2008 Architectural Redesign/Design Thoughts

This is a listing, not entirely sorted, of thoughts, remarks, things to do, regarding PiTiVi's design, uses, etc...

Eventually, these ideas/thoughts/remarks ... will end up being split up for a full-size (re)design/refactor document.

They could be sorted as following:

  • Coding Style : Urgent
  • Core Features
  • (long term) goals
  • Vision (use cases ?)

Code Review

  • What is too slow ?
  • What is not flexible enough ?
  • What is not re-usable ?
  • What is hard to use ?
  • What is unclear ?
  • What is not needed ?
  • What is in the wrong location ?
    • Split up code

Actual inline-review done in the 'code-review' branch here : http://gitorious.org/projects/pitivi/repos/mainline

Fundamental issues and goals

These issues/goals are not ordered, since they are all equally important.

  • No code shall access private values directly
    • Use setter/getter and python 'property' mapper
    • Ex: myprop = property(_get_myprop,_set_myprop)
  • Core code shall NOT contain any UI-specific code (and vice-versa)
    • This breaks the fundamental Core/UI separation
    • Any code in core that has ui-specific code should be moved to pitivi.ui modules
    • And the opposite for core code in the UI (ex. pitivi.ui.plumber)
  • All Core/UI classes can be subclassable for specific usage
    • This is essential for full pitivi flexibility, for having all kinds of plugins, for having different UI, etc...
  • Splitup code in subdirectories/submodules
    • Maybe not as much as one class per file... but that would be a good goal
    • Definitely ONE base class per file though
  • UI is NOT compulsory ==> pitivi can be used as a LIBRARY
    • There are several tools for which we need all the code from pitivi core without a UI implementation
    • Ex : rendering backends, command-line/scripting tools, ....
    • Disambiguate the naming somewhere
      • pitivi : python module/library
      • PiTiVi : application using the pitivi module
    • Still, we should have most of the UI logic in that library, but without any forced implementation (like qt/gtk/win32...)
  • No gnome/gtk/gobject/gst specific code in base classes
    • This should go in subclasses
    • Create our own event-based interface (to remove dependency on gobject.GObject)
      • Johan might have ideas about this
  • Use generators/yield wherever it can be applied
    • Speedup and memory usage improvement
  • The only HARD DEPENDENCIES of pitivi are python core libraries and gstreamer
    • All other dependencies are optional and should be used from plugins
  • Remove the global instance code
    • No code should depend on a single instance of application and project
    • Needed to be able to load many projects in one instance (amongst other things)
    • The majority of the pitivi module should be non-application modules
  • Unit tests for pitivi core

Code Review

Not at all sorted

File save/load

It seriously needs to be rethinked.

  • Allow formats to create their own subclasses of core classes
    • Subclassing FileSource to add format-specific information
    • Subclassing FileSourceWidget to show that format-specific information in the UI
  • Pluggable format support
  • See Undo/Redo
  • We need a native PiTiVi format
  • Need to be able to save files used in the project
  • Handle files/directories being moved, or loading the project on a different computer
  • Simple support for playlists (ELD, PLS, ASX ?)

Undo/Redo

  • Some actions might be specific to a plugin

Layer support in compositions

  • This is currently implemented using hacks

TimelineObjects

  • Actually use ObjectFactory for producing its content
  • Remove limitation of only one brother per object
  • Allow re-using indentical source/composition many times in a composition
    • Fully synchronized (modifications to one instance are spread to all instances)
    • Not synchronized (they're copies)
    • Half synchronized (only some properties modifications are synchronized to all instances)

ObjectFactory

  • Clarify its usage
    • It contains the global information of objects you can use in the timeline
    • For *any* object you can use in the timeline (source, fx, transition, composition, etc....)
  • Create notion of SubObjectFactory
    • They use a smaller area/time of the parent object (cutting a captured video)
    • Or they could be corrected/modified versions of the original source (i.e. they have extra effects applied to the source)
      • Colour balance correction
      • Audio Correction
      • Media conversion (ex : Use goom to make a video stream out of an audio track)
        • The 'media-converted' ones could maybe done on the fly if you add a file of a given media type (ex:audio) into a track of anothe media type (ex:video).
  • Allow easy transcoding, re-rendering or re-muxing of SubObjectFactory.
  • Allow adding extra (meta)data

Logging

  • Switch to a smarter and more efficient debugging system
    • Use logging module ?
    • do as flumotion ?

