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PNG is an open image compression format that is used as the basis for a "timed image" codec in this specification. Recordings of seminars, lectures and presentations generally consist of slides and a very efficient representation of such a recording is as a stream of images with timing information plus the recorded audio underneath.

This specification defines a format to describe a timed image track, including the presentation parameters, the input images and their timing. It then defines a logical bitstream format for encapsulating the images inside Ogg. When multiplexed together with one of the Xiph audio codecs such as Speex, Vorbis, FLAC, and OggPCM2, e.g. using OggSkeleton, you end up with a video format that consists of timed images and audio.

Timed Image Specification Format

An authoring format for specifying "timed images" has to be defined.

One option is a plain text format. Something along the lines of:

Display-Width: 320
Display-Height: 240
npt:00:00:00.000 /my_slides/image_01.png
npt:00:02:10.000 /my_slides/image_02.png
npt:00:05:02.000 /my_slides/image_03.png
npt:00:06:50.000 /my_slides/image_04.png

could be a simple solution.

A different option is to use a XML based format, something like a "timed image codec":

   <param name="Display-Width"  value="320"/>
   <param name="Display-Height" value="240"/>
   <param name="Image-Format" value="image/png"/>
  <clip start="npt:00:00:00" src="/my_slides/image_01.png"/>
  <clip start="npt:02:10:00" src="/my_slides/image_02.png"/>
  <clip start="npt:05:02:00" src="/my_slides/image_03.png"/>
  <clip start="npt:06:50:00" src="/my_slides/image_04.png"/>

Advantages/disadvantages of these option needs to be discussed.

Timed Images Mapping into Ogg