AVI Files
AVI Extraction Files
EXAMPLE 1
> analyse_avi_file.tcl
You might want to cat the output to a file for easier viewing (i.e. analyse_avi.tcl > output.txt )
Interesting Items About AVI Files
Q. What information can you get from the parsing an AVI files?
A.
Q. How do you tell a AVI-1 bitstream from a AVI-2 bitstream ?
A. All AVI-2 bitstreams must have certain extension headers that *immediately* follow AVI-1 headers. At the highest layer, for example, the AVI-1 style sequence_header() is followed by sequence_extension() which is exclusive to AVI-2. Some extension headers are specific to AVI-2 profiles. For example, sequence_scalable_extension() is not allowed in Main Profile.
A simple program need only scan the coded bitstream for byte-aligned start codes to determine whether the stream is AVI-1 or AVI-2.
Q. What is the framerate of AVI's?
A. 30 frames/second
Q. What is the height and width the AVI's are saved in?
A. AVI-1 352 x 240 for the luminance(Y), 176 x 120 for the two chrominance
AVI-2 720 samples/line by 480 lines per frame
both are what is usually done, not the maximum of what can be done
Q. Can AVI-1 encode higher sample rates than 352x240x30 ?
A. Yes. The AVI-1 syntax permits sampling dimensions as high as 4095 x 4095 x 60 frames per second. The AVI most people think of as "AVI-1" is actually a kind of subset known as Constrained Parameters Bitstream (CPB).
Q. What are Constrained Parameters Bitstreams ?
A. CPB are a limited set of sampling and bitrate parameters designed to normalize computational complexity, buffer size, and memory bandwidth while still addressing the widest possible range of applications. CPB limits video to 396 macroblocks (101,376 pixels) per frame if the frame rate is less than or equal to 25 fps (frames per second), and 330 macroblocks (84,480 pixels) per frame if the frame rate is less or equal to 30 fps. Therefore, AVI video is typically coded at SIF dimensions (352 x 240 x 30fps or 352 x 288 x 25 fps).
The total maximum sampling rate is 3.8 Ms/s (million samples/sec) including chroma. The coded video rate is limited to 1.862 Mbit/sec. In industrial practice, the bitrate is the most often waived parameter of CPB, with rates as high as 6 Mbit/sec in use.
Q. What are the typical AVI-2 bitrates and picture quality?
A. AVAVAVAVAVI-1 (SIF) 1.15 Mbits/sec, AVI-2 (601) 4.00 Mbits/sec
Q. What are AVI-2 VIDEO Main Profile and Main Level?
A. AVI-2 Video Main Level is analogous to AVI-1's CPB, with sampling limits at CCIR-601 parameters (720 x 480 x 30 Hz). Profiles limit syntax (i.e. algorithms), whereas Levels limit parameters (sample rates, frame dimensions, coded bitrates, etc.). Together, Video Main Profile and Main Level (abbreviated as MP@ML) normalize complexity within feasible limits of 1994 VLSI technology (0.5 micron), yet still meet the needs of the majority of application users.
Level Max. sampling Pixels/ Max. Significance
dimensions fps sec bitrate
--------- ---------------- ------- ------- --------------------------
Low 352 x 240 x 30 3.05 M 4 Mb/s CIF, consumer tape equiv.
Main 720 x 480 x 30 10.40 M 15 Mb/s CCIR 601, studio TV
High 1440 1440 x 1152 x 30 47.00 M 60 Mb/s 4x 601, consumer HDTV
High 1920 x 1080 x 30 62.70 M 80 Mb/s production SMPTE 240M std
Note 1: pixel rate and luminance (Y) sample rate are equivalent.
2: Low Level is similar AVI-1's Constrained Parameters Bitstreams.
Profile Comments
------- -----------------------------------------------------------
Simple Same as Main, only without B-pictures. Intended for software
applications, perhaps CATV.
Main Most decoder chips, CATV, satellite. 95% of users.
Main+ Main with Spatial and SNR scalability
Next Main+ with 4:2:2 macroblocks
Profile
Level Simple Main Main+ Next
------------ -------------- -------------- -------------- ------------
High illegal illegal 4:2:2 chroma
High-1440 illegal With spatial 4:2:2 chroma
Scalablity
Main 90% of users Main with SNR 4:2:2 chroma
scalability
Low illegal Main with SNR illegal
scalabiliy
[Subject to change at whim of AVI Requirements sub-group]
Q. At what bitrates is AVI-2 video optimal?
A. The Test subgroup has defined a few examples :
"Sweet spot" sampling dimensions and bit rates for AVI-2:
Dimensions Coded rate Comments
------------- ---------- -------------------------------------------
352x480x24 Hz 2 Mbit/sec Half horizontal 601. Looks almost NTSC
(progressive) broadcast quality, and is a good (better)
substitute for VHS. Intended for film src.
544x480x30 Hz 4 Mbit/sec PAL broadcast quality (nearly full capture
(interlaced) of 5.4 MHz luminance carrier). Also
4:3 image dimensions windowed within 720
sample/line 16:9 aspect ratio via pan&scan.
704x480x30 Hz 6 Mbit/sec Full CCIR 601 sampling dimensions.
(interlaced)
Q. What frame rates are permitted in AVI?
A. A limited set is available for the choosing in AVI-1 and the currently defined set of Profiles and Levels of AVI-2, although "tricks" could be played with Systems-layer Time Stamps to convey non-standard picture rates. The set is: 23.976 Hz (3-2 pulldown NTSC), 24 Hz (Film), 25 Hz (PAL/SECAM or 625/60 video), 29.97 (NTSC), 30 Hz (drop-frame NTSC or component 525/60), 50 Hz (double-rate PAL), 59.97 Hz (double rate NTSC), and 60 Hz (double-rate, drop-frame NTSC/component 525/60 video).
Only 23.976, 24, 25, 29.97, and 30 Hz are within the conformance space of Constrained Parameter Bitstreams and Main Level
Q. What are some typical picture sizes and their associated applications?
A.
352 x 240 SIF. CD WhiteBook Movies, video games. 352 x 480 HHR. VHS equivalent 480 x 480 Bandlimited (4.2 Mhz) broadcast NTSC. 544 x 480 Laserdisc, D-2, Bandlimited PAL/SECAM. 640 x 480 Square pixel NTSC 720 x 480 CCIR 601. Studio D-1. Upper limit of Main Level.
Q. What information can you get from the header files?
A.
Q. What is the height and width of the files being sent?
A. From what I have read, it is cannot be found in the header files. The Real Player can play the video files at many different sizes.
Q. What file types does the Real Networks support?
A.
| Type | Extension |
|---|---|
| Mpeg File | *.ra *.rm |
| RAM Meta File | *.ram *.rmm |
| SMIL File Format | *.smi *.smil |
| Shockwave Flash | *.swf |
| Real Text File Format | *.rt |
| Real Pix | *.rp |
Q. What headers are in a AVI file?
A.
Important Links
People I Talked To About AVI Files