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211 lines
7 KiB
Text
211 lines
7 KiB
Text
GStreamer Editing Services
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This is a list of features and goals for the GStreamer Editing
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Services.
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Some features are already implemented, and some others not. When the
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status is not specified, this means it is still not implemented but
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might be investigated.
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FUNDAMENTAL GOALS:
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1) API must be easy to use for simple use-cases. Use and abuse
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convenience methods.
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2) API must allow as many use-cases as possible, not just the simple
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ones.
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* Project file load/save support (GESFormatter)
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Status:
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Implemented, requires API addition for all use-cases.
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Problems:
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Timelines can be stored in many different formats, we need to
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ensure it is as easy/trivial as possible for users to load/save
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those timelines.
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Some timeline formats might have format-specific
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sources/objects/effects which need to be handled in certain ways
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and therefore provide their own classes.
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The object that can save/load GESTimeline are Formatters.
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Formatters can offer support for load-only/save-only formats.
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There must be a list of well-known GES classes that all formatters
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must be able to cope with. If a subclass of one of those classes is
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present in a timeline, the formatter will do its best to store a
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compatible information.
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A Formatter can ask a pre-render of classes that it doesn't
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understand (See Proxy section).
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Formatters can provide subclasses of well-known GES classes when
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filling in the timeline to offer format-specific features.
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* Grouping/Linking of Multiple TrackObjects
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Status:
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Implemented, but doesn't have public API for controlling the
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tracked objects or creating groups from TimelineObject(s)
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Problems:
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In order to make the usage of timelines at the Layer level as easy
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as possible, we must be able to group any TrackObject together as
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one TimelineObject.
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The base GESTimelineObject keeps a reference to all the
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GESTrackObjects it is controlling. It contains a mapping of the
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position of those track objects relatively to the timeline objects.
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TrackObjects will move and be modified synchronously with the
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TimelineObject, and vice-versa.
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TrackObjects can be 'unlocked' from the changes of its controlling
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TimelineObject. In this case, it will not move and be modified
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synchronously with the TimelineObject.
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* Selection support (Extension from Grouping/Linking)
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Problems:
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In order to make user-interface faster to write, we must have a way
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to create selections of user-selected TimelineObject(s) or
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TrackObject(s) to move them together.
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This should be able to do by creating a non-visible (maybe not even
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inserted in the layer?) TimelineObject.
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* Effects support
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TBD (Pending proposal by Thibault)
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* Source Material object
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Problems:
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Several TimelineSource for a same uri actually share a lot
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in common. That information will mostly come from GstDiscoverer,
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but could also contain extra information provided by 3rd party
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modules.
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Definition:
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Material: n, The substance or substances out of which a thing is or
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can be made.
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In order to avoid duplicating that information in every single
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TimelineSource, a 'Material' object needs to be made available.
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A Material object contains all the information which is independent
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of the usage of that material in a timeline.
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A Material object can specify the TimelineSource class to use in a
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Layer.
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* Proxy support
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Problems:
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A certain content might be impossible to edit on a certain setup
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due to many reasons (too complex to decode in realtime, not in
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digital format, not available locally, ...).
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In order to be able to store/export timelines to some formats, one
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might need to have to create a pre-render of some items of the
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timeline, while retaining as much information as possible.
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Content here is not limited to single materials, it could very well
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be a complex combination of materials/effects like a timeline or a
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collection of images.
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To solve this problem, we need a notion of ProxyMaterial.
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It is a subclass of Material and as such provides all the same
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features as Material.
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It should be made easy to create one from an existing TimelineSource
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(and it's associated Material(s)), with specifiable rendering
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settings and output location.
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The user should have the possibility to switch from Proxy materials
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to original (in order to use the lower
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resolution/quality/... version for the editing phase and the
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original material for final rendering phase).
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* Editing modes (Ripple/Roll/Slip/Slide)
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Problems:
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Most editing relies on heavy usage of 4 editing tools which editors
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will require. Ripple/Roll happen on edit points (between two clips)
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and Slip/Slide happen on a clip.
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The Ripple tool allows you to modify the beginning/end of a clip
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and move the neighbour accordingly. This will change the overall
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timeline duration.
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The Roll tool allows you to modify the position of an editing point
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between two clips without modifying the inpoint of the first clip
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nor the out-point of the second clip. This will not change the
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overall timeline duration.
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The Slip tool allows you to modify the in-point of a clip without
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modifying it's duration or position in the timeline.
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The Slide tool allows you to modify the position of a clip in a
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timeline without modifying it's duration or it's in-point, but will
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modify the out-point of the previous clip and in-point of the
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following clip so as not to modify the overall timeline duration.
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These tools can be used both on TimelineObjects and on
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TrackObjects, we need to make sure that changes are propagated
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properly.
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* Coherent handling of Content in different formats
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Problems:
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When mixing content in different format (Aspect-Ratio, Size, color
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depth, number of audio channels, ...), decisions need to be made on
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whether to conform the material to a common format or not, and on
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how to conform that material.
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Conforming the material here means bringing it to a common format.
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* Media Asset Management integration
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(Track, Search, Browse, Push content) TBD
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* Templates
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Problem:
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In order to create as quickly as possible professional-looking
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timelines, we need to provide a way to create 'templates' which
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users can select and have an automatic timeline 'look' used.
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This will allow users to be able to quickly add their clips, set
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titles and have a timeline with a professional look. This is
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similar to the same feature that iMovie offers both on desktop and
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iOS.
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* Plugin system
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Problem:
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All of GES classes are made in such a way that creating new
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sources, effects, templates, formatters, etc... can be easily added
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either to the GES codebase itself or to applications.
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But in order to provide more features without depending on GES
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releases, limit those features to a single application, and in
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order to provide 'closed'/3rd party features, we need to implement
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a plugin system so one can add new features.
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Use a registry system similar to GStreamer.
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