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Glossary
Glossary

Group Of Pictures

(synonyms: GOP)

In order to allow high Compression rates for digital video it may be encoded into GOPs, or Groups of Pictures, which consist of keyframes and delta frames. Keyframes are normal frames that consist of a complete picture, similar to a still image file format like JPEG. Keyframes may be followed by delta frames, which only include changes from the previous keyframe or even a previous Delta Frame.

Since delta frames are significantly smaller than keyframes, they typically make up the majority of a GOP. While this is helpful for keeping stream (file) sizes down, it makes editing more difficult since you're limited to cutting at particular frames to ensure every Frame kept can be decoded properly.

Frame Accurate Editing
Alternatively you can combine editing with re-encoding, or just re-encoding 1-2 GOPs to compensate for the missing information. Some video editors include either built-in encoding features or the capability to use an external encoder for this purpose. Others have no encoding capabilities and are limited in which frames must be kept.

MPEG GOPs
The most common GOP-based video formats are MPEG-1, MPEG-2, and MPEG-4. Each uses the same convention for the three types of frames used. Keyframes are called I or Intra-Coded frames, in reference to the fact that they're self contained and require no other frames to be properly decoded. There are two types of Delta frames, P and B, which stand for Predictive-Coded and Bidirectional-Predictive Coded respectively. P frames rely on information from the prior I or P Frame to be decoded. B Frames are also delta frames, but use information from the previous I or P frame, as well as the following I or P frame, making them smaller than P frames.

GOPs With Multiple Keyframes
Some video formats allow GOPs to contain more than one Keyframe. While this doesn't affect the encoding quality, it does minimize the GOP header information, which is typically written only at the beginning of each GOP. It may also restrict the frames you can cut at with a GOP accurate editor.

GOPs With No Delta Frames
Although GOP based video isn't generally well suited to editing, some encoders can create video streams with only I frames. Although they will still be divided into GOPs, since each frame is self contained no re-encoding is necessary no matter where edits are made. However, the resulting file will be significantly larger than one encoded with delta frames as well.

For more information, see the glossary definitions for:

Delta Frame I Frame Key Frame MPEG-1 MPEG-2 MPEG-4 VC-1

Related software tools:

3ivX D4 (BeOS) v4.5 (Freeware)
3ivX is an excellent video quality MPEG-4 codec for BeOS.

3ivX Delta Codec (Amiga 68k) v1.0d3 (Freeware)
3ivX is an MPEG4 codec based on the MPEG4v3 ISO standard.

3ivx MPEG-4 v5.02 (Commercial demo)
3ivX is an excellent quality video codec based on the MPEG-4 video standard.

3ivx MPEG-4 For Mac OS X v5.02 (Commercial demo)
3ivX is an MPEG-4 codec that allows playback of all MPEG-4 compliant formats, such as DivX, 3ivX and XviD.

Cinema Craft Encoder Basic (Trial) v2.67.01.19 (Commercial demo)
Cinema Craft Encoder Basic is an affordable, high quality MPEG encoder

Cinema Craft Encoder SP (CCE) v2.50 (Shareware)
Cinema Craft Encoder SP allows you to directly encode AVI, QuickTime and DV files into DVD or SVCD compliant MPEG-2 streams, or VCD MPEG-1 streams.

Cinema Craft Encoder SP (CCE) v2.70.02.06 (Commercial demo)
Cinema Craft Encoder SP allows you to directly encode AVI, QuickTime and DV files into DVD or SVCD compliant MPEG-2 streams, or VCD MPEG-1 streams.

Cucusoft MPEG/MOV/RM/AVI to DVD/VCD/SVCD/MPEG converter (Pro) v7.07 (Commercial demo)
Cucusoft Mpeg/Mov/Rm/AVI to DVD/VCD/SVCD/MPEG converter Pro is easy to use and powerful video converter for experts as well.

DGMPGDec v1.5.2 (Patch release) (Open source)
DGMPGDec is an MPEG2 Decoder and Frame Server, based on DVD2AVI and MPEG2Dec.

DivX v6.8.4 (Freeware)
The latest version of the DivX. That is, you need to have this file installed if you want to watch DivX movies. And latest codec gives you the best quality.

DivX (Win98/ME) v5.2.1 (Shareware)
The latest version of the DivX codec for Win98/ME platforms. You need to have this codec installed in case you want to watch or encode DivX movies.

DivX ;-) MPEG4 Codec release 3.11 alpha (Freeware)
DivX ;-) is a hacked MPEG4 codec that allows you to watch and encode DivX ;-) video clips. You really need this one, trust me...

