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Multimedia 1033 > Week 9 and 10 > Flashcards

Week 9 and 10 Flashcards

1
Q

what is a video

A

a sequence of still images (photographs) that create the illusion of movement when played in succession

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2
Q

what is each still image called

A

a frame

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3
Q

movies on film played from ___ to ___ fps

A

24-30

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4
Q

tv was originally ___fps

A

29.97

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5
Q

computer displays video at at least ___fps

A

12-15

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6
Q

in digital video, each frame is a ___ graphic stored as 0 and 1

A

bitmapped

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7
Q

describe the sampling and quantization processes of film

A

sampling = each frame sampled into a discrete sample and each sample becomes a pixel
quantization process = assigning a value to each colour

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8
Q

what can we “sample” with MOTION

A
  • Timing of the motion
  • Sampling = frames
  • Higher FPS = more accurate motion but a larger file size
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9
Q

still images use rgb but videos use

A

YUV (YIQ) or YCbCr for MPEG compression

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10
Q

what does the Y and UV in YUV stand for

A 
Y = luminance Brightness
UV = CbCr in YCbCr = chrominance (colour or hue)
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11
Q

black and white tv only used which part of YUV

A

Y because it had no chrominance (colour)

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12
Q

when we went from black and white to colour TV, we had to lose ___ because colour increased the file size of each frame

A

fps

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13
Q

the human eye can detect changes in ____ more easily than changes in __

A

brightness than colour

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14
Q

it is common for the ____ to be sampled less often because ___

A

chroma sample (UV) changes in colour are less noticeable

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15
Q

what is the format of colour sampling method

A

Y:U:V
u and v are colour hue
y is brightness
4:4:4 is no compression

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16
Q

4:4:4 colour sampling is how much compression

A

none

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17
Q

4:2:2 colour sampling is how much compression

A

33% on hue, reduced from 12 samples to 8

4:2:2 subsample rate means that out of four colours, two of them will disregard their own colour and take the colour of their adjacent pixel

  • lose information
  • and save space in your media
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18
Q

4:2:0 colour sampling is how much compression

A

50% on hue, reduced from 12 samples to 6

4:2:0 subsample rate means that 3 out of four colours will disregard their own colour and take the colour of the last one to save a lot of space in the end

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19
Q

if you want to compress colour, you ….

A

keep the brightness but take the averages of the colours

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20
Q

what kind of display did original tvs have

A

Interlaced display

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21
Q

what is interlaced display

A

uses 48 horizonal scan lines, our eyes see phosphor dots on the screen and an electron beam excites the dots and gun scans through the dots horizontally
only scans every other line odd and starts back up at the top and draws the even lines
- takes two passes, one pass= feild

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22
Q

what is a complete scan in interlaced display

A

starts at top left and scans each row until bottom right

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23
Q

each pass in an interlaced display is called a

A

field

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24
Q

what is a progressive display

A

what we use instead of interlacing

means the whole image is shown at once instead of displaying in passes

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25
Q

480i means

A

interlaced is i and 480 is the number of feilds

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26
Q

720p and 1080p mean

A 
progressive= p
means the whole image is shown at onced
720p is 1280x720 (720 indicates number of rows)
1080p is 1920x1080
number indicates number of pixels
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27
Q

4K compared to 480i, 720p, and 1080p
whats the difference
what is the resolution of 4k and 8k

A

for 480i, 720p and 1080p, look at horizontal rows but for 4k and 8k you look at vertical columns
7680x4320 - 8k
3840x2160 - 4k

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28
Q

what do TV specs mean -

A

the tv specifications.
The 50” means 50 diagonal inches (not sure
why it is not metric  )
 The 4K or 1080 or 720 means number of
pixels
◦ Originally TVs before 1980s had 480 horizontal scan
lines
◦ Then HD TVs had either 1080 or 720 horizontal
scan lines
◦ NOW 4K or 8K TVs have ~4000 or 8000
VERTICAL scan lines
 You may see i or p – interlaced or progressive

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29
Q

what does 4k refer to

A

width

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30
Q

high definition resolutions started at __ and then went up to ___, ___ and finally ___

A

720, 1080, 1440 then 4K

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31
Q

apple suggests that small devices should be held at ___ inches away from your face and that the screen resolution should be at least ___ ppi

A

10-12, 300 ppi

at 300 ppi, pixels are so close together and that at 10-12 inches from your eye, things start to look like continuous curves
this is refered to as high retina display

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32
Q

what is high retina display

A

Apple suggests that small devices (iPads etc.) should be held at 10-12 inches away from you face and that the screen resolution should be at least 300 ppi to look crisp.

