3 Before running the demo script, make sure you '. setenv' from the parent
4 directory. Also, please create clips clip1.dv, clip2.dv, clip3.dv, clip1.mpeg,
5 clip2.mpeg, clip3.mpeg, and music1.ogg. Please make sure clips are at least 500
8 These notes explain the the concepts presented in each demonstration and
9 what details to look for.
11 First, a note on consumers. When you start the script, the main menu asks
12 you to choose a consumer. A consumer is like a viewer, but it could also
13 write to a stream/file. The "SDL" consumer is the popular Simple DirectMedia
14 Layer audio and video output. The "Westley" consumer generates an XML
15 representation of the service network. That can be played directly due to the
16 westley producer plugin. See docs/westley.txt for more information. The
17 "MainConcept DV" consumer refers to the proprietary MLT plugin required to
18 use MLT with MainConcept DV, DVCPro, and MPEG codecs. "/dev/dv1394/0" refers
19 to a device file for transmitting DV over FireWire using the Linux dv1394 kernel
20 module. The "BlueFish444" consumer is another proprietary plugin to use
21 the BlueFish444 manufactured SDI video/audio output cards with MLT.
27 Simply builds a playlist containing each video clip, and you can transport
28 between them using j and k keys.
32 A video filter can be applied to a portion of a producer (clip, playlist,
33 or multitrack). This examples shows the greyscale filter.
37 A graphic can overlay video in realtime with support for alpha channel.
38 This example uses a PNG file with an alpha channel. Distortion is explicitly
39 enabled here so the otherwise circular graphic is scaled to fill the
40 compositing region. By default, compositing honours the aspect ratio of the
45 Titles are very easy to composite in realtime. The titler uses Pango
46 with the FreeType2 rendering backend. This means it supports high
47 quality scalable font rendering with anti-aliasing, unicode (UTF-8),
48 and Pango markup capabilities. The compsiting here respects the aspect
49 ratio of the rendered title in the first two title pieces but distorts
50 the final one. This demo also shows the motion and scaling capabilities
51 of the compositor in conjunction with honouring aspect. The compositor
52 is doing field-based rendering. So, when displayed non-progressively
53 with SDL, you can see motion artifacts during animation.
55 A composite transition
57 The compositor also handles video over video as demonstrated in this
58 usage of the compositor to create a special transition. This demonstration
59 also crossfades the audio during the transition! Progressive rendering
60 is explicitly enabled on the compositor due to the poor results that
61 would otherwise occur due to scaling an interleaved video frame and moving
62 the video in a reverse direction horizontally.
66 A simple series of transitions betwen 3 clips using dissolves and audio
67 crossfades. This is easy :-).
71 Wipe transitions are very easy and highly extensible as they are generated
72 using a very convenient lookup table based upon the luma of an image.
73 This image can be a 16 bit PGM (grayscale bitmap) or the luma channel of
74 any video producer. A number of high quality wipes can be downloaded from
75 http://mlt.sf.net/. It also performs field rendering.
76 The second wipe demonstrates the ability to control the direction of the
81 A popular requirement in news production is to obscure a face, obscenity,
82 or trademarked logo. This demonstrates using a simple rectangular
83 obscure filter applied to a region of the image. The second example is more
84 advanced and shows using the "region" filter to select the image area and a
85 property of the region filter to "shape" the region using the alpha channel
86 of another image (circle.png) and another property to "filter" the region
87 using the obscure filter.
91 A music bed sound track can be mixed with a video. The sound track of the
92 video clip has a "floating" amplitude normalisation filter applied.
