X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=docs%2Fframework.txt;h=56610fd5b23d46d58daf1bad1de2a390eb761d63;hb=5a9b3541e147a343c998b286ada0c87293354d7c;hp=4aa6e346ba806e75ec41e78abd298f53612eb64f;hpb=be092fb725a3ef83741bb72460e11aac95989e3c;p=mlt diff --git a/docs/framework.txt b/docs/framework.txt index 4aa6e346..56610fd5 100644 --- a/docs/framework.txt +++ b/docs/framework.txt @@ -1,8 +1,8 @@ Framework Documentation -Copyright (C) 2004 Ushodaya Enterprises Limited +Copyright (C) 2004-2009 Ushodaya Enterprises Limited Author: Charles Yates -Last Revision: 2004-03-20 +Last Revision: 2005-05-08 MLT FRAMEWORK @@ -44,7 +44,7 @@ Target Audience: opposed to the implementation details. It is not required reading for the MLT client/server integration - please - refer to valerie.txt and dvcp.txt for more details on this area. + refer to libmvsp.txt and mvsp.txt for more details on this area. SECTION 1 - BASIC OVERVIEW @@ -187,12 +187,12 @@ Hello World: The defaults requested here are a special case - the NULL usage requests that we use the default producers and consumers. - The default producer is "fezzik". This producer matches file names to + The default producer is "loader". This producer matches file names to locate a service to use and attaches 'normalising filters' (such as scalers, deinterlacers, resamplers and field normalisers) to the loaded content - these filters ensure that the consumer gets what it asks for. - The default consumer is "sdl". The combination of fezzik and sdl will + The default consumer is "sdl". The combination of loader and sdl will provide a media player. In this example, we connect the producer and then start the consumer. We @@ -205,11 +205,11 @@ Hello World: Also note, you can override the defaults as follows: - $ MLT_CONSUMER=westley ./hello file.avi + $ MLT_CONSUMER=xml ./hello file.avi - This will create a westley xml document on stdout. + This will create a XML document on stdout. - $ MLT_CONSUMER=westley MLT_PRODUCER=avformat ./hello file.avi + $ MLT_CONSUMER=xml MLT_PRODUCER=avformat ./hello file.avi This will play the video using the avformat producer directly, thus it will bypass the normalising functions. @@ -256,7 +256,7 @@ Factories: +------------------+------------------------------------+------------------+ |MLT_NORMALISATION |The normalisation of the system |PAL or NTSC | +------------------+------------------------------------+------------------+ - |MLT_PRODUCER |The default producer |"fezzik" or other | + |MLT_PRODUCER |The default producer |"loader" or other | +------------------+------------------------------------+------------------+ |MLT_CONSUMER |The default consumer |"sdl" or other | +------------------+------------------------------------+------------------+ @@ -323,8 +323,8 @@ Playlists: // Add it to the playlist mlt_playlist_append( playlist, producer ); - // Close the producer (see below) - mlt_producer_close( producer ); + // Close the producer (see below) + mlt_producer_close( producer ); } // Return the playlist as a producer @@ -389,6 +389,193 @@ Filters: section, even multiple tracks have a single track output. +Attached Filters: + + All services can have attached filters. + + Consider the following example: + + // Create a producer + mlt_producer producer = mlt_factory_producer( NULL, clip ); + + // Get the service object of the producer + mlt_producer service = mlt_producer_service( producer ); + + // Create a filter + mlt_filter filter = mlt_factory_filter( "greyscale" ); + + // Create a playlist + mlt_playlist playlist = mlt_playlist_init( ); + + // Attach the filter to the producer + mlt_service_attach( producer, filter ); + + // Construct a playlist with various cuts from the producer + mlt_playlist_append_io( producer, 0, 99 ); + mlt_playlist_append_io( producer, 450, 499 ); + mlt_playlist_append_io( producer, 200, 399 ); + + // We can close the producer and filter now + mlt_producer_close( producer ); + mlt_filter_close( filter ); + + When this is played out, the greyscale filter will be executed for each frame + in the playlist which comes from that producer. + + Further, each cut can have their own filters attached which are executed after + the producer's filters. As an example: + + // Create a new filter + filter = mlt_factory_filter( "invert", NULL ); + + // Get the second 'clip' in the playlist + producer = mlt_playlist_get_clip( 1 ); + + // Get the service object of the clip + service = mlt_producer_service( producer ); + + // Attach the filter + mlt_service_attach( producer, filter ); + + // Close the filter + mlt_filter_close( filter ); + + Even the playlist itself can have an attached filter: + + // Create a new filter + filter = mlt_factory_filter( "watermark", "+Hello.txt" ); + + // Get the service object of the playlist + service = mlt_playlist_service( playlist ); + + // Attach the filter + mlt_service_attach( service, filter ); + + // Close the filter + mlt_filter_close( filter ); + + And, of course, the playlist, being a producer, can be cut up and placed on + another playlist, and filters can be attached to those cuts or on the new + playlist itself and so on ad nauseum. + + The main advantage of attached filters is that they remain attached and don't + suffer from the maintenance problems associated with items being inserted and + displacing calculated in/out points - this being a major issue if you + exclusively use the connect or insert detached filters in a multitrack field + (described below). + + +Introducing the Mix: + + The mix is the simplest way to introduce transitions between adjacent clips + on a playlist. + + Consider the following playlist: + + +-+----------------------+----------------------------+-+ + |X|A |B |X| + +-+----------------------+----------------------------+-+ + + Let's assume that the 'X' is a 'black clip' of 50 frames long. + + When you play this out, you'll get a 50 frames of black, abrupt cut into + A, followed by an abrupt