3 Copyright (C) 2004-2009 Ushodaya Enterprised Limited
4 Author: Charles Yates <charles.yates@pandora.be>
5 Author: Dan Dennedy <dan@dennedy.org>
6 Last Revision: 2011-04-03
14 Melt was developed as a test tool for the MLT framework. It can be thought
15 of as a powerful, if somewhat obscure, multitrack command line oriented
18 The following details the usage of the tool and as a result, provides a lot
19 of insight into the workings of the MLT framework.
24 melt [options] [producer [name=value]* ]+
26 -attach filter[:arg] [name=value]* Attach a filter to the output
27 -attach-cut filter[:arg] [name=value]* Attach a filter to a cut
28 -attach-track filter[:arg] [name=value]* Attach a filter to a track
29 -attach-clip filter[:arg] [name=value]* Attach a filter to a producer
30 -audio-track | -hide-video Add an audio-only track
31 -blank frames Add blank silence to a track
32 -consumer id[:arg] [name=value]* Set the consumer (sink)
33 -debug Set the logging level to debug
34 -filter filter[:arg] [name=value]* Add a filter to the current track
35 -group [name=value]* Apply properties repeatedly
36 -help Show this message
37 -join clips Join multiple clips into one cut
38 -mix length Add a mix between the last two cuts
39 -mixer transition Add a transition to the mix
40 -null-track | -hide-track Add a hidden track
41 -profile name Set the processing settings
42 -progress Display progress along with the position
43 -remove Remove the most recent cut
44 -repeat times Repeat the last cut
45 -query List all of the registered services
46 -query "consumers" | "consumer"=id List consumers or show info about one
47 -query "filters" | "filter"=id List filters or show info about one
48 -query "producers" | "producer"=id List producers or show info about one
49 -query "transitions" | "transition"=id List transitions or show info about one
50 -query "profile" | "profile"=id List profiles or show info about one
51 -serialise [filename] Write the commands to a text file
52 -silent Do not display position/transport help
53 -split relative-frame Split the last cut into two cuts
54 -swap Rearrange the last two cuts
56 -transition id[:arg] [name=value]* Add a transition
57 -verbose Set the logging level to verbose
58 -version Show the version and copyright message
59 -video-track | -hide-audio Add a video-only track
64 1. Order is incredibly important;
66 2. Error checking on command line parsing is weak;
68 3. Please refer to services.txt for details on services available;
70 4. The MLT framework, from which melt has inherited its naming convention,
71 is very mlt-centric. Producers produce MLT frame objects and consumers
72 consume MLT frame objects. The distinction is important - a DV producer
73 does not produce DV, it produces MLT frames from a DV source, and similarly
74 a DV consumer does not consume DV, it consumes MLT frames and produces DV
80 'Producers' typically refer to files but may also indicate devices (such as
81 dv1394 input or video4linux). Hence, the more generic term is used [the more
82 generic usage is out of scope for now...].
84 'Filters' are frame modifiers - they always guarantee that for every frame
85 they receive, they output *precisely* one frame. Never more, never less,
86 ever. Nothing says that a filter cannot generate frames though
88 'Transitions' collect frames from two tracks (a and b) and output 1
89 modified frame on their 'a track', and 1 unmodified frame on their 'b track'.
90 Never more, never less, ever.
92 'Consumers' collect frames from a producer, do something with them and
95 Collectively, these are known as 'services'.
97 All services have 'properties' associated to them. These are typically
98 defaulted or evaluated and may be overriden on a case by case basis.
100 All services except consumers obey in and out properties.
102 Consumers have no say in the flow of frames [though they may give the
103 illusion that they do]. They get frames from a connected producer, use them,
104 destroy them and get more.
109 To play a file with the default SDL PAL consumer, usage is:
113 Note that 'file' can be anything that melt has a known 'producer' mapping
114 for (so this can be anything from .dv to .txt).