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33
Q

Retina Displays have a pixel density high enough so that your eyes cant detect pixels at a normal viewing distance.
for this you must consider

A
  • pixel density
    viewing distance
    display size
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34
Q

what are some things to things to think about before exporting a video

A

where will i be putting my video
- on the web, dvd video etc
who is my audience
will i still need to edit it later on or can i compress it all

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35
Q

why should you compress a video

A

they are fucking long

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36
Q

what is bit rate / data rate

A

amount of video processed per second

Bit rate = amount of data used to encode video or audio - megabits per second (Mbps) kilobits per second(kbps)

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37
Q

how do you calculate bit rate average

A

average bit rate = file size/length in seconds of video

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38
Q

bit rate is normally measured in

A

bits not bytes

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39
Q

don’t just consider the file size of the video, also consider how many bits you have to get across in a given amount of time

A

think about file size as water in pool
think about bandwidth as hose to fil pool
think of pressure as bitrate (filesize/length in seconds)

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40
Q

how to compress a video: 2 ways

A

take each image/frame and compress each frame individually
take all frames together and see if there are any spots where its not really changing … you can store that info in a single frame

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41
Q

compression strategies

A

lower frame size of vid
lower frame rate of video (removing frames or adding seconds)
pick a codec that does higher compression
lower picture quality of video
lower colour depth
play with the audio but this probably wont do much

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42
Q

what is a codec

A

is a piece of code that compresses a video or audio as it is created (exported from the editing software) and then when displaying it to the user decompresses the video or audio (also stands for the coder/decoder)

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43
Q

what codec does youtube use

A

H.264

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44
Q

examples of codex

A

DivX and H.264

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45
Q

if you get a vid on your machine and cant play it, what does this probably mean

A

that youre computer is missing the appropriate codec

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46
Q

compression concepts- spacial vs temporal

A

spatial compresses each frame individually and uses same compression technique as JPG, codecs that do spatial compression are animation, planarRGB
temporal compression does better compression but is not good for sports games because it saves info on specified key framesand the other frames just save differences from frame to frame

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47
Q

what is temporal compression - video

A

better compression
good for talkshow not for action games

  • Save info on selected frames (called keyframes)
  • all the other frames just save the differences from the previous keyframe
  • good when the difference between current frame an keyframe is small
  • codecs that use temporal compression: Sorenson video, H.264
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48
Q

spatial compression - video

A

Spatial

  • Compresses each frame individually
  • uses the same techniques as JPG compression
  • Codecs that do spatial compression are Animation, planarRGB
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49
Q

lossy vs lossless compression in video

A

lossy lowers video quality but gets better file size and better data/bit rate (filesize/length)

lossless looks for large blocks of pixels that are the same to do Run length encoding

Lossy vs lossless depends on the codec

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50
Q

what does bit rate affect

A
  • file size and quality of video
  • accessibility of file (how fast the internet connection needs to be to access it)
  • how costly it is to upload the video on your own site
51
Q

how to insert video in HTML

A
52
Q

what three video formats does html5 support

A
  • MP4
  • WebM
  • Ogg
  • will NOT allow .avi
53
Q

what vid format does html5 not support

A

.avi

.flv

54
Q

apple will not support what video format

A

.flv

55
Q 
If a TV has a colour sampling method 4:2:2, the number 4 represents the:
 A. amount of compression
 B. amount of colour
 C. brightness
 D. colour bit depth
A

c

56
Q

Older TVs displayed frames over two passes, showing alternating lines and then going back to fill in those gaps. This process is called ___.

A

interlacing

57
Q

Apple suggests that handheld devices should be held at 5-6 inches away from your face.

A

no its 10-12in away from a 300ppi device

58
Q

When calculating the file size of a video, one of the biggest factors in increased sizes is the audio component.
True
False

A

false

59
Q

Calculate the bit rate of a video that has a file size of 200Mb and that is 25 seconds long. Bit rate = _ Mbps.

A

8

60
Q

H.264 is one of the most common codecs and is used by YouTube.
True
False

A

true

61
Q 
One video compression strategy is to reduce the frame rate and the number of frames. For which of the following filmed events would this approach be most suitable?
 A. Hockey game
 B. Tennis match
 C. Poker tournament
 D. Nascar racing
A

c

62
Q

When embedding a video into a webpage with HTML5, what is the meaning of the #t=5,30 as shown below?

A. It tells the browser to compress the video so that the file size is in the range of 5-30 MB.
B. It tells the browser that the video is 5MB in size and 30 seconds long.
C. It tells the browser to start the video at 5 seconds into the clip and stop at 30 seconds into the clip.
D. It tells the browser to start the video at 5:30 into the clip.