Plugin system

  • Figure out how to cleanly solve the problem of plugins extending both CORE and UI classes
    • flumotion use some kind of bundles for this

SmartBin and Playground

This was originally created to cope with 0.8 issues

  • Do we still need the playground ??
  • SmartBin isn't flexible enough
    • We might need to have more than two running at the same time
    • Doesn't support being connected to more than one sink
    • Need to support features like Viewing Video while recording Video AND Audio

An idea might be to have Producers and Consumers.

  • Producer
    • Can be a Timeline, live stream, File source, camera, webcam ,... (more or less like SmartBin now)
    • It has a clean way of querying what it can produce
    • We can connect multiple times to a stream (Audio, Video, ...) it produces
  • Consumer
    • Can be an Encoder, Hardware sinks, Raw File renderer, Network Stream renderer, ...
    • Has a buffering property

Naming inconsistencies

Make sure the naming is coherent and comprehensible

  • Get rid of the notions of 'threads' in bins (sooooo 0.8)
  • Use proper naming from the editing world
  • Add a glossary in the documentation

Temporary files

Thumbnails, captures, etc...

  • Where do we store them ?
  • How do we manage them ?

Hardware source and sinks

  • Move plumber to core
  • Have some discovery utility (i.e. several audio/video sinks)
    • Have it subclassable
      • Use HAL on linux
      • Use ??? on win, etc....
  • Have some generic classification system (os/system agnostic)
    • Audio
    • Video
    • Source
      • Local
      • Camera
      • Network
    • Sink
      • Local
      • Network
    • ???
  • See SmartBin and Playground above

Cache rendering

  • needed for complex videos/operation
  • Have a caching system for frame forward/backward operation
    • Would act like a queue, except it would intercept seeks, do the original one, then do a second [1s before, 1s after] seek to have the data available straight away for step-by-step seeking

Losless editing

  • For I-frame only codecs (DV, JPEG,...), we should be able to only decode/process/encode parts that have be modified
    • Would require gnonlin and core pitivi classes to support non-raw streams

Capture support

  • Have base classes for capture support in core
  • See Hardware source and sinks
  • We absolutely need support for DV and HDV

Flexible 'source provider/browser' support

Currently we only get sources from local files (even worse, it's using gnome-specific things)

  • Make it generic

  • It provides ObjectFactory objects

  • Allow acces to various kinds of source provider

    • Local providers (filesystem, F-Spot, Gnome media (SoC project), ...)
    • Network providers (Media Asset Management)
    • P2P ? Using telepathy and tubes ?
  • Source providers might have extra information ==> ObjectFactory subclasses

  • Figure out what's the best way to solve this issue

    1. Use a source provider (let's say youtube) and grab some files
    2. You want to modify those files (let's say apply a colourbalance, or cut out what you need) to have SubObjectFactory
    3. You save your project (where/how do you save those files ? Do we leave them as a youtube link ?)
    4. You reload your project... but you don't need the youtube browser anymore (you've already got your sources)
      • PROBLEM Disambiguate SourceProvider and SourceBrowser. I'd say the difference is that stuff from SourceProvider(s) have to be moved in the SourceBrowser before being used in the timeline.
  • See also the ideas in ObjectFactory above

Marker points / KeyFrames

Here keyframes are not I-frames but 'key positions'

  • Add support in:
    • ObjectFactory (interesting points, user-introduced data, could be stored with/along the file...)
    • TimelineObject (instance specific property modification)
    • UI

Source flexibility

  • Support multiple versions of one source
    • Ex :
      • low resolution versus HD/4K
      • Distributed/P2P files (first download lowest resolution)
    • Use thumbnail when file not available yet.
  • if it's a network URI, option to save it locally
    • detect if remote source has changed
  • Support for separate index (save/load support)
  • Add basic tests to make sure the sources will behave properly with pitivi
    • ex : testing seeking support
    • If not, propose transcoding, or plugin to download, etc...

