Gstreamer-editing-services used to make a fancy mixing script.

mixit.py

from gi.repository import GstPbutils
from gi.repository import Gtk
from gi.repository import Gst
from gi.repository import GES
from gi.repository import GObject

import sys
import signal

def handle_sigint(sig, frame):
    Gtk.main_quit()

def busMessageCb(unused_bus, message):
    if message.type == Gst.MessageType.EOS:
        print "eos"
        Gtk.main_quit()

def duration_querier(pipeline):
    print pipeline.query_position(Gst.Format.TIME)
    return True

def mylog(x):
    return (x / (1 + x))

def createLayers(timeline, asset):
    step = 1.0 / int(sys.argv[2])
    alpha = step
    for i in range(int(sys.argv[2])):
        layer = timeline.append_layer()
        clip = layer.add_asset(asset, i * Gst.SECOND * 0.3, 0, asset.get_duration(), GES.TrackType.UNKNOWN)
        for source in clip.get_children(False):
            if source.props.track_type == GES.TrackType.VIDEO:
                break

        source.set_child_property("alpha", alpha)
        alpha += step

if __name__ =="__main__":
    if len(sys.argv) < 4:
        print "usage : " + sys.argv[0] + " file:///video/uri number_of_layers file:///audio/uri [file:///output_uri]"
        print "If you specify a output uri, the pipeline will get rendered"
        exit(0)

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

    timeline = GES.Timeline.new_audio_video()

    asset = GES.UriClipAsset.request_sync(sys.argv[1])
    audio_asset = GES.UriClipAsset.request_sync(sys.argv[3])

    createLayers(timeline, asset)

    timeline.commit()

    layer = timeline.append_layer()

    layer.add_asset(audio_asset, 0, 0, timeline.get_duration(), GES.TrackType.AUDIO)

    pipeline = GES.Pipeline()
    pipeline.set_timeline(timeline)

    container_profile = \
        GstPbutils.EncodingContainerProfile.new("pitivi-profile",
                                                "Pitivi encoding profile",
                                                Gst.Caps("video/webm"),
                                                None)

    video_profile = GstPbutils.EncodingVideoProfile.new(Gst.Caps("video/x-vp8"),
                                                        None,
                                                        Gst.Caps("video/x-raw"),
                                                        0)

    container_profile.add_profile(video_profile)

    audio_profile = GstPbutils.EncodingAudioProfile.new(Gst.Caps("audio/x-vorbis"),
                                                        None,
                                                        Gst.Caps("audio/x-raw"),
                                                        0)

    container_profile.add_profile(audio_profile)

    if len(sys.argv) > 4:
        pipeline.set_render_settings(sys.argv[4], container_profile)
        pipeline.set_mode(GES.PipelineFlags.RENDER)

    pipeline.set_state(Gst.State.PLAYING)

    bus = pipeline.get_bus()
    bus.add_signal_watch()
    bus.connect("message", busMessageCb)
    GObject.timeout_add(300, duration_querier, pipeline)

    signal.signal(signal.SIGINT, handle_sigint)
    Gtk.main()