DivX Create v6.3 (Shareware)
This is the DivX pack you want if you're planning to encode DivX movies on your own.

DivX for Linux v5.05 (Freeware)
Official DivX5 codec for Linux -- provides same features and same quality as the Windows version does.

DivX for Mac OS X v6.7 (Shareware)
DivX5 for Mac is _the_ official DivX codec for Mac -- it has been developed by DivX Networks, same guys who have developed DivX4 for Win. Excellent MPEG-4 based video codec.

DivX Pro (Win98/ME) v5.2.1 (Shareware)
DivX is an extremely popular implementation of the MPEG-4 standard.

DivX Pro for Mac OS (15 day trial) v5.1.1 (Freeware)
DivX5 for Mac is _the_ official DivX codec for Mac -- it has been developed by DivX Networks, same guys who have developed DivX4 for Win. Excellent MPEG-4 based video codec.

DivX Pro for Mac OS X (15 day trial) v5.2.1 (Shareware)
DivX5 for Mac is _the_ official DivX codec for Mac -- it has been developed by DivX Networks, same guys who have developed DivX4 for Win. Excellent MPEG-4 based video codec.

DVD-Rebuilder v0.98.2 (Freeware)
Free tool that makes it possible to shrink a DVD movie into single DVDR disc, using CCE as an external encoder, producing far better quality than any of the fast one-click tools.

FreeEnc v0.5 (Open source)
A libavcodec based encoder. This encoder takes AVS input and outputs MPEG2.

HC Encoder v0.23 (Freeware)
HC is a simple to use MPEG2 video encoder and is meant for creating MPEG2 video streams with a strong focus on DVD-compliancy.

ImTOO AVI MPEG Converter v5.0.97.0715 (Shareware)
ImTOO AVI MPEG Converter is able to convert avi to mpeg1,mpeg2,mpeg4 and mpeg1,mpeg2 to avi.

ImTOO AVI to DVD Converter v3.0.38.0801 (Adware)
ImTOO AVI to DVD Converter is a DVD burning software which can convert AVI to DVD and burn it on DVD disc.

ImTOO MPEG Encoder v5.0.94.0714 (Shareware)
ImTOO MPEG Encoder is an ultimate video and audio format converter.

NeroVision Express v3.1.0.21 (Commercial demo)
With NeroVision Express you can capture video and create impressive presentations in different video formats such as VideoCD, DVD, etc.

QuEnc v0.72 (Open source)
QuEnc is a free, good quality MPEG-1/MPEG-2 encoder, based on the ffmpeg encoding library. Works great with DVD-Rebuilder.

TMPGEnc v2.524.63.181 (Shareware)
TMPGEnc is an excellent shareware MPEG-1 and MPEG-2 encoder that can be used also for de/muxing, cutting, merging, etc. Superb tool!

TMPGEnc MPEG Editor (Trial) v3.0.5.69 (Commercial demo)
TMPGENC MPEG Editor allows you to edit MPEG video files at single frame accuracy.

TMPGEnc XPress v4.5.1.254 (Commercial demo)
TMPGEnc XPress is a completely redesigned version of the famous TMPGEnc MPEG encoder

VideoReDo Plus v2.5.6.512 (Shareware)
VideoReDo Plus is one of the most popular MPEG editors on the market.

x264 full rev. 928 (Open source)
x264 is a free library for encoding H.264/AVC video streams.

Xilisoft 1Click DV to DVD v1.3.7.0620 (Shareware)
1Click DV to DVD is ease-to-use DV to DVD converter which provides a simple way to convert and transfer Mini DV, DV to DVD-Video disc.

Xilisoft AVI MPEG Converter v5.0.98.0801 (Shareware)
Xilisoft AVI MPEG Converter is able to convert avi to mpeg1,mpeg2,mpeg4 and mpeg1,mpeg2 to avi.

Xilisoft Video Converter v5.0.60.0707 (Shareware)
Xilisoft Video Converter is a good video conversion tool. It can convert video files between various formats including DVD, VCD, SVCD, MOV, RM, AVI, MPEG-1/2/4, WMV, 3GP.

XviD Codec v1.1.3 (Koepi's 28.06.2007 Final Build) (Open source)
XviD is an open source video codec that lets you play and create MPEG-4 compatible videos.

XviD Codec v1.2.127 Beta (Koepi's 25022006) (Open source)
XviD is a MPEG-4 compatible codec, which produces very good video quality -- something that really competes with DivX.

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