Welcome to the Lurker's Guide to Video, a repository for the little-known, undocumented knowledge that you need in order to write any sort of useful video software.

The Lurker's Guide began in the 1990s as a guide to video software on SGI (Silicon Graphics) machines. Although SGI is long gone, several of the articles continue to be popular and relevant as they explain videosyncrasies that still apply today; you can find those articles just below, followed by the original SGI Lurker's Guide.

History

The name is a reference to the lowly poor folk who squat in the dark lower decks of the spaceship on the sci-fi series Babylon 5.

The Lurker's Guide to Video on SGI Machines

This collection of documents does not represent SGI, and is not an official SGI publication. The entire contents of this document are the personal observations, and/or opinions, of the lurkers. All errors and opinions in it are ours alone. SGI makes no guarantees about anything in this document. Neither do the lurkers. You use it at your own risk.

Video on SGI and in General: Concepts, Definitions and Parameters

• What Are the SGI Video Devices?
  • Product and codenames you'll see in the Lurker's Guide
• What Are the SGI Video-Related Libraries?
  • Abbreviations you'll see in the Lurker's Guide
  • Classic, O2, and cross-platform buffering APIs
• Fields: Why Video Is Crucially Different from Graphics
  • Explains crucial video concepts and conventions
• Definitions: F1/F2, Interleave, Field Dominance, and More
  • Defines F1, F2 for 525- and 625-line video standards
  • Explains how F1/F2 fields should be interleaved
  • Defines field dominance, explains why it matters
  • The terrible terms: "even" and "odd"
  • Defines related SGI Movie Library concepts
• Where Does Field Dominance Originate?
  • What has field dominance? A tape? A signal? When is field dominance determined?
  • Who has to worry about field dominance?
  • What idiot came up with this field dominance thing anyway?
  • Field dominance and 3:2 pulldown
• How Big Is Video?
  • How Many Bytes Per Pixel?
  • How Many Pixels In a Field/Frame?
  • How Many Bytes In a Field/Frame?
  • How Many Fields/Frames per Second?
  • How Many Bytes Per Second in Full-Rate Video?
• Square and Non-Square Pixels
  • What are non-square pixels? Why do I care?
  • What is the pixel aspect ratio of non-square pixels?
• The Pixel Rosetta Stone: Packings and Colorspaces
  • How video and graphics pixels are laid out in memory
  • Tokens you'll see in VL, OpenGL, IRIS GL, DM (dmParams, dmIC, dmColor, libmoviefile, libmovieplay, ...), and CL
• Timecode
  • Timecode as a Numbering Scheme
  • Timecode as a Data Stamp in a Computer
  • Timecode as a Signal over a Wire
  • Timecode as a Signal on a Tape

Tips for Writing SGI Video Applications

• Displaying In-Memory Video Using OpenGL
  • How to make OpenGL glDrawPixels() go as fast as possible
  • Useful for vino, ev3, cosmo2, Sirius, and many future boards
  • Displaying Video on O2 using the OpenGL interlace and YCrCb extensions
• Displaying Video Using Galileo (ev1)
  • Setting up and maintaining an ev1 display
• Tips for Writing Your Main (select, event) Loop
  • Explains what the VL file descriptors do
  • Avoiding common pitfalls when writing a VL select() loop
  • How to make it work if you're stuck with XtMainLoop()
  • Some caveats about spinloops
  • How to detect dropped or duplicated data correctly
• Choosing an Input Jack
  • Ready-to-steal sample code for making this task as simple as it should be
• Hints for Vid-to-Mem Applications
  • Video source node controls
  • Memory drain node controls
  • Handling preemption
• Multi-Threaded Apps and the VL
  • The multithreaded process coordination rules.
• Seizing Higher Scheduling Priority
  • How to use schedctl(2) to get better average response
• Motion JPEG on SGI Systems
  • An epic tale of bravery and conquest

SGI Video Devices

• Taxonomy of the ev1 and cosmo1 Boards
  • What are all those boards like Galileo Video, Indy Video, and Indigo2 Video, and how are they different?
  • What jacks do they have?
  • How does Cosmo Compress fit in?
• Taxonomy of the ev3 and cosmo2 Boards
  • What is Impact Video?
  • What is Impact Compression?
  • What happened to ev2?
• Notes on Video Input for O2 Systems (mvp)
  • MVP input jacks
  • Programming video to memory transfer
  • Dealing with the O2 Camera
• Old (Pre-1994) SGI Video Boards
  • Video Framer
  • VideoLab
  • VideoSplitter
  • Live Video Digitizer
  • Broadcast Video Option (BVO)
  • Video Creator