A

c

63
Q

ndicate which of the statements are true about downloading videos (check all that apply).
A. Downloading used to be the only option for watching videos from the Internet.
B. Downloading comes in two forms: unicast and multicast.
C. An advantage of downloading compared to streaming is that it reduces the wait times for the users.
D. Downloading makes the most sense for videos that the users intend to watch multiple times.

A

ad

64
Q

an advantage of downloading compared to streaming is that…

A

it reduces wait time for users

65
Q

The form of subtitles that is embedded in the video and cannot be turned off is called __.

A

hard

66
Q 
An audio waveform with gradual (spread apart) waves represents a \_\_\_\_\_\_\_ sound than a waveform with tight (close together) waves.
 A. more high-pitched
 B. louder
 C. more low-pitched
 D. quieter
A

c

67
Q

In a higher-pitch sound, you must take more samples than you would for a lower-pitch sound to ensure the audio is represented accurately.
True
False

A

true

68
Q 
The number of samples taken per second of audio is called the:
 A. sample depth
 B. sample rate
 C. sample size
 D. sample number
A

b

69
Q 
Indicate which of the following are strategies for reducing the filesize of an audio file (check all that apply).
 A. Changing from mono to stereo	
 B. Compressing with a codec	
 C. Decreasing the sample rate	
 D. Decreasing the sample size
A

b, c, d,

70
Q

MP3 and WAV are the two audio formats that offer the highest compression rates.
True
Fals

A

false

71
Q

MIDI files store audio with a higher sample rate than MP3 files.
True
False

A

false

72
Q

Audio files that contain people talking, without any singing or music, should be sampled at about 8000 Hertz.
True
False

A

true

73
Q

what indicates html5

A
74
Q

what is a container file format

A

a file format that stores both the data (the frames) and how to play the data ( which codec to use)
some common containers
- .avi - sometimes has uncompressed video just depends, no streaming
- .flv - doesn’t allow subtitle
- .ogg - free open source container format
- .mp4

75
Q

difference between codec and container

A

a codec is a method of encoding and deconding more data and more specifically, a protocol for compressing data

a container is reffered to as the format. it is what holds the grouping of compressed videos
is how the compressed video is stored

76
Q

two kinds of subtitles

A

hard and soft

77
Q

what is hard subtitle

A

hard (hard subs): embedded into vid file so they can not be turned off or removed

78
Q

what is a soft subtitle

A

soft (softsubs) are usually stored in a separate file telling what text to appear at what time in the video. These can be turned off/on as needed.

79
Q

for video embedded in a website with soft subtitiles, the format of the subtitles has to be a ___ file

A

.vtt

web video text tracks

80
Q

what are two ways of getting videos from the internet

A

downloading (making a copy of the file/video on ur machine)

streaming (like listening to radie but you cant save it without difficulties)

81
Q

downloading a vid to watch it used to be the only option

t/f

A

true

82
Q

how does downloading work

A
  • when you visit a website containing a video, the entire video must be downloaded to your computer before you can play it
    • progressive downloads allow you to start watching as soon as it has downloaded enough bits to stay ahead of the download
  • for the web, usually stored on a HTTP protocol
83
Q

what are advantages or disadvantages of downloading a video on your computer

A

dis: you have to wait to play video and takes up storage on computer
adv: once you get it on your computer you can play it over and over and then it saves time

84
Q

how does streaming work

A
  • when you visit a website containing a video, the entire video must be downloaded to your computer before you can play it
    • progressive downloads allow you to start watching as soon as it has downloaded enough bits to stay ahead of the download
  • for the web, usually stored on a HTTP protocol
85
Q

streaming advantages and disadvantages

A
  • no high quality vid
  • cant fast forard
  • maybe can pause and rewind
  • advantages
    • you can watch it immediately
      if the data rate (bit rate) of the encoded video file is bigger than the amount of bandwidth available, the video will frequently stop playing
86
Q

when will a streamed video stop playing

A

if the data rate (bit rate) of the encoded video file is bigger than the amount of bandwidth available, the video will frequently stop playing

87
Q

what is unicast streaming

A

each user gets his/her own stream of video, the server has to send out a lot of data if several users are watching at once
every person gets they’re own stream of the data

requires ppl sending data to use a lot of bandwidth

requires a lot more data to be sent out because each person gets their own version so they can pause etc

88
Q

what is multicast streaming

A

send the same stream to a bunch of users but then they lose the ability to pause, rewind, etc

sending out one stream of data but if one person passes it pauses for anyone

89
Q

what is adaptive streaming

A

when you can change the quality of the video

probably good to do depending on your bandwidth

90
Q

youtube converts your uploaded vid into …

A

mp4

91
Q

youtube always reencodes your video t/f

A

true

92
Q

should you redownload a vid you uploaded on youtube to edit again?