116 You can also specify the producer directly, for example:
118 $ melt avformat:file.mpeg
120 Would force the direct use of avformat for loading the file.
125 Properties can be assigned to the producer by adding additional name=value
126 pairs after the producer:
128 $ melt file in=50 out=100 something="something else"
130 Note that while some properties have meaning to all producers (for example:
131 in, out and length are guaranteed to be valid for all, though typically,
132 length is determined automatically), the validity of others are dependent on
133 the producer - however, properties will always be assigned and silently
134 ignored if they won't be used.
139 Multiple files of different types can be used:
141 $ melt a.dv b.mpg c.png
143 Properties can be assigned to each file:
145 $ melt a.dv in=50 out=100 b.mpg out=500 c.png out=500
147 MLT will take care of 'normalising' the output of a producer to ensure
148 that the consumer gets what it needs. So, in the case above, the mlt
149 framework will ensure that images are rescaled and audio resampled to meet
150 the requirements of your configuration (which, by default, will be PAL).
151 See 'Appendix A: Normalisation Rules' below.
156 Filters are frame modifiers - they can change the contents of the audio or
157 the images associated to a frame.
159 $ melt a.dv -filter greyscale
161 As with producers, properties may be specified on filters too.
163 Again, in and out properties are common to all, so to apply a filter to a
164 range of frames, you would use something like:
166 $ melt a.dv -filter greyscale in=0 out=50
168 Again, filters have their own set of rules about properties and will
169 silently ignore properties that do not apply.
174 The -group switch is provided to force default properties on the following
175 'services'. For example:
177 $ melt -group in=0 out=49 clip*
179 would play the first 50 frames of all clips that match the wild card
182 Note that the last -group settings also apply to the following filters,
183 transitions and consumers, so:
185 $ melt -group in=0 out=49 clip* -filter greyscale
187 is *probably not* what you want (ie: the greyscale filter would only be
188 applied to the first 50 frames).
190 To shed the group properties, you can use any empty group:
192 $ melt -group in=0 out=49 clip* -group -filter greyscale
197 As described above, the -filter switch applies filters to an entire track. To
198 localise filters to a specific clip on a track, you have to know information
199 about the lengths of the clip and all clips leading up to it. In practise,
200 this is horrifically impractical, especially at a command line level (and not
201 even that practical from a programing point of view...).
203 The -attach family of switches simplify things enormously. By default, -attach
204 will attach a filter to the last service created, so:
206 $ melt clip1.dv clip2.dv -attach greyscale clip3.dv
208 would only apply the filter to clip2.dv. You can further narrow down the area of
209 the effect by specifying in/out points on the attached filter.
211 This might seem simple so far, but there is a catch... consider the following:
213 $ melt clip1.dv -attach watermark:+hello.txt -attach invert
215 The second attached filter is actually attached to the watermark. You might
216 think, yay, nice (and it is :-)), but, it might not be what you want. For example
217 you might want to attach both to clip1.dv. To do that, you can use:
219 $ melt clip1.dv -attach-cut watermark:+hello.txt -attach-cut invert
221 As you shall see below, there are still another couple of gotchas associated to
222 -attach, and even another variant :-).
227 The -mix switch provides the simplest means to introduce transitions between
232 $ melt clip1.dv clip2.dv -mix 25 -mixer luma -mixer mix:-1
234 would provide both an audio and video transition between clip1 and clip2.
236 This functionality supercedes the enforced use of the -track and -transition
237 switches from earlier versions of melt and makes life a lot easier :-).
