OggSpots

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== Purpose ==
== Purpose ==
-
Recordings of seminars, lectures and presentations generally consist of slides plus an audio recording of the presentation. Slides are usually (if not animated) just a sequence of images. A very efficient representation of such a recording is then as a stream of images with timing information plus the recorded audio underneath.
+
Recordings of seminars, lectures and presentations generally consist of slides plus an audio recording of the presentation. Slides are usually (if not animated) just a sequence of images. 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 presentation parameters, input image formats and their timing. We encourage in particular the use of <b>PNG</b> as an open [http://www.w3.org/TR/PNG/ image compression format] or of <b>JPG</b>.
+
This specification defines a format to describe a timed image track, including presentation parameters, input image formats and their timing. We encourage in particular the use of the open compression formats [http://www.w3.org/TR/PNG/ PNG] and [http://www.jpeg.org/ JPEG] for lossless and lossy image compression respectively.
-
 
+
-
We define 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.
+
 +
We define 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]], or [[OggPCM]], e.g. using [[Ogg Skeleton]], you end up with a video format that consists of timed images and audio.
== Timed Image Specification Format ==
== Timed Image Specification Format ==
-
The bitstream format for this "codec" should be very simple. It should essentially consist only of a sequence of images preceeded by a header with a simple set of fields to set up the decoding. If at all possible, we will avoid encoding parameters for individual images since this will create an additional intermediate decoding step.
+
The bitstream format for this "codec" should be very simple. It should essentially consist only of a sequence of images preceeded by a header with a simple set of fields to set up the decoding.
-
 
+
-
The following fields are under discussion:
+
-
 
+
-
* Image-Format
+
-
 
+
-
This will specify the image format, e.g. JPEG, GIF. We want to avoid players stumbling over image formats that they do not understand and therefore all images in such a stream need to be of the same format, given in this field.
+
-
 
+
-
* Display-Width, Display-Height
+
-
While it is expected that most of the images in the data packets are of the same size (dimensions, geometry, resolution), variations may occur. A decoder should be given a resolution at which the images are to be presented. Aspect ratio must be kept when images are re-scaled.
 
-
 
-
* Rescaling
 
-
 
-
While images that are larger than the display area defined by Display-Width and Display-Height must be scaled down to this size, this may not necessarily be desirable for smaller images. This paramter decides whether smaller images should be scaled up to meet the display size, or just be displayed inside it.
 
-
 
-
* Align-Horizontal, Align-Vertical
 
-
 
-
Smaller images that are not rescaled to display size may be aligned at several different areas inside the larger display image:
 
-
** Align-Horizontal: centre/left/right
 
-
** Align-Vertical: centre/top/bottom
 
-
 
-
* Background-Colour
 
-
 
-
For transparent images and for smaller, non-rescaled images, the background colour of the images has to be defined. This may be black, white, gray or whatever.
 
-
 
-
 
-
A rough way to author such information could be:
 
-
 
-
Display-Width: 320
 
-
Display-Height: 240
 
-
Rescaling: True
 
-
Background-Colour: Grey
 
-
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
 
Line 55: Line 19:
The first step towards encapsulating the data into ogg is the definition of packets:
The first step towards encapsulating the data into ogg is the definition of packets:
-
* There is a OggSpots ident header, which is encapsulated in the bos page.
+
* There is a OggSpots ident header with setup parameters, which is encapsulated in the bos page.
-
* There is a secondary header packet containing the setup parameters, which is encapsulated in a separate page.
+
* Each image is mapped into a data packet, which are each encoded in their own packet and inserted at the accurate time.
* Each image is mapped into a data packet, which are each encoded in their own packet and inserted at the accurate time.
* The eos page is empty.
* The eos page is empty.
Line 68: Line 31:
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  | Identifier 'SPOTS\0\0\0'                                     | 0-3
+
  | Identifier 'SPOTS\0\0\0'                                     | 0-3
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                              | 4-7
  |                                                              | 4-7
Line 82: Line 45:
  |                                                              | 24-27
  |                                                              | 24-27
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  | Granuleshift  |                                                 28
+
  | Granuleshift  | RESERVED FOR LATER USE                        | 28-31
-
  +-+-+-+-+-+-+-+-+
+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  | ...
+
  | Image-Format                                                  | 32-35
 +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +
|                                                              | 36-39
 +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +
| Display width                | Display height                | 40-43
 +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +
| BG-Color                                                      | 44-47
 +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +
| Align-Horiz  | Align-Vert    | Options                      | 48-51
 +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
The OggSpots <i>version</i>  as described here is major=0 minor=1.
 
