ENCODE\/DECODE

T&F

When we discuss “encode” in media, it often contains two parts, video encoding and audio encoding.

Video encoding is one of those important steps in a video that will determine whether the image output looks good or bad. The technical

term for this process is “encoding” but is often referred to as “conversion”.

Not all video is the same. Digital video can exist as any number of formats, using any numbers of settings. When a digital video file does not meet the specifications, or the file type is bad for the intended use, it must be converted to the proper format, using video encoder hardware or software.

The word “format” is used for many things in video, but it tends to confuse people for this very reason. So let us clarify some definitions real quick;

Video format: this includes file types, like MPEG-1(MPG), MPEG-2

(MPG),Quicktime(QT),RealMedia(RM,RMVB),Windows Media(WMV),

H.264(MP4),Divx and Xvid(AVI),FlashVideo(FLV),ect.

Playback format: This refers to final product used when viewing the video. Examples include DVD-video (DVD), VideoCD (VCD), streaming video (Youtube,Flash)

Video Specifications: For example, DVD-Video specification uses MPEG-1 or MPEG-2 with certain resolutions and settings only any old

MPEG-1 or MPEG-2 will not suffice.

When encoding video, you must consider (1) the original source and capture methods, (2) any later encodes that performed, (3) the intend output. Only by analyzing those aspects, and then considering

all the options, can a high quality encode be performed. Converting video properly is not s simply a matter of pressing the “GO” button in

an encoder program.

The Encoding class names the specific type of data representation used for an audio stream. The encoding includes aspects of the sound format other than the number of channels, sample rate, sample size, frame rate, frame size, and bite rate, audio codec.

Like video codec, audio codec are algorithms by which an audio stream is encoded. Like video codec, there are lossy and lossless audio codec.

There are lots of audio codecs: MPEG-1 Audio Layer 3 ,Advanced Audio Coding ,Windows Media Audio, Vorbis ,Dolby Digital ,Digital Theater System. One concept that audio has that video does not is channels. We’re sending sound to your speakers, right? Well, how many speakers do you have? If you’re sitting at your computer, you may only have two: one on the left and one on the right. My desktop has three: left, right, and one more on the floor. So-called “surround sound” systems can have six or more speakers, strategically placed around the room. Each speaker is fed a particular channel of the original recording. The theory is that you can sit in the middle of the six speakers, literally surrounded by six separate channels of sound, and your brain synthesizes them and feels like you’re in the middle of the action. Does it work? A multi-billion-dollar industry seems to think so. Most general-purpose audio codecs can handle two channels of sound. During recording, the sound is split into left and right channels; during encoding, both channels are stored in the same audio stream; during decoding, both channels are decoded and each is sent to the appropriate speaker. Some audio codecs can handle more than two channels, and they keep track of which channel is which and so your player can send the right sound to the right speaker.