Knowledge Base
What are audio
and video codec?
A video or audio Codec (Compression/DeCompression) is a software component allowing to encode data to be stored on a media (CD, DVD, etc...) and/ to decode it to be visualized or heard. There are also so-called "hard" codec usually embedded to camcorders or digital video players or professional and semi-professional video cards for video editing and composing.
AVI is short for "Audio Video Interleave", the original Microsoft file format for Microsoft's Video for Windows standard. It is an audio video standard designed by Microsoft and is apparently proprietary and Microsoft Windows specific. It is a format developed for storing video and audio information. Files in this format have an .AVI extension. However, Video for Windows does not require any special hardware, making it the lowest common denominator for multimedia applications.
MPEG gives excellent compression with little loss in quality of the video. MPEG support three types of data - video, audio and streaming. There are a number of standards: among them there are two flavors of MPEG available today. MPEG-1 was designed to provide VHS video quality and CD audio quality at a combined data rate of 150 kilobytes per second. MPEG-1 is displayed at 30 frames per second in a frame that is 352x240 (horizontal x vertical) pixels in size. This allows relatively high quality video images to be stored in relatively small file sizes for playback across computer networks or CD-ROM delivery. MPEG-2 is the other side of the compression coin. It is a broadcast standard specifying a playback size of 720 x 480 pixels at 60 fields per second. Data rates can range from 2 to 10 megabits per second. This means large file sizes and data rates that require specialized hardware for playback. MPEG-2 is one of the core compression technologies for DVD. See the MPEG site for more information.
This is Microsoft's new standard for audio and video which is closely tied with the Windows Operating System. The player is able to play Windows Media Video (.wmv) and Advanced Streaming Format (.asf) files, and also other formats such as QuickTime, AVI, MPEG and MP3. See the Windows Media site for more information.
RealMedia provides one of the oldest and most widespread (85% of all web-accessing computers have RealPlayer installed) Web delivery formats. The RealMedia files (.rm) can be viewed using RealPlayer 3 and above. For more information see the RealNetworks site and their user information site.
MOV is a file extension for QuickTime Video Clip. QuickTime is a video and animation system developed by Apple Computer. QuickTime is built into the Macintosh operating system and is used by most Mac applications that include video or animation. PCs can also run files in QuickTime format, but they require a special QuickTime driver. QuickTime supports most encoding formats, including Cinepak, JPEG, and MPEG. QuickTime is competing with a number of other standards, including AVI and ActiveMovie. For more information see the Apple site and their Support page.
Bitrate very often used when speaking of video or audio quality
and file size -- defines how much physical space one second of audio
or video takes in bits (note: not in bytes). The higher the bitrate,
the more times per second the original sound is sampled, thus yielding
a more faithful reproduction and better sound. When choosing an
MP3, weigh the advantage of a higher bitrate against the size of
the file. Generally speaking, a bitrate of 128 kbps or higher will
provide satisfactory sound quality.
Constant Bit Rate (CBR) encoding maintains the same bitrate throughout
an encoded file.
Variable Bit Rate (VBR) is an MP3 encoding method that's used when
file size is not an issue. Unfortunately Magic Video Converter decodes
VBR but doesn't encode it.
Selecting the proper bit rate for your projects depends on the playback
target: if you're making a VCD for playback on a DVD player, the
video must be exactly 1150 Kbps and the audio 224 Kbps.
What is DTMF in
audio converter?
Dual-tone multi-frequency (DTMF) signaling is used for telephone signaling over the line in the voice-frequency band to the call switching center. The version of DTMF used for telephone tone dialing is known by the trademarked term Touch-Tone (canceled March 13, 1984), and is standardized by ITU-T Recommendation Q.23. It is also known in the UK as MF4. Other multi-frequency systems are used for signaling internal to the telephone network.
What is Fade
In / Fade Out in audio converter?
Fade In is an effect that changes level over time increasing
in amplitude from silence.
Fade Out is an effect that changes audio level over time
falling gradually to silence. Expander is a device or computer
algorithm that reduces the level of a signal when it falls
below a specified threshold in order to exaggerate its dynamic
range.
In basic terms, a video can be thought of as being made up of numerous
snapshots, called frames. Frame Rate defines how many pictures eg.
frames one second of video or audio contains, normally used acronym
for framerate is fps - frames per second. Human eye can't see picture
changes after the framerate is more than ~24fps.
Video files with higher frame rates show motion better but have
larger file sizes. Typical frame rates are 29.97 for NTSC video
(in American TV system), 25 for PAL (European system) video, and
24 for film. When exporting low-bandwidth versions, select a frame
rate that is 1/2, 1/3, or 1/4 of the original frame rate. Setting
a frame rate higher than the original frame rate will make the file
larger but will not improve the quality.
Note that MPEG format only supports 23.976, 24, 25, 29.97, 30 frame
rates.
Variable bit rate (VBR) encoding is an alternative to constant bit
rate encoding and is supported by some codecs. Where CBR encoding
strives to maintain the bit rate of the encoded media, VBR strives
to achieve the best possible quality of the encoded media.
The quality of encoded content is determined by the amount of data
that is lost when the content is compressed and decompressed. Many
factors affect the loss of data in the compression process, but
in general, the more complex the original data and the higher the
compression ratio, the more detail is lost in the compression process.
Flanger is an audio effect that occurs when two identical signals are mixed together, but with one signal time-delayed by a small and gradually changing amount, usually smaller than 20 milliseconds. This produces a swept comb filter effect: peaks and notches are produced in the resultant frequency spectrum, related to each other in a linear harmonic series. Varying the time delay causes these to sweep up and down the frequency spectrum. Part of the output signal is usually fed back to the input (a "re-circulating delay line"), producing a resonance effect which further enhances the intensity of the peaks and troughs. The phase of the fed-back signal is sometimes inverted, producing another variation on the flanging sound.
Windows Media Format is a proprietary format designed primarily
for streaming audio, video and text from Internet servers to client
computers. A Windows Media file can also be stored and played locally.
Each Windows Media file contains one or more media streams that
together form a multimedia presentation. Stream delivery is synchronized
to a common timeline. The following list presents the key features
of Windows Media Format:
A Windows Media file can be transported over any underlying data
communication transport protocol. Windows Media Format does not
specify the format of data packets for different network protocols.
Windows Media Format is scalable to any bandwidth. A single input
stream can be encoded into multiple output streams within a single
Windows Media file. Each scaled stream differs by the bit rate at
which it can be rendered, and only one can be rendered at a time.
The Windows Media server uses intelligent streaming to send the
highest quality stream a client is capable of receiving.
The delivery and presentation of multiple media streams is synchronized
to a common timeline. The media data inside a Windows Media file
is time-stamped.
A Windows Media file can contain one video, one audio and one script
stream.
A client does not need to store Windows Media-based content to play
a multimedia stream.
Sound files are created by taking "samples" or snapshots of sound waves. As the sampling rate increases, more samples are taken in a given time interval. The higher the "sampling rate", the better the quality of the sound.