2023-09-13 Lumiera Developers Meeting

Ichthyo started to define a collection of FocusTopics. These are topics towards which we focus our attention for further development after the current Engine integration is completed. Some tickets currently of interest were enhanced and extended, and new tickets created, which were all marked with the FocusTopic Tag.

→ See Report-17 in the Lumiera Issue Tracker

Ichthyo identified some difficult issues concerning session modifications and change logging, especially in connection with rules based configuration.

We discussed in some detail event sourcing, session modification, session configuration and representation of a configuration possibly as a context in the session. Of particular interest is the portability of a session from one machine to another and, consequently, the problems that can arise when a change in configuration occurs: these should be recorded as an event in the Event-Log. However, this requires the representation of the entire configuration in a consolidated form as part of The Model. A change in the configuration could then be detected and recorded as an event.

Another task of concern is how the actual Diff Messages will be generated. We could first manipulate the data model and then detect a diff. Yet the favourable solution would be to interpret the commands and directly derive the events associated with the commands, with an attached diff, which can then be applied against the data model as a projection.

A discussion followed to sort out which topics should be addressed first.

It seems the topics regarding Event Log and Session persistence #1234 #540 and #569 should be addressed first, since these may lead to decisions relevant to many other parts of the system. Possibly also #332 regarding a full definition of placement capabilities.

The topic of Placement interpretation will be addressed in the next vertical slice, where we intend to add a clip to the timeline. To do this, we’ll require at least a simple resolution capability of Placements, because we’ll attempt do the groundwork for The Builder.

Benny proposes to add »interface« and »mock« tickets for Event-Log and Placements, blocking the full implementation follow-up tickets. Then these preliminary parts can be addressed first and integrated as part of the »Add Clip« Vertical Slice. For Context: currently the »Playback« Vertical Slice is being worked on, aiming towards a first integration of the Render Engine.

Ichthyo reports on the progress of the »Playback Vertical Slice« effort.

Next steps:

Benny reworked and extended the documentation overview in the Lumiera website. This can be published now. Moreover, Benny investigated Glossary and Index generation. It turns out that ASCIIDOC already provides an index generation feature, which could be configured and used to build an index. But there is no support to generate a glossary which we’ll build soon. The next goal would be to build a prototype for testing and to see how this can be integrated into the website infrastructure.

Benny conducted some research regarding library solutions for video display, notably ffmpeg, GStreamer and libVLC. It was rather easy to code up an "hello world" example based on GStreamer, while it was difficult to find suitable documentation regarding the ffmpeg based solution. Moreover, GStreamer seems to have a much more active and helpful community.

Next steps would be to look in more depth into libVLC, and especially to compare the feature sets of these solutions. Cehteh points out that MPV (formerly MPlayer) would also be an interesting point of reference. Benny mentions that GTK4 offers an integrated video display capability. We’ll investigate these frameworks further.

Extended discussion ensued regarding video frameworks and the difficulties regarding the plethora of interfaces, especially when it comes to hardware acceleration support. Ideally, the Lumiera project should follow the solutions provided by a sufficiently active community, capable of following the constant evolution of interfaces and frameworks.

It was agreed upon that the »Playback Vertical Slice« just needs a very simple solution to output raw video (RGB888 or YUV), and offers a good opportunity for experimentation to find a suitable support framework.

The next meeting will be Wednesday Oct 11, 20:00 UTC. You are welcome to join.