93 Typically, audio normalisation applies a constant gain factor across the
94 entire duration of an audio segment from a single source where the
95 gain factor is automatically determined by anaylsing the maximum "power"
96 or peak levels. However, in news production, a popular requirement is to
97 to dynamically boost the amplitude in soft areas and reduce the amplitude
98 in louder areas. Thus, the gain analysis is performed using a "sliding
99 window" approach. This example also applies a constant gain factor of
100 0.5 (50%) to the normalised audio of the video clip (to get a nicer
103 Audio and Video Levels
105 Audio can be normalised by setting a target amplitude level in decibels.
106 A gamma curve can be applied to the luma channel of video.
108 Shadowed Title and Watermark
110 Two instances of the titler are used to create a shadow effect.
111 The aspect ratio of the watermark in this example is not distorted. Since
112 the original image is a circle with square pixels--a computer-generated
113 image--and ITU BT.601 video is not composed of square samples. Therefore,
114 the compositor normalises the pixel aspect ratio of the overlay to the
115 destination image, and the circular image remains circular on the analog
116 video output. Finally, a greyscale filter is applied to the watermark
117 while its opacity is set at 30%.
119 Station Promo into Story?
121 Here is fun demo that might show using a still graphic with some music
122 to introduce a show. A luma wipe with an audio crossfade transitions from
123 the show title or station promotional material.
125 Voiceover 2 clips with title
127 A common news production requirement to have a "voiceover" audio track
128 to a clip or even multiple clips as demonstrated here. Likewise, it is
129 common to place a title caption on the video at the same time! This
130 demo has a little fun with the titler at the sake of practicality :-)
131 The foreground of the title is transparent while the opacity of the
132 background is reduced to blend with the video. Meanwhile, the compositor
133 stretches the image to fill the bottom slice of the video--not suitable
134 for overscan displays ;-)
136 Also, pay close attention to the mixing levels of the audio tracks.
137 The audio of the video fades out as the voiceover track (just music
138 in this demo) fades in. Then, the voiceover remains mixed with the
139 ambient audio at a 60% level. Finally, the voiceover fades out smoothly
140 from the 60% level to nothing.
144 This demo requires a special TrueType font called Avantika. If you have the
145 font, register it with fontconfig using the fc-cache utility. This
146 demonstrates i18n capabilities of the titler and the alignment capabilities
147 of both the titler and the compositor. The titler centre aligns
148 the two lines of text, and the compositor centre aligns the title
149 horizontally on the frame.
153 You can superimpose a title over a graphic over video! Also,
154 you can apply a luma wipe to the compositor!
158 This demo requires any number of JPEG images with the extension ".jpg"
159 in a subdirectory named "Scotland."
163 The "watermark" filter encapsulates the compositor, and you have full
164 control over the compositor properties. Who says a watermark can not
169 A variation on the above Bouncy, Bouncy demo that applies a shape, or
170 alpha producer, to the the compositing region.
174 This demonstrates layout capabilities of the compositor.
178 This demonstrates a distorting barndoor-like wipe.
183 A J cut is an edit where the audio cuts before the video.
184 It gets its name from the way it looks on a NLE timeline user interface.
185 When the audio cuts over, it does an audio crossfade over the duration of
186 one frame. This makes the audio cut slightly less abrupt and avoids any
187 "click" due to mismatched sample levels at the edit point. The video edit
192 An L cut is an edit where the video cuts before the audio.
193 It gets its name from the way it looks on a NLE timeline user interface.
194 This demo shows a very quick dissolve over 5 frames for a soft video cut.
195 Like the J Cut demo, an audio crossfade for the duration of one frame makes
196 an audio edit nearly instantaneous while being slightly softened and
197 avoiding aberrations.
199 Fade from/to black/silence
201 Of course, it is possible using MLT to fade from black on video and silence
202 on audio as well fade to black and silence.
206 A push wipe is a somewhat fancier transition than most standard wipes
207 because it involves motion. The new video clip "pushes" the old video
208 clip off one edge. If you can preview on an analog monitor you will notice
209 how smooth the motion is due to field-based rendering.
213 A very minimal reverse crawling title neard the bottom of the screen.
214 The goal of the demo is show fluid motion of the field-based rendering of
215 the compositor when viewed on an analog monitor using a DV or BlueFish444
216 consumer. The demo also shows the potientional for using and extending the
217 existing set of services for a full blown news ticker implementation.
projects / melted / blob