Midterm Exam Multimedia
Midterm Exam Multimedia
Midterm Exam Multimedia
Graduate School
MIDTERM EXAM
MSIT 215-Multimedia
GRACELY J. CARSON
Instruction.
I. Provide an example of any multimedia application that uses a lossy and
lossless compression. From your given example, show the process on how it
is compressed.
>> The MP3 format is one that uses lossy compression. This means that it
loses some of the audio information found in the original to make the
compressed file much smaller. The information that lossy compression loses
is the information deemed least important to the file. In music, this tends to be
the very high and very low frequencies that are not considered to add as
much to the music as the range of frequencies in between.
>> Briefly, heres how MP3 (and most other compression schemes)
work. The process employs a combination of digital technology and the
science of aural perception (psychoacoustics) to remove data bits from the
original digital file that are considered to be essentially inaudible. These
bits can include frequencies beyond the normal threshold of human
hearing, sounds that are masked by other sounds, and various other
redundant sonic information.
The point of contention with this whole concept is just how much of that
data is truly inaudible. While some bits can be removed with little
consequence, much of what gets stripped away can subtly affect our
perception of how things sound. While moderately compressed files can
deliver near-CD quality sound, too much compression can remove elusive
qualities that can make a difference to how we perceive music on a
subconscious level.
With any compression, some audio quality loss is inevitable. Very high
frequencies are typically the first data to be eliminated, and while in theory
these sounds are inaudible, their loss can rob your music of its subtle
overtones, presence, dynamic range and depth of field.
The audio resolution and sonic quality of an MP3 is determined by the
bit rate at which its encoded. The higher the bitrate, the more data per
second of music. As youd expect, a higher bitrate creates better quality
audio, along with a larger file.
Generally speaking, 128 kbps (kilobits per second) is considered the
bit rate at which an MP3 begins to exhibit artifacts of data compression.
Not coincidently, its also the rate many websites use for downloads, since
it offers a smaller file size with relatively minimal loss. Rates below 128
kbps are usually not recommended for anything other than spoken word
recordings. Bitrates of 192 kbps, 256 kbps, or higher preserve most of the
original sonic information, making them a better bet for music you care
about.
Another alternative is to encode using a VBR, or variable bit rate. VBR
examines the data as its encoding, using a lower rate for simple passages
and a higher rate for more complex ones. While the resulting file size is
smaller than using a higher bitrate, sometimes VBR encoding can end up
compromising the audio fidelity of delicate material like a solo acoustic
guitar or vocal.
>> WAV files don't involve any compression at all and will be the size of files
that you have calculated already. There are lossless compressed file formats
out there such as FLAC which compress the WAV file into data generally 50%
the original size. To do this it uses run length encoding, which looks for
repeated patterns in the sound file, and instead of recording each pattern
separately, it stores information on how many times the pattern occurs in a
row. Let us take a hypothetical set of sample points:
00000000000000000000012345432100000000000000000123456787656789
876
As you can see the silent area takes up a large part of the file, instead of
recording these individually we can set data to state how many silent samples
there are in a row, massively reducing the file size:
(21-0)123454321(17-0)123456787656789876
Possible Queries
Video Query:
Police officer Rocky is examining a surveillance video of a
particular person being fatally assaulted by an assailant. However,
the assailant's face is occluded and image processing algorithms
return very poor matches. Rocky thinks the assault was by
someone known to the victim.
Query: Find all video segments in which the victim of the assault
appears.
By examining the answer of the above query, Rocky hopes to find
other people who have previously interacted with the victim.