Analog VDO• Motion VDO was originally created and stored in analog form.
Digital VDO• A means of reproducing the continuous VDO waveform as a stream of digital numbers. to va rious t: im mune analogB eneﬁ ttributed todi stor tion a ise ... such as n o
open wiki to Interlacing embrace the explanation!!• Interlacing was originally conceived as a way to achieve good visual quality within a limitations of a narrow bandwidth. odd ﬁeld even ﬁeld
Progressive Scanning (non-interlaced scanning)• A method of representing moving images on a display screen, in which every pixel is represented in each frame.• Computer monitors use a progressive scan.• The standard refresh rate for a ﬂicker-free display is a vertical scan rate of 75 Hz or higher.• It’s used to project movies in theaters.
Notein digital TV terminology: interlaced scan is denoted by a lowercase i progressive scan is denoted by a lowercase p frame rate: (60i, 24p) resolution: (1080i, 720p)
Frame Rate• Frame frequency is a measure of how quickly an image device can produce unique consecutive images called frames. (expressed in frames per second - fps)• Typically, the human eye can interpret motion at 10 fps, but this rate causes a ﬂicker effect that’s distract.• Increasing the frame rate reduces ﬂickering.
Frame Rate• Movies - 14 fps• Television: • NTSC - 29.97 fps • HDTV - 60 fps• VDO games (frame rate is very important): • action-oriented games - 20-30 fps • 3D-heavy games - 90-100 fps
Aspect Ratios• The ratio of the width of the image to its height (w:h) • motion-picture - 1.85:1 and 2.35:1 • tv screens - 1.33:1 (aka 4:3) • HDTV - 1.78:1 (aka 16:9) 16:9 4:3 letterbox
Compression• VDO is huge - one sec of analog VDO stored in an uncompressed digital format takes up 1 MB of disk space • thus, 5-min VDO ~ 300 MB • not practical• VDO compression is a MUST • VDO contains many spatial and temporal redundancies • Codecs are needed for creating and viewing
VDO Compression• Spatial compression (intra-frame)• Temporal compression (inter-frame)• Video compression is a tradeoff between disk space, video quality, and the cost of hardware required to decompress the video in a reasonable time.
Spatial Compression• Just image compression applied to a sequence of images.
Temporal Compression• Make key frames, say every 6 frames and do the spatial compression on these frames.• Between key frames, each one of them will be replaced by a difference frame.
AVI• Most common AV data on Windows• Can be saved in a variety of compression schemes - full frames (uncompressed), Radius’s Cinepak, Intel Video, and Indeo.
MOV• Quicktime Movie was developed by Apple Computer• MPEG-4• Qt 7 (and later) use H.264
MPG• The compressed VDO ﬁle format for standard DVD using the MPEG-2 encoding standard• A large ﬁle can be transferred to MPEG with little loss of quality while dropping the bit rate a great deal
• The MPEG group develops the standards for encoding VDO and audio• MPEG standards: • MPEG-1: used as VCD standard (MP3 is the popular compression) • MPEG-2: use in many things such as DVD, digital satellite TV and so on • MPEG-4: support 3D content, low bit-rate encoding, support for Digital Right Management
Others• WMV • a part of Windows Media framework • used for streaming VDO over the internet • uses MPEG-4 standard• RM • a multimedia container with RealVideo and RealAudio codecs in a single ﬁle • is used to stream AV over the internet
Coaxial• VDO and audio signals are both carries in one cable• Poorest transfer
A/V• Use RCA connectors• Yellow is (composite) video• Red is right audio & White is left audio
S-Video• Separate video - transmit VDO signals over a cable by dividing the VDO info into 2 separate signals: color (chrominance) and brightness (luminance)• Sharper than composite VDO• must be used in conjunction with audio cables
FireWire• Developed by Apple Computer• IEEE-1394 standard• 400 Mbps• higher transfer rates are available (800, 1600, and up to 3100 Mbps)
Transferring fromRecorder to Computer• Calculate disk space (uncompressed): • (pixel width) x (pixel height) x (color bit depth) x (fps) x (duration in secs) / 8,000,000• say, 3-min VDO @ 15 fps, 24-bit depth, 320x240 pixels will take: • (320) x (240) x (24) x (15) x (180) / 8,000,000 = 622 MB
VDO Editing• Editing: • cut and paste sections • add special effects • add transitions • add titles