ffmpeg Debian package.

Additionally, the GStreamer elements have been renamed. For example, in 1.0 use avdec_h264 instead of ffdec_h264. Basically some search and replace:

  • ffvideoscale => avvideoscale
    ffdec_* => avdec_*
    ffenc_* => avenc_*
    ffmux_* => avmux_*
    ffdemux_* => avdemux_*

To see all the elements shipped in the gstreamer1.0-libav package, run:

  • gst-inspect-1.0 libav

The equivalent command for gstreamer0.10-ffmpeg is:

  • gst-inspect-0.10 ffmpeg

gnlfilesource

The "gnlfilesource" element has been removed, so now use the "gnlurisource" element instead.

Replace:

  • src = gst.element_factory_make('gnlfilesource')
    src.set_property('location', '/my/cool/video')

With:

  • src = Gst.ElementFactory.make('gnlurisource')
    src.set_property('uri', 'file:///my/cool/video')

Novacut/GStreamer1.0 (last edited 2014-03-14 20:16:15 by jderose)