Multiple Video support

There's two different use-cases in fact

  • Steroscopic or multi-angle support (multiple video tracks)
  • Editing together multiple videos from the same scene (one video track)
    • You want a way to view all the input videos at the same time, synchronized, so you know which ones to select at any given point
    • This of it as a non-live mixing-desk

Effect support

  • Have a gst_launch plugin where users can create their own freeform effect pipeline
  • Allow concatenation/coupling of existing effects into a bigger one
    • Bonus for adding some scripting in it !
  • Have Audio+Video effects
    • They're in fact two/more separate effects that have synchronization
    • Ex : photo flash effect : you want to have the 'flash' sound in sync with the 'whiteout'/still frame on the video side

Scripting/Template/Scenario system

Allow easy creation of (parts of) the Timeline

  • Should have a clean content/Script separation
    • Ex : Interview script : have the interview person's name separated from the actual video on which to overlay his name
  • Allow subclassing
    • Ex : You can create different ways of displaying the interviewee's name, different ways to blend in/out, ...
  • Have a repository for those scripts/scenarios
    • People can easily share/use/reuse existing scenarios

Text/Subtitle support

How do we handle this properly ?

  • Text track ?
  • Use case : karaoke/subtitle overlay

Missing feature support

Allow cleanly support Projects using unavailable subclasses/plugins/effects.

  • Might not be available
  • Might be proprietary/custom
  • Older version of PiTiVi
    • Provide a way to upgrade the feature/plugin

Central/Distributed repository of PiTiVi plugins

Missing (GStreamer) plugin support

Distributions should support this !

Easy transcoding of sources

  • Allow transcoding sources only
  • Useful also for making sources more editing-friendly
  • Or to have lower resolution versions to work with

GNonLin

Optimize the following use cases

  • Resizing/Trimming
    • By end (modifying media_duration + duration)
    • By beginning (modifying media_start+start+media_duration+duration)
  • Moving many objects at once

One idea for this would be to have a 'block-rebuild' property on GnlComposition that would mark down that is has (or not) to rebuild the internal stack, but postpone it until the property has been set back to False.

GStreamer

  • interlaced support
    • caps (differentiate raw frame/fields)
    • Buffer Flags (TFF, Repeat)
    • ... and obviously support in virtually all relevent plugins
  • Perfect Profesionnal Colourspace support
    • Various Subsampling + Chroma placement (right now we don't make a difference between 4:2:0 jpeg/mpeg2/dv-ntsc ... whereas they have different chroma placement)
    • Various Clamping matrices (HDYC for example)
    • FAST and bit-accurate converters
      • This might require making a generic colourspace converter bin which searches all required/available colourspace converters

Website

  • We need more screenshots
  • Propose nightly builds

Use Cases

These are some (long term) ideas I have

Effect ideas

  • GoogleMaps/OpenStreetMap plugin
    • Use maps to show a trip
    • Zoom-in/zoom-out/move from location to location between the various steps
    • Could use photo geotags to automatically known where to go
  • Photo Flash
    • Could be a nice way to do transitions when doing slideshows
    • Could have a 'flash' sound on the audio track, sync-ed with it
  • Film-reel at slow-speed
    • Start from a still frame/picture
    • Gradually speed up the movie
    • You see the 'film-reel border' moving (i.e. at some points the inter-frame black borders will be visible)
    • Have a flickering soundtrack

The results of the search are