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Michael Zucchi

 B.E. (Comp. Sys. Eng.)

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Monday, 01 April 2013, 07:43

A bit more on jjj

I spent a few spare hours yesterday and today poking at some of the other basic functions needed for an android video editor. First a list of icons that loads asynchronously and then some database stuff.

The asynchronous loading with caching was more involved than i'd hoped but I have it (mostly) working. Unfortunately Android calls getView(0) an awful lot, and often on a view which isn't actually used to show the content, so trying to match views to latent requests doesn't always work (for view 0 only).

I've done something like this before using a thread and request handling queue, but this time I tried just using a threadpool and futures. I tested it by loading individually offset frames from a mp4 file - i.e. it's pretty slow - and the caching works fairly well, i.e. it drops starting of processing frames you've scrolled away from so that the screen refreshes relatively efficiently. The GUI remains smooth and responsive. Apart from the item-0 problem it would be perfectly adequate. And in practice the images would just be loaded from a pre-recorded jpeg so most of the loading latency would vanish.

After that I came up with a fairly reusable class which lets me add 'async image loading and caching' to any list or gridview, which is a necessity on Android to save on memory requirements. I used it to create a graphical clip selector in only a few lines of code.

And today I filled out another big chunk - creating a database to store everything. I tried to keep it as simple as possible but it's still fairly involved. I was thinking of using Lucene just as an index, but then I decided I really did want the referential integrity guaranteed by using Berkeley DB JE. So I used that instead. It's got a really great API for working with POJO's and it's pretty simple to set up complex relational databases using annotations. The only real drawback of using itis that if you need to write complex joins and so on you have to code them by hand: but I don't need them here, and besides often the complex joinery in SQL means you have to write messy code to handle it anyway. It's not something I miss having to deal with.

Then I further hacked up the hackish sequence editor to fit in with the DB backend. Actually I hacked up quite a bit of glue to tie together all the GUI work I have done so far:

The main window is a project window, from which you browse the projects, and create another one. Clicking on a project jumps straight into the scene editor. I'm using a AsyncTaskLoader to open the database which can take a second or so.

A project will have a collection of scenes and probably an output format. Although initially I am only implementing it using a single scene otherwise it seems to add too much complication to the interface.

This is currently the sequence editor as mentioned in the last post. Tracks/layers can be edited using drag and drop. Clicking on the "add clip" brings up the Clip manager, and after a clip is selected it is added to the scene. Changes are persisted to the database as they occur.
Clip manager
This brings up a list of clips which have been defined for the given project. Clicking on a clip just selects it and returns it to the caller (i.e. the Scene). There is also an "add" menu item which then brings up a file requester (using the standard Android Intent for "get content") which lets you choose a video file. Once one is selected, it then jumps to the Clip editor.

The database tracks video files used in a separate table, but i'm not sure adding a separate GUI for that is terribly useful - just clutter really. But the table will be used if I want to transcode videos into a quick-editing format.

Clip Editor
And this is the first interface I mentioned a couple of posts ago. It lets one mark a single region within a video file, and then save it as a clip. The clip is then saved back into the clipmanager.

Its surprising how much junk you have to write to get anything going. It's not like a command line programme where you can just add another switch in a couple of lines of code, you need a whole new activity, layout, intent management, response handling, blah blah etc etc.

So I guess at another two half-days that takes the total effort to about 4, although i should probably round it up to 5 being a bit more conservative. A few hours more to hook in the prototype renderer and I would have a basic video editor done - not bad for a weekend hack, even if it was a particularly super-long weekend ;-). There are of course some fairly important features missing such as transitions and animations and so forth.

Although having it at this level of integration also begins to show up all the usability issues and edge-cases i've ignored until now. It is also where one can investigate alternatives fairly cheaply: e.g. does it really work having clips per-project, or should they be a globally available resource library? This is what prototypes are for, after-all ...

It's also starting to approach the point where the hacking for entertainment starts to turn south; maintaining and fixing vs exploring and creating.

Tagged android, hacking, jjmpeg.
Animated tiles & bigger sprites | jjj sequence editor
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