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Compression standards for video

Motion JPEG

With motion JPEG, each frame within the video is

stored as a complete image in the JPEG format. The still

images are displayed at a high frame rate to produce

very high-quality video, but at the cost of producing

comparatively large ﬁ le sizes.

H.261, 263, 321, 324 etc.

These refer to the standards recommended by the Inter-

national Telecommunications Union (ITU). Designed

for video conferencing, but sometimes used for net-

work cameras, these standards offer a high frame rate.

However, they produce a very low image quality, usu-

ally with image resolutions up to 352x288 pixels. As

the available resolution is quite limiting, newer pro-

ducts tend not to use this standard.

MPEG 1

Moving Picture Encoding Group international standard

ISO/IEC 11172.

There are numerous possible variations of this

format, but normally the Constraint Parameters Bit-

stream, CPB standard is used, giving ‘VCR quality’. This

gives a performance of up to 352x288 pixel, 30 fps,

max 1.86 Mbit/s.

Audio according to MPEG 1 layer 1, 2 and 3 are

included in the standard. (MPEG 1 layer 3 audio is

often called MP3.)

Video CDs use the MPEG 1 format at a bit rate of 1.2

Mbit/s.

As the available resolution is quite limiting, newer

products tend to use MPEG 2 instead.

MPEG 2

Moving Picture Encoding Group international standard

ISO/IEC 13818. A popular standard that offers high-

quality video suitable for installations where TV-qua-

lity is needed. There are numerous possible variations

of this format but normally the Main Proﬁ le at Main

Level, MP@ML standard is used to provide a resolution

of 720x480 pixels at 30 fps (NTSC) or 720x576, 25 fps

(PAL). The bit rate is typically 1-10 Mbit/s. An MPEG 2

player can display either MPEG 1 or MPEG 2 formats.

Audio conforming to AC3, AAC and MPEG 1 layer

1, 2, 3 standards are included in this format. (MPEG-1

layer 3 audio is often called MP3.)

DVD-ﬁ lms and digital cable TV use MPEG 2 with a

bit rate of approx. 5 Mbit/s.

MPEG 3

A cancelled standard aimed at HDTV (High Deﬁ nition TV).

MPEG 4

Moving Picture Encoding Group international standard

ISO/IEC 14496. This standard covers a wide variety of

applications ranging from the video displayed in cel-

lular phones, to full feature-length movies shown in a

cinema. MPEG 4 is widely tipped to be the video stan-

dard of the future but it is still relatively new and not

widely used.

This format contains many enhancements to any of

the early MPEG standards; for example, it offers nar-

rower bandwidth and can mix video with text, graphics

and 2-D and 3-D animation layers. Although these new

enhancements pack the video in a very efﬁ cient manner,

a lot of computing power is needed to use them in real

time. It therefore requires a substantial capital investment

in more powerful computers.

Compressed using JPEG Compressed using H.261

The image of a moving person will become like a mosaic if H-series compression is used. The normally uninteresting background will however retain its good and

clear image quality.

I MAGE QUALITY

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Axis 2400+ Manuale Utente Pagina 35

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