Video Film Production

1
Video / Film Production

• Dr. Gino Cheng
• Hong Kong University of Science and Technology
• eegino_at_ust.hk, 2358-8540

2
Video vs. Photography

• Images extracted from CCD
• Limited dynamic range
• Scan rate issues (video of TV)
• Temporal issues (e.g., motion continuity)
• Stabilization

3
Video Camera

• Variety of video formats
• New digital formats
• Digital effects
• Stabilization
• Titling and transitions
• White balance
• Set reference white color

4
Typical Set-up
Actor
Camera man
Sound
Grip(s)
5
Two Styles of Shooting

• TV style production
• TV Sitcoms
• Football/basketball
• Film style production
• Movies

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TV Style Production
Camera men
Director
Actors
Switcher
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Film Style Production

• Pre-production
• Script
• Breakdown
• Design
• Scheduling
• Production
• On-location shots
• Post-production
• Editing
• Sound design, music

8
Planning and Production

• Complex design process
• Analogous to VLSI design
• Currently all of the data is on paper and in
  peoples heads
• Limited/primitive tools
• Lots of opportunities for digital media in
  preproduction/production
• Production and planning for new media is an open
  area

9
Roles

• Producer - gets the money
• Director - supervises the production has final
  say on all creative decisions.
• Director of photography - works with camera and
  lighting
• Art director - designs props, sets, props
• Actors - play roles
• Composer - creates music
• Sound designer - sound effects, foley

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Production Output

• Film
• High resolution scan (250mb/frame)
• Color matching most important
• Scan -gt monitor -gt print
• Video
• Digital Betacam, Betacam
• DV Cam
• Hi8 / Svideo
• VHS, 8

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Production Output

• Computer
• MPEG 2
• MPEG 1
• H.263/H.261
• AVI / Quicktime proprietary compression formats
• Cinepak
• Indeo
• Real-video

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Digital Video

• Capture at highest quality possible
• Storage is a factor (10MB/sec)
• Bandwidth to HD
• Processing (hardware support)
• Try at lab
• Have set-up for experimenting
• Lab machines have JAZ drives

13
Video Basics

• Video signal
• NTSC, PAL
• RGB - (3 wire)
• Y, C - (2 wire)
• Composite - (one wire)

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Composite Video

• Interlaced 30 frames per second, two fields per
  frame
• Interlace relaxes scanning rate requirement
• Compatible with black and white
• Color information modulated onto black and white
  signal

15
Digital Video

• Big move towards digital video in the US - why?
• Progressive scan (not interlaced)
• Early video capture grabbed fields rather than
  frames
• Typically 14.3MB/sec required for NTSC
• Quality generally bandwidth/storage limited
• Variety of formats for applications

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Digital Video Formats

• CCIR 601 (1982) - Early digital tape format
• 720x486x30 frames per second
• Color sub-sampled at 422
• CIF
• 352x240x30 frames per second
• QCIF (Quarter CIF)
• Video conferencing

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Emerging Format - DVCam

• Digital tape format
• Sub-samples color differently (poorer color)
• Cheap cam-corder/home digital format
• Intraframe compression (JPEG) for 5-1 reduction
• No drop-out (as with Hi8)
• TV production / documentaries using this format
• Direct to HD transfer with Firewire

18
Video Compression

• Basic idea
• Use intraframe compression to compress frames
  (e.g., JPEG)
• Difference between one frame and the next isnt
  too great
• Only send information that isnt in the new frame
• Difference
• Offset (use previous frame as a look-up table)

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H.261

• JPEG frames (I frame)
• Only differences between the previous frame and
  the next frame (P frame)
• Motion vectors describe blocks that are offset
  from the previous frame
• Can vary the quantization for intraframe
  compression
• Why would you want to vary the quantization?

20
H.261

• Structure
• Picture
• Group-of-blocks
• Macroblock
• Block
• Group of blocks good for compression, error
  recovery
• Can quantize at GOB, Macroblock, or block -
  inheritance

21
MPEG 1

• Developed for VCD (1.5mbits/sec)
• Standard has three parts
• Video based on H.261 and JPEG
• Audio perceptual coding
• System control interleaving of streams
• Introduces B-frames
• B frames based upon previous and future frame
• Pain in the butt for editing

22
MPEG Differences with H.261

• Larger gaps between I and P frames (lots of B
  frames in between) so expand motion vector search
• Vectors specified by fraction of pixel
• Use slice rather than group of blocks

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MPEG Video
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Video Bitstream
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Bitstream

• Sequence Information
• Video Params include width, height, aspect ratio
  of pixels, picture rate.
• Bitstream Params are bit rate, buffer size, and
  constrained parameters flag (means bitstream can
  be decoded by most hardware)
• Two types of QTs one for intra-coded blocks
  (I-frames) and one for inter-coded blocks
  (P-frames).

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Bitstream

• Group of Pictures (GOP) information
• Time code bit field with SMPTE time code (hours,
  minutes, seconds, frame).
• GOP Params are bits describing structure of GOP.
  Is GOP closed? Does it have a dangling pointer
  broken?
• Picture Information
• Type I, P, or B-frame?
• Buffer Params indicate how full decoders buffer
  should be before starting decode.
• Encode Params indicate whether half pixel motion
  vectors are used.

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Bitstream

• Slice information
• Vert Pos what line does this slice start on?
• QScale How is the quantization table scaled in
  this slice?
• Macroblock information
• Addr Incr number of MBs to skip.
• Type Does this MB use a motion vector? What
  type?
• QScale How is the quantization table scaled in
  this MB?
• Coded Block Pattern (CBP) bitmap indicating
  which blocks are coded.

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Software Decode

• Software Decoder goals portable, multiple
  display types
• Initial measurements (320x240, sparc 1) about
  2.7 sec/frame

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MPEG Encoding

• Computationally intensive - how to determine best
  I and P frames
• Motion vector search - how to encode P and B
  blocks
• Hierarchical methods
• Use history information (track motion of blocks)

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MPEG 2

• Structurally similar to MPEG 1, but support for a
  variety of formats (including HDTV)
• Supports interlace (blocks based upon fields
  rather than frames)
• Better color (444)
• More bandwidth required
• DVD

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Audio

• Interleaved with video and buffered for playback
  (e.g., 1/2 second of video, 1/2 second of audio,
  etc.)
• Perceptual coding, 3 layers (or formats)

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MPEG 4

• Emerging format for low-bitrate and interactive
• Video segmented into objects that are composited
  at the player
• Can combine static backgrounds, video, and 3D
  objects (e.g., VRML like models)
• Modular architecture to support future coding
  techniques
• Example

33
MPEG 7

• Not a video format, but a standard for describing
  video content
• Challenge of content indexed databases
• Still under development
• Check out mpeg

34
H.263

• Video conferencing
• SQCIF (128x96 pixels)
• Similar to MPEG
• 1/2 pixel resolution
• B-frames
• Expanded motion vector search

35
Video Programming

• Quicktime
• Synchronous presentation (video, audio, MIDI,
  data, etc.)
• AVI
• Video only
• Programming APIs
• Visual C - Activemovie
• Java - Intels Media Framework