Video and OpenGL on O2

• DMbuffers for Video and OpenGL
  • What is a dmbuffer?
  • What are the relevant image formats?
  • How do you set up a pool of buffers?
  • How to you use them with video?
  • How do you use them with graphics?
• Rendering graphics onto video
  • How the video path is set up.
  • How graphics is set up.
  • How to handle fields with stencils.
  • How to handle fields with glPixelZoom and glCopyPixels
  • Rendering in the YCrCb color space
  • Rendering directly onto video
  • Blending onto a video frame
• Using live video as a texture
  • Setting up the video path
  • Creating the digital media pbuffer
  • Creating the buffer pool
  • Getting the video frame
  • Loading the video frame as texture

Time and Synchronization on SGI Machines

• Introduction to UST and UST/MSC
  • How to synchronize audio, video, graphics, MIDI, serial and other signals.
• Why Use UST?
  • Why a simple best-effort synchronization approach doesn't work so well.
• UST/MSC: Using the Frontier MSC to Detect Errors
  • Details on how to detect dropped input data and output glitches.
• Synchronization Across Machines
  • Tricks to relate the UST clock of two different machines.
• UST and Graphics
  • Ways to get UST from OpenGL and IRIS GL
• Slides from 1997 SGI Developer's Forum UST and UST/MSC Talk
  • Showcase format

Case Study: Uncompressed Video Disk I/O

• Uncompressed Video Disk I/O: Introduction and Scope
  • full-rate, full-size uncompressed video disk i/o defined
  • which SGI platforms and video devices we cover
• Concepts and Terminology for Disks and Filesystems
  • disk, disk array, disk enclosure, disk vault
  • partition
  • XLV
    • volume element, multipartition volume element, striped volume element
    • stripe unit
    • plex, concatenated plex
    • logical subvolumes: log, data, and real-time
    • logical volume
  • filesystem
  • device file, raw device file
  • XFS
    • internal vs. external log
    • filesystem sections: log, data, and real-time
• Hardware/System Setup for Uncompressed Video I/O
  • your options for disks and disk arrays on each platform
  • tips for configuring your filesystem and kernel for best performance
• Basic Uncompressed Video I/O Code
  • simple videoport API on top of VL
  • how much memory buffering do you need?
• Software Methods for Disk I/O
  • buffered I/O
  • direct I/O: satisfying its constraints, portability concerns
  • data cache concerns
  • residency concerns
  • disk seek, disk retry, disk recal concerns
  • disk command concerns
  • optimizing command size and spacing: readv/writev
  • how I/Os map to commands: XFS, XLV, dksc, host adapter
  • exploiting parallellism: asynchronous I/O
  • disk readahead
  • disk write buffering
  • disk command tag queueing
  • missed revolutions
• Getting Raw Data in and out of the Movie Library
  • how to read and write video efficiently using the QuickTime file format
  • organization of a QuickTime file
  • basic information on SGI Movie Library calls to do this

Hints for Direct Sony-Style RS-422 Deck Control

• Direct Sony-Style RS-422 Deck Control: Introduction and Scope
  • which SGI platforms and video devices we cover
  • field-accurate direct RS-422 deck control defined
• Getting 422 in and out of Your SGI
  • how to get your SGI to produce RS-422 levels
• IRIX 6.3 O2 422 Deck Control Sample Code
  • complete sample code
  • Makefile deck/Makefile
  • support file deck/simpledigits.h
  • uses tserialio, IRIX 6.3 timestamped serial I/O facility
  • uncompressed video capture and laydown with 422-style deck control
• Deck Control If You Have Real-Time Scheduling
  • hints and strategies
  • applicable on REACT/Pro or older sysmp(MP_MUSTRUN) systems

Related Non-video Topics

• Copying Data Quickly
  • Tips and pitfalls for bcopy(), memcpy(), and your code.
• Memory System Performance
  • Benchmarks for memory access
  • Read, write, and copy
  • O2, Octane, Onyx2