>> Glossary of Terms

Since the users might experience trouble from the new terms and false knowledge, we are going to introduce you to the terms related to conversion.

 

Codec
Codec is a combination of the words Coder and Decoder, and is used to represent all the modules that compresses (Coder, Compressor, Compression) video or audio data and decompresses (Decoder, Decoder, Decompression) compressed data. However, depending on the situation, compression algorism or encoder-decoder is just called codec. A movie file is made of audio and video data, and the data is compressed and saved to reduce the file size. (When the data is not compressed, the file size can be increased by up to 100 times its size.) The modules that compresses (Coding) during encoding and decompresses (DECoding) during video play are put together to be called CODEC. MPEG4, XVID, DIVX, WMV and etc are used a lot for video codecs and MP3, WMV, AAC and etc are generally used a lot for audio codecs.
- Reference: http://en.wikipedia.org/wiki/Codec
 
DSC (Direct Stream Copy)
General video conversion goes through decoding and encoding processes. Direct Stream Copy is a process that skips the aforementioned processes and crops the parts of the video or changes the container.
 
Baseline Profile
Creating partial limits to allow the (decoding) H264 (AVC) videos to play correctly in portable devices (cell phones, PMP and etc).
 
Normalize Function
If the volume of the original video is high or low, the function normalizes (equalizes) the volume to a constant level before converting.
 
Keyframe
Key frames are parts in between the video that contain information about the video file. When searching the video key frame will be used as the unit so if you make the intervals between the key frames short, it allows for more detailed search. However, key frame intervals that are too short will increase the size of the output file and lowers the size to quality ratio. Proper interval length between the key frames is usually 5 to 10 seconds.
 
Bitrate
Bit rate represents the data size needed to play an audio or a video file for 1 second. Increase in Bit rate setting will increase the quality of the video but the size of the output file will and the time needed for converting will also increase. CBR : Constant Bitrate., Regardless of the video content, uses the same Birate from the start to end to convert the video. VBR : Variable Bitrate., Applys low Bitrate to the parts of a video with less movements and applys high Birate to the parts of a video with lots of movements. Provides a video with smaller size and better quality.
 
Container Format
Container Format is a format that is needed to save the compressed video or audio data. The term is used as a container or a format for short. To make the compressed video and audio data into a one file format using codecs a certain format is needed. Such format is called a file format and AVI, WMV, MOV, MP4, OGM, MKV, RM and etc that we see commonly are the containers. Each container has different characteristics but does not define compression algorisms. Thus it is wrong to say things like "RM format has worse quality than AVI format". (There has been misconception regarding RM format due to the frequency of converting the file in low quality and low bit rate.)
- Reference: http://en.wikipedia.org/wiki/Container_format
 
MP3 (Codec)
It's an audio compression codec. Official name is MPEG-1 Audio Layer 3 and as you can tell from its name, it has been used in MPEG-1 standard. Usually called MP3 for short and the file extension for this audio codec is also .MP3. There is also an audio codec called MPEG-1 Audio Layer 2 or MP2 which is not used as much as MP3. MP3 has higher compression capacity than the MP2 so it's hard to see MP2 format being used.
- Reference: http://en.wikipedia.org/wiki/Mp3
 
MP3P
MP3P is the abbreviation for MP3 PLAYER. Often confusion is created because MP3 PLAYER is called as MP3.
 
MP4 (Player)
After MP3P has been incorrectly called as MP3, some Chinese companies started calling "MP3 Players with video playing capabilities" as MP4 to indicate that it's a better device than the MP3. The problem is that the term MP4 creates confusion with the words MPEG4 Codec or MP4 Container.
 
