Pete's Alley - DaisyTalks

Written by Rich Morin.

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Path:  AreasContentOverviews

Precis:  processing presentation videos into DAISY

Presentation videos typically contain inaccessible content. DaisyTalks is a speculative project aimed at processing these into DAISY or other accessible formats. As usual, comments and suggestions are welcome.


For a number of years, various organizations have been recording and distributing videos of slideshow-based presentations (e.g., technical talks). The quality of these videos varies widely, of course, but many are interesting and well produced. For example, over the last several years, Confreaks has been recording, editing, and distributing high-quality videos of conference presentations. They currently have more then 15,000 videos in their collection.

Because there are many distributors for this sort of content, I would guess that there are hundreds of thousands of videos online, including conference and meeting presentations, university offerings, etc. I’ve watched a large number of these videos, often with great interest and pleasure. Indeed, the ability to “attend” conferences remotely, at my own pace, is one of the marvels of the age.

A well-edited conference video typically contains audio and video of the speaker(s), along with images of presented slides. There may also be embedded dynamic content, including live coding, prerecorded videos, etc. Although I can simply sit back and watch the video, the controls on the presenting web page offer other possibilities. For example, I can pause the video to examine or consider a slide, go back to an earlier point in the presentation, etc.


Unfortunately, many of these videos contain inaccessible content, so they can’t be enjoyed fully by impaired “viewers”. Slides are the most common roadblock for the vision-impaired users; others include animations, screencasts, and terminal sessions. For that matter, the audio content isn’t accessible to the deaf and “background” music can make it difficult to understand the speaker.

More generally, the lack of computer-friendly metadata gets in the way of machine-assisted retrieval or viewing. For example, I can’t perform a text-based search on any of this material, let alone peruse an index or table of contents. I’ve been thinking about ways to make this material more accessible, convenient, and navigable. The following notes summarize my current thinking; as usual, comments and suggestions are welcome!


A combination of existing open source tooling and crowdsourced effort can supplement videos with metadata and alternative formats, including audio and video transcriptions, keywords, etc. Using this material, more accessible and navigable presentations can be produced.

My preferred approach is to capture information from slides and speech, using mechanized means (e.g., Optical Character Recognition). When this approach runs into trouble (e.g., describing an image), we can fall back on human effort to augment and edit the collected information. Following the approach taken in Pete’s Alley, we will encode much of this information in structured, text-based files (e.g., TOML with Markdown inclusions).

Once we have all of the information we can harvest, we can use it to generate distribution formats. HTML is an obvious target, because it can make the material available without requiring the user to install special “reader” software. However, DAISY is also a strong contender:

DAISY (Digital Accessible Information SYstem) is a technical standard for digital audiobooks, periodicals, and computerized text. DAISY is designed to be a complete audio substitute for print material and is specifically designed for use by people with “print disabilities”, including blindness, impaired vision, and dyslexia. Based on the MP3 and XML formats, the DAISY format has advanced features in addition to those of a traditional audio book. Users can search, place bookmarks, precisely navigate line by line, and regulate the speaking speed without distortion. DAISY also provides aurally accessible tables, references, and additional information. As a result, DAISY allows visually impaired listeners to navigate something as complex as an encyclopedia or textbook, otherwise impossible using conventional audio recordings.

DAISY Digital Talking Book


Processing Steps

Here’s a hand-waving precis of the processsing steps:

Data Flow


Typically, conference videos are not set up for easy downloading. Although there are workarounds that can be used for experimentation, any “production” approach would require support of the distributors. That is, they would have to allow downloading of both the current video content and any transformed version.

Audio Content

Extraction of audio content from videos is a fairly common problem, so there are a number of tools to do this job. Once we have the content, we can process it in various ways, as:

Slide Extraction

The first step in processing the video into an accessible format is to turn it into a series of frames. The FFmpeg suite of utilities and libraries seems to be the Golden Path for this. The libraries have C APIs, so they can be linked to Crystal code. This will let us acquire the slides and process them in an efficient manner, while using Ruby-like syntax.

The slide images are embedded in the video content. Typically, they occupy a roughly rectangular area, accompanied by coverage of the presenter and surrounding material (e.g., banners, logos) from the producer. So, our first task in extracting slides is to figure out what part of the screen they occupy.

The screen image is a rectangular array of pixels, each of which contains values for color and intensity. This is encoded as a three-byte RGB triplet, containing intensity values for red, green, and blue.

By storing recent images in a sliding window, we can calculate and retain statistical measures (e.g., variance) of their behavior. Using these, we can characterize portions of the screen. For example:

Once we have determined the extents of the “slides” area, we can look for a “significant” changes (e.g., more than a few pixels changing):

Slide Analysis

Once the slide image is available, we can hand it to Optical Character Recognition (OCR) software for the first stage of analysis. The HTML-based hOCR format encodes text, style, layout information, recognition confidence metrics, etc. Here are some open source OCR packages that support hOCR as an output format:

The layout information that hOCR provides is geometric, rather than semantic. So, for example, it will tell us that a line of text occupies a rectangle in a specified location. Based on this information and some simple heuristics, we should be able to generate semantic HTML (e.g., ul, li) that largely replicates the geometric layout.

Dealing with more complicated images is, of course, an AI-complete problem. However, we should be able to deal with many slides via human effort (e.g., crowdsourcing).

Speech Recognition

Given that we have the presenter’s audio track, it should be possible to generate a first cut at a transcript by means of speech recognition software.

To be continued…