-
The <i>granulerate</i> represents the temporal resolution of the logical bitstream in Hz given as a rational number in the same way as the [[OggSkeleton]] fisbone secondary header specifies granulerate. It enables a mapping of granule position of the data pages to time by calculating "granulepos / granulerate".
+
* Version:
 +
The OggSpots version  as described here is major=0 minor=1.
 +
 
 +
* Granulerate & Granuleshift:
 +
The granulerate  represents the temporal resolution of the logical bitstream in Hz given as a rational number in the same way as the [[OggSkeleton]] fisbone secondary header specifies granulerate. It enables a mapping of granule position of the data pages to time by calculating "granulepos / granulerate".
The default granule rate for OggSpots is: 1/30 (30 frames per second resolution).
The default granule rate for OggSpots is: 1/30 (30 frames per second resolution).
-
The <i>granuleshift</i>  is a 1 Byte integer number describing whether to partition the granule_position into two for the OggSpots logical bitstream, and how many of the lower bits to use for the partitioning.  The upper bits then still signify a time-continuous granule position for a directly decodable and presentable data granule.  The lower bits allow for specification of the granule position of a previous OggSpots data packet (i.e. image), which helps to identify how much backwards seeking is necessary to get to the last and still active image. The granuleshift is therefore the log of the maximum possible image spacing.
+
The granuleshift is a 1 Byte integer number describing whether to partition the granule_position into two for the OggSpots logical bitstream, and how many of the lower bits to use for the partitioning.  The upper bits then still signify a time-continuous granule position for a directly decodable and presentable data granule.  The lower bits allow for specification of the granule position of a previous OggSpots data packet (i.e. image), which helps to identify how much backwards seeking is necessary to get to the last and still active image. The granuleshift is therefore the log of the maximum possible image spacing.
The default granule shift used is 32, which halfs the granule position to allow for the backwards pointer.
The default granule shift used is 32, which halfs the granule position to allow for the backwards pointer.
 +
* Image-Format:
 +
 +
The image format specifies e.g. JPEG, GIF. We want to avoid players stumbling over image formats that they do not understand and therefore all image formats used in an OggSpots logical bitstream need to be provided in the bos page.
 +
 +
* Display-Width, Display-Height:
 +
 +
While it is expected that most of the images in the data packets are of the same size (dimensions, geometry, resolution), variations may occur. These fields provide a decoder with a resolution at which the images are to be presented. If images need to be re-scaled, aspect ratio must be kept.
 +
 +
* Background-Colour:
 +
 +
For transparent images and for smaller, non-rescaled images, the background colour of the images has to be defined. This may be black, white, gray or whatever. This is a default setting which may be overruled by the specific image.
 +
 +
* Align-Horizontal, Align-Vertical:
 +
 +
Smaller images that are not rescaled to display size may be aligned at several different areas inside the larger display image:
 +
* Align-Horizontal: centre/left/right
 +
* Align-Vertical: centre/top/bottom
 +
This is a default setting which may be ruled over by the specific image through its own parameters.
 +
 +
* Options:
 +
 +
* Upscaling: This paramter decides whether smaller images should be scaled up to meet the display size, or just be displayed inside it. This is a default setting and can be ruled over by the specific image through its own parameters.
 +
* Downscaling: This paramter decides whether larger images should be scaled down to meet the display size, or just be truncated. This is a default setting and can be ruled over by the specific image through its own parameters.
 +
 +
=== OggSpots data ===
-
=== OggSpots secondary header ===
+
Each data packet contains a byte offset to where the complete image is stored, a set of parameters to describe what to do with the image, and the image itself.
-
This header contains all the setup information for the decoder.  
+
The insertion time is encoded in the granule_pos of the Ogg Page that the image ends on.
   0                  1                  2                  3
   0                  1                  2                  3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  | Image-Format                                                  | 0-3
+
  | Byte Offset                                                  | 0-3
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  |                                                               | 4-7
+
  | Image-Format                                                  | 4-7
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  | Display width                | Display height                | 8-11
+
  |                                                               | 8-11
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
  | BG-Color      | Rescaling    | Align-Horiz  | Align-Vert    | 12-15
+
| Display width                | Display height                | 12-15
 +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 +
  | BG-Color      | Rescaling    | Align-Horiz  | Align-Vert    | 16-19
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
=== OggSpots data ===
 
-
The data packets are simple. Each data packet simply contains a complete image.
 
-
The insertion time (and therefore the granule_pos) is given through the specified time.
+
== Authoring Considerations ==
 +
 
 +
While it is possible to author an OggSpots video through command-line parameters by handing over a set of images and setting parameters, there should also be a means to author it through files.
 +
 
 +
A rough way to author such information could be:
 +
 
 +
Display-Width: 320
 +
Display-Height: 240
 +
Rescaling: True
 +
Background-Colour: Grey
 +
...further parameters...
 +
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
 +
 
 +
[[Category:Ogg Mappings]]

Latest revision as of 23:27, 15 February 2008

Contents

The following is a draft. It is at best incomplete and at worst completely broken. In any case, it is not an "official" Xiph spec/codec, so use with care.