cut into B, and finally into black again. + + The intention is to convert this playlist into something like: + + +-+---------------------+-+------------------------+-+ + |X|A |A|B |B| + |A| |B| |X| + +-+---------------------+-+------------------------+-+ + + Where the clips which refer to 2 clips represent a transition. Notice that + the representation of the second playlist is shorter than the first - this is + to be expected - a single transition of 50 frames between two clips will + reduce the playtime of the result by 50 frames. + + This is done via the use of the mlt_playlist_mix method. So, assuming you get + a playlist as shown in the original diagram, to do the first mix, you could do + something like: + + // Create a transition + mlt_transition transition = mlt_factor_transition( "luma", NULL ); + + // Mix the first and second clips for 50 + mlt_playlist_mix( playlist, 0, 50, transition ); + + // Close the transition + mlt_transition_close( transition ); + + This would give you the first transition, subsequently, you would apply a similar + technique to mix clips 1 and 2. Note that this would create a new clip on the + playlist, so the next mix would be between 3 and 4. + + As a general hint, to simplify the requirement to know the next clip index, + you might find the following simpler: + + // Get the number of clips on the playlist + int i = mlt_playlist_count( ); + + // Iterate through them in reverse order + while ( i -- ) + { + // Create a transition + mlt_transition transition = mlt_factor_transition( "luma", NULL ); + + // Mix the first and second clips for 50 + mlt_playlist_mix( playlist, i, 50, transition ); + + // Close the transition + mlt_transition_close( transition ); + } + + There are other techniques, like using the mlt_playlist_join between the + current clip and the newly created one (you can determine if a new clip was + created by comparing the playlist length before and after the mix call). + + Internally, the mlt_playlist_mix call generates a tractor and multitrack as + described below. Like the attached filters, the mix makes life very simple + when you're inserting items into the playlist. + + Also note that it allows a simpler user interface - instead of enforcing the + use of a complex multitrack object, you can do many operations on a single + track. Thus, additional tracks can be used to introduce audio dubs, mixes + or composites which are independently positioned and aren't affected by + manipulations on other tracks. But hey, if you want a bombastic, confusing + and ultimately frustrating traditional NLE experience, that functionality + is provided too ;-). + + +Practicalities and Optimisations: + + In the previous two sections I've introduced some powerful functionality + designed to simplify MLT usage. However, a general issue comes into this - + what happens when you introduce a transition between two cuts from the same + bit of video footage? + + Anyone who is familiar with video compression will be aware that seeking + isn't always without consequence from a performance point of view. So if + you happen to require two frames from the same clip for a transition, the + processing is going to be excessive and the result will undoubtedly be very + unpleasant, especially if you're rendering in realtime... + + So how do we get round this? + + Actually, it's very simple - you invoke mlt_producer_optimise on the top + level object after a modification and MLT will determine how to handle it. + Internally, it determines the maximum number of overlapping instances + throughout the object and creates clones and assigns clone indexes as + required. + + In the mix example above, you can simply call: + + // Optimise the playlist + mlt_producer_optimise( mlt_playlist_producer( playlist ) ); + + after the mix calls have be done. Note that this is automatically applied + to deserialised MLT XML. + + Multiple Tracks and Transitions: MLT's approach to multiple tracks is governed by two requirements: @@ -512,8 +699,8 @@ Multiple Tracks and Transitions: mlt_producer create_tracks( int argc, char **argv ) { - // Create the tractor - mlt_tractor tractor = mlt_tractor_new( ); + // Create the tractor + mlt_tractor tractor = mlt_tractor_new( ); // Obtain the field mlt_field field = mlt_tractor_field( tractor ); @@ -522,13 +709,13 @@ Multiple Tracks and Transitions: mlt_multitrack multitrack = mlt_tractor_multitrack( tractor ); // Create a composite transition - mlt_transition transition = mlt_factory_transition( "composite", "10%,10%:15%x15%" ); + mlt_transition transition = mlt_factory_transition( "composite", "10%/10%:15%x15%" ); // Create track 0 mlt_producer track0 = create_playlist( argc, argv ); - // Create the watermark track - note we NEED fezzik for scaling here - mlt_producer track1 = mlt_factory_producer( "fezzik", "pango" ); + // Create the watermark track - note we NEED loader for scaling here + mlt_producer track1 = mlt_factory_producer( "loader", "pango" ); // Get the length of track0 mlt_position length = mlt_producer_get_playtime( track0 ); @@ -554,10 +741,10 @@ Multiple Tracks and Transitions: // Now plant the transition mlt_field_plant_transition( field, transition, 0, 1 ); - // Close our references - mlt_producer_close( track0 ); - mlt_producer_close( track1 ); - mlt_transition_close( transition ); + // Close our references + mlt_producer_close( track0 ); + mlt_producer_close( track1 ); + mlt_transition_close( transition ); // Return the tractor return mlt_tractor_producer( tractor ); @@ -992,7 +1179,7 @@ mlt_service: A service does not define any properties when constructed. It should be noted that producers, filters and transitions my be serialised (say, via the - westley consumer), and care should be taken to distinguish between + xml consumer), and care should be taken to distinguish between serialisable and transient properties. The convention used is to prefix transient properties with an underscore.