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 "profiles" | "profile"=id List profiles or show info about one
51 -query "formats" List audio/video formats
52 -query "audio_codecs" List audio codecs
53 -query "video_codecs" List video codecs
54 -serialise [filename] Write the commands to a text file
55 -silent Do not display position/transport help
56 -split relative-frame Split the last cut into two cuts
57 -swap Rearrange the last two cuts
59 -transition id[:arg] [name=value]* Add a transition
60 -verbose Set the logging level to verbose
61 -version Show the version and copyright message
62 -video-track | -hide-audio Add a video-only track
67 1. Order is incredibly important;
69 2. Error checking on command line parsing is weak;
71 3. Please refer to services.txt for details on services available;
73 4. The MLT framework, from which melt has inherited its naming convention,
74 is very mlt-centric. Producers produce MLT frame objects and consumers
75 consume MLT frame objects. The distinction is important - a DV producer
76 does not produce DV, it produces MLT frames from a DV source, and similarly
77 a DV consumer does not consume DV, it consumes MLT frames and produces DV
83 'Producers' typically refer to files but may also indicate devices (such as
84 dv1394 input or video4linux). Hence, the more generic term is used [the more
85 generic usage is out of scope for now...].
87 'Filters' are frame modifiers - they always guarantee that for every frame
88 they receive, they output *precisely* one frame. Never more, never less,
89 ever. Nothing says that a filter cannot generate frames though
91 'Transitions' collect frames from two tracks (a and b) and output 1
92 modified frame on their 'a track', and 1 unmodified frame on their 'b track'.
93 Never more, never less, ever.
95 'Consumers' collect frames from a producer, do something with them and
98 Collectively, these are known as 'services'.
100 All services have 'properties' associated to them. These are typically
101 defaulted or evaluated and may be overriden on a case by case basis.
103 All services except consumers obey in and out properties.
105 Consumers have no say in the flow of frames [though they may give the
106 illusion that they do]. They get frames from a connected producer, use them,
107 destroy them and get more.
112 To play a file with the default SDL PAL consumer, usage is:
116 Note that 'file' can be anything that melt has a known 'producer' mapping
117 for (so this can be anything from .dv to .txt).
119 You can also specify the producer directly, for example:
121 $ melt avformat:file.mpeg
123 Would force the direct use of avformat for loading the file.
128 Properties can be assigned to the producer by adding additional name=value
129 pairs after the producer:
131 $ melt file in=50 out=100 something="something else"
133 Note that while some properties have meaning to all producers (for example:
134 in, out and length are guaranteed to be valid for all, though typically,
135 length is determined automatically), the validity of others are dependent on
136 the producer - however, properties will always be assigned and silently
137 ignored if they won't be used.
142 Multiple files of different types can be used:
144 $ melt a.dv b.mpg c.png
146 Properties can be assigned to each file:
148 $ melt a.dv in=50 out=100 b.mpg out=500 c.png out=500
150 MLT will take care of 'normalising' the output of a producer to ensure
151 that the consumer gets what it needs. So, in the case above, the mlt
152 framework will ensure that images are rescaled and audio resampled to meet
153 the requirements of your configuration (which, by default, will be PAL).
154 See 'Appendix A: Normalisation Rules' below.
159 Filters are frame modifiers - they can change the contents of the audio or
160 the images associated to a frame.
162 $ melt a.dv -filter greyscale
164 As with producers, properties may be specified on filters too.
166 Again, in and out properties are common to all, so to apply a filter to a
167 range of frames, you would use something like:
169 $ melt a.dv -filter greyscale in=0 out=50
171 Again, filters have their own set of rules about properties and will
172 silently ignore properties that do not apply.
177 The -group switch is provided to force default properties on the following
178 'services'. For example:
180 $ melt -group in=0 out=49 clip*
182 would play the first 50 frames of all clips that match the wild card
185 Note that the last -group settings also apply to the following filters,
186 transitions and consumers, so:
188 $ melt -group in=0 out=49 clip* -filter greyscale
190 is *probably not* what you want (ie: the greyscale filter would only be
191 applied to the first 50 frames).
193 To shed the group properties, you can use any empty group:
195 $ melt -group in=0 out=49 clip* -group -filter greyscale
200 As described above, the -filter switch applies filters to an entire track. To
201 localise filters to a specific clip on a track, you have to know information
202 about the lengths of the clip and all clips leading up to it. In practise,
203 this is horrifically impractical, especially at a command line level (and not
204 even that practical from a programing point of view...).
206 The -attach family of switches simplify things enormously. By default, -attach
207 will attach a filter to the last service created, so:
209 $ melt clip1.dv clip2.dv -attach greyscale clip3.dv
211 would only apply the filter to clip2.dv. You can further narrow down the area of
212 the effect by specifying in/out points on the attached filter.
