Definitions
Alexander Noé, April 11, 2006
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- chunk
- A chunk is the smallest piece of data in an AVI file. A chunk can e.g. contain a video frame.
structure:
typedef struct {
DWORD dwFourCC;
DWORD dwLength;
BYTE bData[dwLength];
} CHUNK;
- CRC check sum
- A checksum that allows the detection (but not correction!) of errors in data read for example from a disc. A typical CRC checksum is a 32 bit value.
- deltaframe
- A frame which, unlike keyframes, only contains the differences to the
previous frame. A deltaframe can only be decompressed if the previous frame has already been decompressed.
- dropped frame
- A frame that doesn't contain any data. When replaying a dropped frame, the previous frame is displayed again. This
technique is used in AVI files to make one frame being displayed longer than another one, such as in 24fps/30fps hybrid files, which are stored at a framerate of 120 fps, with 3 or 4 dropped frames between 2 real frames.
- dwDuration
- The super index contains for every standard index it points to the amount of time it takes to replay all data that standard index points to. For Open-DML files created with VirtualDub up to 1.4.10 over 2 GB, the dwDuration values of the audio stream are corrupt.
- frame header
- MP3, AC3 and DTS streams contain some information about the frame (size, bitrate, samping rate etc) in the first bytes of each frame. AVI-Mux GUI doesn't support MP3-VBR / DTS streams with bad frame headers. Broken AC3 stream headers will not be copied either. If a broken AC3 stream header is encountered, the next valid one will be looked for. Any data between will be omitted.
- Index
- An index contains information about the position of video-, audio- or other index data. For AVI files, there are several types of indexes.
- legacy index
- This index is found in normal AVI files (called AVI 1.0 sometimes). It is always stored in one piece and points to video and audio data.
- super index
- The super index can only be found in Open-DML files. It is the upper level index of the hierarchic Open-DML AVI file index. It points to standard- or field index data. A super index shouldn't point to other super indexes
- standard index
- This one is also only found in Open-DML files. It is the lower level index of the hierarchic Open-DML AVI file index. It points to video- and audio data, using less space for
one entry than the legacy index.
- keyframe
- A keyframe contains, unlike a deltaframe, a complete frame. In AVI
terms, a keyframe can be seeked to very easily. In MPEG4-terms, it is not that easy: A B-frame succeeding such a keyframe could reference another frame preceding this keyframe. Then, the frame is still a keyframe, but not a so-called IDR-Frame. When storing MPEG4 in AVIs, reasonable encoders or muxers should only label IDR-frames as keyframes
- Mode 2 Form 2
- This is a possibility to store less error correction data to a CD and use the free space for own purposes. A sector can then contain 2324 bytes of user data instead of 2048. This is used for VCD and S-VCD for example. A "700 MB"-CD-R can then contain 798 MB without overburning. If you want to do this with AVI files, then please visit the homepage of Mode2CDMaker and read its readme-file carefully.
- Open-DML
- An extension to the AVI file format that allows the creation of AVI files larger than 2 GB. Open-DML files usually contain a hierarchic index structure with 2 levels (super- and standard indexes), and an additional legacy index is allowed. Read this to learn more or get the entire specification
here.
Warning: Many hardware divX Players do not want to read Open-DML files!
- rec-list
- A special structure in an AVI file that contains lots of video and audio data. Such a structure is read in one piece by all players I know,
so that larger blocks are read from the CD and less seek operations are necessary.
Warning: Some or all KISS players won't read files using rec lists. Disable rec lists if you intend to
play your files on KISS players!