239 These can be used in combination, so you can for example do a fade from black
240 and to black using the following:
242 $ melt colour:black out=24 clip1.dv -mix 25 -mixer luma \
243 colour:black out=24 -mix 25 -mixer luma
245 while this may not be immediately obvious, consider what's happening as the
246 command line is being parsed from left to right:
249 ----------------------- -----------------------------------------------------
250 colour:black out=24 [black]
251 clip1.dv [black][clip1.dv]
252 -mix 25 [black+clip1.dv][clip1.dv]
253 -mixer luma [luma:black+clip1.dv][clip1.dv]
254 colour:black out=24 [luma:black+clip1.dv][clip1.dv][black]
255 -mix 25 [luma:black+clip1.dv][clip1.dv][clip1.dv+black]
256 -mixer luma [luma:black+clip1.dv][clip1.dv][luma:clip1.dv+black]
258 Obviously, the clip1.dv instances refer to different parts of the clip, but
259 hopefully that will demonstrate what happens as we construct the track.
261 You will find more details on the mix in the framework.txt.
266 As noted, -attach normally applies to the last created service - so, you can
267 attach a filter to the transition region using:
269 $ melt clip1.dv clip2.dv -mix 25 -mixer luma -attach watermark:+Transition.txt
271 Again, nice, but take care - if you want the attached filter to be associated
272 to the region following the transition, use -attach-cut instead.
275 Splits, Joins, Removes and Swaps:
277 COMPLEX - needs simplification....
280 Introducing Tracks and Blanks:
282 So far, all of the examples have shown the definition of a single
283 playlist, or more accurately, track.
285 When multiple tracks exist, the consumer will receive a frame
286 from the 'highest numbered' track that is generating a non-blank
289 It is best to visualise a track arrangement, so we'll start with
292 $ melt a.dv -track b.dv in=0 out=49
294 This can be visualised as follows:
302 Playout will show the first 50 frames of b and the 51st frame shown will be
305 This rule also applies to audio only producers on the second track, for
306 example, the following would show the video from the a track, but the audio
307 would come from the second track:
309 $ melt a.dv -track b.mp3 in=0 out=49
311 To have the 51st frame be the first frame of b, we can use the -blank switch:
313 $ melt a.dv out=49 -track -blank 49 b.dv
315 Which we can visualise as:
319 +-------+-------------------+
321 +-------------------+
323 Now playout will continue as though a and b clips are on the
324 same track (which on its own, is about as useful as reversing the
325 process of slicing bread).
330 Where tracks become useful is in the placing of transitions.
332 Here we need tracks to overlap, so a useful multitrack
333 definition could be given as:
338 -transition luma in=25 out=49 a_track=0 b_track=1
340 Now we're cooking - our visualisation would be something like:
344 +---+---+--------------+
348 Playout will now show the first 25 frames of a and then a fade
349 transition for 25 frames between a and b, and will finally
350 playout the remainder of b.
353 Reversing a Transition:
355 When we visualise a track definition, we also see situations
358 +-------+ +----------+
360 +---+---+--------------+----+-----+
362 +-----------------------+
364 In this case, we have two transitions, a1 to b and b to a2.
366 In this scenario, we define a command line as follows:
368 $ melt a.dv out=49 -blank 49 a2.dv \
370 -blank 24 b.dv out=99 \
371 -transition luma in=25 out=49 a_track=0 b_track=1 \
372 -transition luma in=100 out=124 reverse=1 a_track=0 b_track=1
377 Melt has a built in serialisation mechanism - you can build up
378 your command, test it via any consumer and then add a -serialise
379 file.melt switch to save it.
381 The saved file can be subsequently used as a clip by melt or other
382 MLT applications. Take care though - paths to files are saved as
383 provided on the command line....
385 A more expressive serialisation can be obtained with the xml consumer
386 - this will provide an xml document which can be used freely in melt and
387 other MLT applications.
389 See mlt-xml.txt for more information.
394 Some filters/transitions should be applied on the output frame regardless
395 of which track it comes from - for example, you might have a 3rd text
396 track or a watermark which you want composited on every frame, and of
397 course, there's the obscure filter....
399 melt only supports this in two invocations - as a simple example:
401 $ melt a.dv -track -blank 100 b.dv -consumer xml:basic.mlt
402 $ melt basic.mlt -filter watermark:watermark.png