214 This might seem simple so far, but there is a catch... consider the following:
216 $ melt clip1.dv -attach watermark:+hello.txt -attach invert
218 The second attached filter is actually attached to the watermark. You might
219 think, yay, nice (and it is :-)), but, it might not be what you want. For example
220 you might want to attach both to clip1.dv. To do that, you can use:
222 $ melt clip1.dv -attach-cut watermark:+hello.txt -attach-cut invert
224 As you shall see below, there are still another couple of gotchas associated to
225 -attach, and even another variant :-).
230 The -mix switch provides the simplest means to introduce transitions between
235 $ melt clip1.dv clip2.dv -mix 25 -mixer luma -mixer mix:-1
237 would provide both an audio and video transition between clip1 and clip2.
239 This functionality supercedes the enforced use of the -track and -transition
240 switches from earlier versions of melt and makes life a lot easier :-).
242 These can be used in combination, so you can for example do a fade from black
243 and to black using the following:
245 $ melt colour:black out=24 clip1.dv -mix 25 -mixer luma \
246 colour:black out=24 -mix 25 -mixer luma
248 while this may not be immediately obvious, consider what's happening as the
249 command line is being parsed from left to right:
252 ----------------------- -----------------------------------------------------
253 colour:black out=24 [black]
254 clip1.dv [black][clip1.dv]
255 -mix 25 [black+clip1.dv][clip1.dv]
256 -mixer luma [luma:black+clip1.dv][clip1.dv]
257 colour:black out=24 [luma:black+clip1.dv][clip1.dv][black]
258 -mix 25 [luma:black+clip1.dv][clip1.dv][clip1.dv+black]
259 -mixer luma [luma:black+clip1.dv][clip1.dv][luma:clip1.dv+black]
261 Obviously, the clip1.dv instances refer to different parts of the clip, but
262 hopefully that will demonstrate what happens as we construct the track.
264 You will find more details on the mix in the framework.txt.
269 As noted, -attach normally applies to the last created service - so, you can
270 attach a filter to the transition region using:
272 $ melt clip1.dv clip2.dv -mix 25 -mixer luma -attach watermark:+Transition.txt
274 Again, nice, but take care - if you want the attached filter to be associated
275 to the region following the transition, use -attach-cut instead.
278 Splits, Joins, Removes and Swaps:
280 COMPLEX - needs simplification....
283 Introducing Tracks and Blanks:
285 So far, all of the examples have shown the definition of a single
286 playlist, or more accurately, track.
288 When multiple tracks exist, the consumer will receive a frame
289 from the 'highest numbered' track that is generating a non-blank
292 It is best to visualise a track arrangement, so we'll start with
295 $ melt a.dv -track b.dv in=0 out=49
297 This can be visualised as follows:
305 Playout will show the first 50 frames of b and the 51st frame shown will be
308 This rule also applies to audio only producers on the second track, for
309 example, the following would show the video from the a track, but the audio
310 would come from the second track:
312 $ melt a.dv -track b.mp3 in=0 out=49
314 To have the 51st frame be the first frame of b, we can use the -blank switch:
316 $ melt a.dv out=49 -track -blank 49 b.dv
318 Which we can visualise as:
322 +-------+-------------------+
324 +-------------------+
326 Now playout will continue as though a and b clips are on the
327 same track (which on its own, is about as useful as reversing the
328 process of slicing bread).
333 Where tracks become useful is in the placing of transitions.
335 Here we need tracks to overlap, so a useful multitrack
336 definition could be given as:
341 -transition luma in=25 out=49 a_track=0 b_track=1
343 Now we're cooking - our visualisation would be something like:
347 +---+---+--------------+
351 Playout will now show the first 25 frames of a and then a fade
352 transition for 25 frames between a and b, and will finally
353 playout the remainder of b.
356 Reversing a Transition:
358 When we visualise a track definition, we also see situations
361 +-------+ +----------+
363 +---+---+--------------+----+-----+
365 +-----------------------+
367 In this case, we have two transitions, a1 to b and b to a2.
369 In this scenario, we define a command line as follows:
371 $ melt a.dv out=49 -blank 49 a2.dv \
373 -blank 24 b.dv out=99 \
374 -transition luma in=25 out=49 a_track=0 b_track=1 \
375 -transition luma in=100 out=124 reverse=1 a_track=0 b_track=1
380 Melt has a built in serialisation mechanism - you can build up
381 your command, test it via any consumer and then add a -serialise
382 file.melt switch to save it.
384 The saved file can be subsequently used as a clip by melt or other
385 MLT applications. Take care though - paths to files are saved as
386 provided on the command line....
388 A more expressive serialisation can be obtained with the xml consumer
389 - this will provide an xml document which can be used freely in melt and
390 other MLT applications.
392 See mlt-xml.txt for more information.
397 Some filters/transitions should be applied on the output frame regardless
398 of which track it comes from - for example, you might have a 3rd text
399 track or a watermark which you want composited on every frame, and of
400 course, there's the obscure filter....
402 melt only supports this in two invocations - as a simple example:
404 $ melt a.dv -track -blank 100 b.dv -consumer xml:basic.mlt
405 $ melt basic.mlt -filter watermark:watermark.png