Purpose

Recordings of seminars, lectures and presentations generally consist of slides plus an audio recording of the presentation. Slides are usually (if not animated) just a sequence of images. 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 presentation parameters, input image formats and their timing. We encourage in particular the use of the open compression formats PNG and JPEG for lossless and lossy image compression respectively.

We define 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, or OggPCM, e.g. using Ogg Skeleton, you end up with a video format that consists of timed images and audio.

Timed Image Specification Format

The bitstream format for this "codec" should be very simple. It should essentially consist only of a sequence of images preceeded by a header with a simple set of fields to set up the decoding.


Timed Images Mapping into Ogg

The first step towards encapsulating the data into ogg is the definition of packets:

  • There is a OggSpots ident header with setup parameters, which is encapsulated in the bos page.
  • Each image is mapped into a data packet, which are each encoded in their own packet and inserted at the accurate time.
  • The eos page is empty.


OggSpots ident header

The timed Spots logical bitstream starts with an ident header which is mapped into the OggSpots bos page. The ident header contains all information required to identify the timed Spots bitstream and to set up a timed Spots decoder. It has the following format:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier 'SPOTS\0\0\0'                                      | 0-3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               | 4-7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version major                 | Version minor                 | 8-11
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Granulerate numerator                                         | 12-15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               | 16-19
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Granulerate denominator                                       | 20-23
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               | 24-27
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Granuleshift  | RESERVED FOR LATER USE                        | 28-31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Image-Format                                                  | 32-35
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               | 36-39
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Display width                 | Display height                | 40-43
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BG-Color                                                      | 44-47
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Align-Horiz   | Align-Vert    | Options                       | 48-51
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


  • Version:

The OggSpots version as described here is major=0 minor=1.

  • Granulerate & Granuleshift:

The granulerate represents the temporal resolution of the logical bitstream in Hz given as a rational number in the same way as the OggSkeleton fisbone secondary header specifies granulerate. It enables a mapping of granule position of the data pages to time by calculating "granulepos / granulerate".

The default granule rate for OggSpots is: 1/30 (30 frames per second resolution).

The granuleshift is a 1 Byte integer number describing whether to partition the granule_position into two for the OggSpots logical bitstream, and how many of the lower bits to use for the partitioning. The upper bits then still signify a time-continuous granule position for a directly decodable and presentable data granule. The lower bits allow for specification of the granule position of a previous OggSpots data packet (i.e. image), which helps to identify how much backwards seeking is necessary to get to the last and still active image. The granuleshift is therefore the log of the maximum possible image spacing.

The default granule shift used is 32, which halfs the granule position to allow for the backwards pointer.

  • Image-Format:

The image format specifies e.g. JPEG, GIF. We want to avoid players stumbling over image formats that they do not understand and therefore all image formats used in an OggSpots logical bitstream need to be provided in the bos page.

  • Display-Width, Display-Height:

While it is expected that most of the images in the data packets are of the same size (dimensions, geometry, resolution), variations may occur. These fields provide a decoder with a resolution at which the images are to be presented. If images need to be re-scaled, aspect ratio must be kept.

  • Background-Colour:

For transparent images and for smaller, non-rescaled images, the background colour of the images has to be defined. This may be black, white, gray or whatever. This is a default setting which may be overruled by the specific image.

  • Align-Horizontal, Align-Vertical:

Smaller images that are not rescaled to display size may be aligned at several different areas inside the larger display image:

* Align-Horizontal: centre/left/right
* Align-Vertical: centre/top/bottom

This is a default setting which may be ruled over by the specific image through its own parameters.

  • Options:
* Upscaling: This paramter decides whether smaller images should be scaled up to meet the display size, or just be displayed inside it. This is a default setting and can be ruled over by the specific image through its own parameters.
* Downscaling: This paramter decides whether larger images should be scaled down to meet the display size, or just be truncated. This is a default setting and can be ruled over by the specific image through its own parameters.

OggSpots data

Each data packet contains a byte offset to where the complete image is stored, a set of parameters to describe what to do with the image, and the image itself.

The insertion time is encoded in the granule_pos of the Ogg Page that the image ends on.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Byte Offset                                                   | 0-3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Image-Format                                                  | 4-7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               | 8-11
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Display width                 | Display height                | 12-15
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BG-Color      | Rescaling     | Align-Horiz   | Align-Vert    | 16-19
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Authoring Considerations

While it is possible to author an OggSpots video through command-line parameters by handing over a set of images and setting parameters, there should also be a means to author it through files.

A rough way to author such information could be:

Display-Width: 320
Display-Height: 240
Rescaling: True
Background-Colour: Grey
...further parameters...
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
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