A

no because its alraedy compressed, so you dont want it to get re compressed.

93
Q
  • Going from 1080p HD video to 4Kvideo will not always improve video quality on the internet because of compression
    t/f
A

if you encode at the same bit rate ad the bitrate is low, the 1080 video will be clearer than the 4k video because it has less compression done to it.

94
Q

t/f over 75% of all videos are viewed on mobile devices t/f

A

true

95
Q

what is sound

A

pressure waves in the air

96
Q

waveform?

A

sereis of reoccurring waves

97
Q

what indicates volume of wave

A

amplitude

how tall it is

98
Q

what indicates pitch of wave in sound

A

how close together each wave is (closer = higher pitch)

99
Q

a sound wave is ____ but computers are___

A

analog

digital

100
Q

what is Nyquisit limit

A

rule that says you must take at least 2 samples for every cycle of the wave
if you take less than 2, you will get a completely different sound wave
therefore you must take more samples of higher frequency because more waves occur in the same amnt of time

101
Q

advantage of taking more samples of sound

A

you get higher quality sound, but then your file size gets big

102
Q

what is a sample rate

A

the number of samples we take per second of audio or number of times per second the waveform is measured

103
Q

sample rate of voice only

A

8000Hz or 8KHz

104
Q

AM radio sample rate

A

11.025KHz

105
Q

sample rate is measured in Hz

A

Hz

106
Q

FM Radio Quality

A

22 KHz (music

107
Q

CD quality

A

44.1 kHz

108
Q

t/f you need less quality to represent sound from voice

A

t

109
Q

what would 1-bit sampling sound look like

A

it would just have two tones two notes

110
Q

what would 2 bit sampling sound like

A 
it would have four tones
00
01
10
11
111
Q

CDs use __-bit rate

A

16-bit rate 65536 possible values could be given to each sample

112
Q

what is the disadvantage of having a higher bit rate for the sample size

A

Huge file size

113
Q

uncompressed audio is stored as

A

WAV

114
Q

How does the sound wave get converted to be stored on our computer

A

uses sound card

  • computers have a sound card which samples (sets the number of samples and quantized) the sound wave from a microphone
  • sound card has an analog-to-digital converter(ADC) for recording and a Digital-to-Analog Converter (DAC) for playing audio
  • operating system (windows, mac, linux) talks to the sound card to actually handle the recording and playback
115
Q

sound compression strategies

A

reduce number of samples (sample rate)

  • go from 44KHz to 22KHz - affects quality
  • amount of times you take a sample
  • all else staying equal, halving the num of samples will approx half the file size

reduce bit depth (sample size)

  • go from 16 bit to 8 bit - affects quality
  • aka using fewer bits to represent the sound range
  • this will also approx half file size

reduce num of channels

  • just combine where sounds comes from to unify it
  • in mono there is 1 channel
  • in stereo there are 2
  • changing from stereo to mono will 1/2 the size of the file

compress using appropriate codec

116
Q

most famous audio file format that does lossy compression

A
  • MP3!!!!
117
Q

who invented mp3

A

Karlheinz Brandenburg! he made up mp3 by removing the unnecessary background sounds that no one would notice if they were gone

can compress a song from a cd (44khz & 16 bit) to 1/11 of its size

based on the idea that some tones become unable to hear when another tone is present

118
Q

uncompressed file formats for sound

A
  • .wav (very common 44KHz, 16 bit)
  • .aiff
  • CDDA (Compact disc digital audio defined in the red book which contains audio standards - standard for CDs 44KHz 16 bit per sample, 2 channels)
    • thus 1 second of music must be laid at a bit rate of 44100161=1411200 bits per second = 1411.2 kbits per second
    • copare with mp3 - 128 kbits per second is most common, makes it good for the internet
119
Q

what does MIDI sound do and what info does it hold

A

MIDI sound deals with music and synthesized sound it does not handle voices or noise well.

  • which instrument is supposed to be represented
  • the note being played
  • how hard the note was pressed
120
Q

Question: What are the disadvantages of MIDI files?

A

Doesnt work for voice, cant incorporate into a website easily (need to convert to WAV or mp3
not all browsers will play it
also they are sometimes too perfect

121
Q

linking music to html

A

Music that doesnt start playing on webpage until user clicks on link

<p>Download a
<a>sound file </a>
</p>

have music embedded in web page

122
Q

Question: What are the advantages of MIDI files?

A

small file sizes are easy to edit and change (3 minutes)

123
Q

Before digital video,these issues when copying one video

A

Had to copy from one tape to another tape and had to load up tapes on a machine to copy
Loss of quality after each copy madr

Multimedia 1033 (5 decks)

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