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Accessibility/Video Codecs: Difference between revisions
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< [https://wiki.mozilla.org/Accessibility/Video_Accessibility Back to main video accessibility page] | |||
== Introduction to Video == | == Introduction to Video == | ||
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To multiplex these multiple tracks of data together into one file (or stream), there is a container (or encapsulation format). | To multiplex these multiple tracks of data together into one file (or stream), there is a container (or encapsulation format). | ||
[[Image:Model_Video_Resource.jpg|thumb|600px|Model of a Video Resource (please turn into graphic)]] | |||
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To compress high bandwidth content such as video or audio into a smaller file, there are codecs (encoder/decoder). | To compress high bandwidth content such as video or audio into a smaller file, there are codecs (encoder/decoder). | ||
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== Choosing a Caption Format == | == Choosing a Caption Format == | ||
To encapsulate a data stream of a given codec into a container, you require a container-specific multiplexing rule (also called a "media mapping" in Ogg). The multiplexing rules need to be supported by tools, frameworks, and applications - in particular video players - for both, encoding and decoding. | |||
In theory, given a multiplexing rule, you can put any video codec and any captioning format in any container. However, multiplexing rules don't exist for all codec/container combinations. | In theory, given a multiplexing rule, you can put any video codec and any captioning format in any container. However, multiplexing rules don't exist for all codec/container combinations. | ||
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* Vorbis (audio) | * Vorbis (audio) | ||
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| CMML, Kate | | CMML, Kate (OGM: SRT) | ||
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| MP4 | | MP4 | ||
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At this stage we are not clear which format to use. The solution may be found in one format that supports all the requirements, or in multiple formats with the provisioning of a framework for how to implement and interrelate these formats with each other. We may potentially need to cover new ground, create a new specification and promote it into the different relevant communities. Or the best solution may be to support one of the existing subtitling formats and extend it to cover other accessibility needs. | At this stage we are not clear which format to use. The solution may be found in one format that supports all the requirements, or in multiple formats with the provisioning of a framework for how to implement and interrelate these formats with each other. We may potentially need to cover new ground, create a new specification and promote it into the different relevant communities. Or the best solution may be to support one of the existing subtitling formats and extend it to cover other accessibility needs. | ||
Also, there needs to be a recommendation for how to display the different text codecs on screen, such that a standard means of display for the different types is achieved. | Also, there needs to be a recommendation for how to display the different text codecs on screen, such that a standard means of display for the different types is achieved. | ||
For example: audio annotations - when they are not given as an additional audio track, but rather as text - are not to be displayed as text, but rather be rendered through a text-to-speech with live region semantics so that assistive technologies are notified when there is new text. The user can then configure their assistive technology to show the text via text to speech or on a Braille display. For text-to-speech, the user could also decide what the speech rate should be, and send it to another channel. This means that users could hear audio descriptions at a high TTS rate through a headset and other watchers wouldn't necessarily hear them. | |||
As for the implementation of support for a new text codec, there is a whole swag of software to be extended. | As for the implementation of support for a new text codec, there is a whole swag of software to be extended. | ||
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To enable authoring requires support for ffmpeg, ffmpeg2theora, and further GUI authoring applications to be determined. | To enable authoring requires support for ffmpeg, ffmpeg2theora, and further GUI authoring applications to be determined. | ||
< [https://wiki.mozilla.org/Accessibility/Video_Accessibility Back to main video accessibility page] | |||