MP4 (Container format)
MP4 container is a file format defined by MPEG standard and has the .MP4 extension. This format is supported by many companies including Apple and Sony, and is playable with iPod, PSP and etc.
- Reference: http://en.wikipedia.org/wiki/Mp4
 
MPEG4 (Codec)
It's a video codec created by MPEG standard group. The codec shows a better compression rate than previously used mpeg1 and mpeg2. Divx and Xvid which are widely used these days are the modifications of MPEG4.
- Reference: http://en.wikipedia.org/wiki/Mpeg4
 
MS-MPEG4
It's a MPEG4 codec implemented by Microsoft. When it was first added to the Media Player, the codec could run on AVI format but after late 90s update, the codec was limited to run on ASF (WMV) format only. It seemed like MS was planning on abandoning AVI format and push WMV format but as a result DIVX3 was created. Currently, MS-MPEG4 can run with the AVI file again.
 
DIVX3
When MS-MPEG4 stopped running on AVI format, one hacker made the MS-MPEG4 run on AVI, changed the FOURCC from previous "MP43" to "DVI3" and started distributing the codec named DIVX 3. Furthermore, the codec was distributed with the WMA codec (only the code was modified to be used with AVI) that was changed into audio. Thus it is correct to categorize DIVX3 as a modified MS-MPEG4 (V3) rather than a separate codec.
 
DIVX4
Ironically, the video codec that has started out as DIVX3 became the starting point for directly creating and distributing MPEG4. OpenDivx and Divx4 were created as the outcome. The codec that was being developed under the name Project Mayo later disappeared as the developers purchased the Divx Company and turned it into a commercial project.
- Reference: http://en.wikipedia.org/wiki/DivX
 
DIVX
A codec that was derived from DIVX4 and turned into a commercial use codec. Different from DIV3 and DIV4.
- Reference: http://www.divx.com
 
XVID (Codec)
When DIVX4 turned into a commercial project, XVID was derived as an opposition and to remain as an open source project. XVID is DIVX written backwards, and remains as an open source project.
- Reference: http://www.xvid.org
 
OGG (Container format)
OGG Container Format is mistakenly known as an audio codec but the audio codecs are either Vorbis or Ogg Vorbis and OGG is a container format for containing multimedia data. OGG format can contain audio data using audio codecs such as Vorbis, Speex and Flac, and save video data by containing video formats like Xvid and H.264. When the OGG format contains video + audio data, you can create an OGM format video with GOM Encoder by using the .OGM extension.
 
VORBIS (Codec)
Vorbis is an audio codec developed to counter the commercial use audio codes like MP3. Generally, it shows better compression rate than MP3. VORBIS file is usually created using OGG container and has the extension .OGG. VORBIS codec and OGG container are used together frequently.
- Reference: http://www.vorbis.com
 
AVC, H.264, MPEG4 PART10 (Codec)
The video codec has been developed most recently and has the highest compression rate. It's called in various names like AVC, H.264, MPEG4 PART10 and etc but they all mean the same thing. The codec is known to have a compression rate twice as higher than the previous MPEG4 (DIVX, XVID included). To implement high compression rate the algorism is complicated and to play the file high CPU power is required.
- Reference: http://en.wikipedia.org/wiki/H.264/MPEG-4_AVC
 
AVI (Container format)
It's a video container developed by Microsoft. At first it saved the video with uncompressed video and audio data, but was later recognized by the users as high quality video format thanks to the emergence of compressed video files using MS-MPEG4 and MP3. Due to the characteristics of the format it's complicated to use the OGG file with the audio codec and there are rarely any video files using OGG audio.
 
MKV (Container format)
It's one of the video containers like the AVI. Compared to the AVI file, it has better efficiency of saving extra files other than codec, and when same codec is used, MKV will have a smaller file size than AVI. (Thus MKV can save a data with higher Bit rate when using same size.) The usage is increasing since the format has many good characteristics but the number of devices or programs supporting the format is still low.
- Reference: http://www.matroska.org/technical/guides/faq/index.html
 
* The codecs can be categorized as the following.
- Audio Codec: MP3, VORBIS, AC3, DTS
- Video Codec: MPEG1, MPEG2, MPEG4, XVID, DIVX3, DIVX4, DIVX, H.264
- Movie Container Format: AVI, OGM, FLV, MP4, TS, RM, MKV, MOV

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