Re: [Mlt-devel] Date Overlay (aka Dynamic Titles)

[Dan D. <da...@de...>]

On Wed, May 4, 2011 at 7:42 PM, Brian Matherly <pez...@ya...> wrote:
> Hi Dan (and anyone else),
>
> You may remember me from this thread:
> http://www.kinodv.org/dcforum?az=show_topic&forum=101&topic_id=2491&mesg_id=2491&page=#3030
>
> Now that I'm forced to move away from Kino, I went searching to see if
> anyone has put any work into this feature for other NLEs. I didn't find
> anyone working on it, but I found some requests:
>
> Openshot:
> http://www.openshotusers.com/forum/viewtopic.php?f=27&t=528
>
> Kdenlive:
> http://www.kdenlive.org/mantis/view.php?id=643
> http://www.kdenlive.org/mantis/view.php?id=1588
> http://www.kdenlive.org/mantis/view.php?id=1597
> http://www.kdenlive.org/forum/can-kdenlive-display-datetime-info
>
> So I'm here to offer my services to get this feature implemented. I can
> write the code and test it if someone can help me produce a design that will
> fit into the MLT framework and can be accepted into the main codebase.
>
> The plan I have in mind is as follows:
> 1) Implement a dynamic title feature in MLT that provides access to metadata
> that is available from the file attributes that don't require understanding
> the codecs within the file (filename, modification date, etc).

Mlt already has dynamic titles. See the FAQ item about burning in timecode.

> 2) Implement the feature in Kdenlive and Openshot
> 3) Extend libav to extract timecode and date/time metadata from applicable
> codecs and make it available in the API.

This is the hard part. A way to handle DV only is to attach the raw DV
packets to the mlt frames and make a libdv filter that reads the
timecode and date/time and applies them to the mlt frame as metadata
properties.

> 4) Extend MLT to support the new timecode and date/time metadata provided by
> libav for dynamic titles.

done. The data_feed and data_show combo is extensible to any meta
attributes. Also, mlt already supports the FFmpeg AVMetadata API, but
that API is currently stream-oriented and not temporal in nature. If
you look at the discussion forum on mltframework.org, I just had a
discussion with another guy about the inability to support QuickTime
timecode tracks.

> After these steps, Kdenlive and Openshot would match the current dynamic
> title functionality of Kino.
>
> I started to examine the MLT source to get an idea of what it would take to
> implement this feature. I see that titles are typically generated using the
> Gtk2 Pixbuf producer. So it stands to reason that we can simply extend the
> implementation to support dynamic text which can be replaced in an SVG file,

The component that handles dynamic titles is core/filter_data_show.c.
It reads a  mlt properties file. If you still feel the need to use
SVG, you could make make a new data_show that is a generic text
template processor ala web server app technologies.

> and the pixbuf can be re-rendered with each frame using new text. After some
> examination, I think I understand what makes this request non-trivial. The
> producer has no knowledge of other producers. So there is no way for the
> pixbuf producer to know the creation date of file being used by an other
> producer. Maybe there is some hidden trick that I don't know about. Or maybe
> the feature needs to be implemented as a transition so that it has access to
> the frames that it is being mixed with.
>
> So, that's where I'm at. I hope you can afford some time to engage in a
> dialog about how this can be implemented. Maybe you already have something
> in mind.
>
> Please let me know how we can proceed from here.

Get the metadata.

> Regards,
>
> ~Brian
>

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