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Digital Video for Multimedia: Digital Video on Trial

During our investigations into digital video for multimedia applications a series of experiments was performed to investigate the various parameters involved with video capture, such as choice of codec, frame rates, key frames, compression quality and siz e of video window. The results, a series of digital video clips, can be accessed and downloaded. Further information expanding on the issues already discussed in this report is also available, as are links to other sites with relevant information.

View the full report.

Further information can be obtained from other useful sites.

The tables below reveal some interesting facts about the nature of the various codecs listed. The nature of the relationship between quality level, compresson and file size varies from one codec to the next. The balance of tradeoffs is dependent upon the video material (content and quality) and its purpose. However, assessment of the various codecs is a subjective process and the results should be considered while viewing the files.

Method:

A video sequence containing several scenes with differing content (scenes with little change, rapidly changing scenes, scenes with multiple content and special effects, etc) was captured "raw" and using real-time compression at various frame rates and win dow sizes and compressed using a variety of different quality settings and codecs. The sequence was captured from a non-degradable video source, an analogue write-once laserdisc, to eliminate tape degradation effects and maintain quality. All sequences we re captured on a PC. Two cards were used in the study:

Results:

Table 1:
Compression times and file sizes for various quality settings and codecs using MS VidEdit, captured via Creative Labs Videoblaster RT300:

Initial file: 30 seconds of Intel raw video, 25 frames per second, 320 x 240, original file size 70.4MB. All files are at 24 bit colour except MSVideo1, as this only supports 16 bit colour.

Output settingsCodecConversion
time (minutes)		Size (MB)Output file
100% quality
key frame
every frame		MS Video 1
Indeo 3.2
Indeo
Interactive Cinepak		9:00
10:45
17:00
48:30		70.1
13
12.4
18.7
msvid_1.avi
ir32_1.avi
ir4_1.avi
cnpk_1.avi
0% quality
key frame
every 10
frames		MS Video 1
Indeo 3.2
Indeo Interactive
Cinepak 		2:50
14:15
43:45
33:10		0.61
2.65
1.79
18 		msvid_2.avi
ir32_2.avi
ir4_2.avi
cnpk_2.avi
Codec defaults
for quality and
key frame rate		MS Video 1
Indeo 3.2
Indeo Interactive
Cinepak		3:40
14:05
46:55
34.50		5.17
2.89
4.95
18		msvid_3.avi
ir32_3.avi
irv_3.avi
cnpk_3.avi
Comparing the conversions for MS VidEdit and Adobe Premiere there was no noticeable difference in either the time taken or the final file size. Adobe Premiere does afford the opportunity to output to the Apple Quicktime format. Corresponding times and file sizes are given in the table below.

Table 2:
Compression times and file sizes for various codecs at the highest quality setting, using Adobe Premiere

All starting with the same initial file, 30 seconds of Intel Raw video, 25 fps capture, 320 x 240, original file size 70.4MB

Output settingsCodecConversion time
(minutes)		Size (MB)Output file
quality 5
key frame
every frame
MS Video 1
Indeo 3.2
Cinepak		6:35
11:40
52:05		62.8
12.6
18.2		video_1q.mov
ir32_1q.mov
cnpk_1q.mov
Note: At the time of writing, the Quicktime format did not support the Indeo Interactive codec. Quicktime provides a quality setting range of 0-5.

Table 3:
A comparison of file sizes versus frame size

This illustrates the change in quality against frame size.

All files captured to RAM as Indeo Raw (via the Videoblaster RT300) and recompressed at 25 fps, highest quality, key every frame using MS VidEdit.

Frame sizeCodecFile size (bytes)Output file
160 x 120Indeo 3.2
Indeo Interactive		4420298
4420814		ir32_1.avi
ir4_1.avi
192 x 144Indeo 3.2
Indeo Interactive		6181010
6516170		ir32_1.avi
ir4_1.avi
288 x 216Indeo 3.2
Indeo Interactive		11681090
11399920		ir32_1.avi
ir4_1.avi
320 x 240Indeo 3.2
Indeo Interactive		13280700
12658408		ir32_1.avi
ir4_1.avi
640 x 480*Indeo 3.2
Indeo Interactive		1884426
3956890		ir32_1.avi
ir4_1.avi
*Note: The low file sizes here are due to the computer and card being unable to capture at 640 x 480. Captures were therefore carried out manually (i.e: frame by frame) and represent sequences of 100 frames (4 seconds).

Table 4:
A comparison of file sizes versus frame rate.

All files captured to RAM as Indeo Raw (via the Videoblaster RT 300) and recompressed at 320 x 240, highest quality, key every frame, using MS VidEdit.

Frame rateCodecFile size (bytes)Output file
25Indeo 3.2
Indeo Interactive		13280700
12658408		ir32_1.avi
ir4_1.avi
15Indeo 3.2
Indeo Interactive		7782486
7440252		ir32_1.avi
ir4_1.avi
12.5Indeo 3.2
Indeo Interactive		6597990
6331812		ir32_1.avi
ir4_1.avi

Table 5:
A comparison of file size versus codec using the Video NT card

Initial file: Approximately 17.5 seconds of Vitec 422 video (Vitec's form of raw compression), 25 frames per second, 192 x 144, original file size 25MB, recompressed at highest quality, key frame every frame, using Vitec editing software.

CodecFile size (bytes)Output file
Cinepak
MS Video 1
Intel Indeo 3.2
Intel Interactive
Vitec DCT		3792598
13669916
3264318
3441432
4484472		cnpk.avi
msvid.avi
ir32.avi
ir4_avi
vitec2.avi
Note: Vitec's own DTC (Discrete Cosine Transform) codec only gave us control over some of its settings; others were greyed out.

Table 6: MPEG files

Comparison of file size and quality settings of MPEG files created from either Indeo Raw at two different frame sizes, or compressed AVI files, using MPEG compression software (MPEG maker) supplied with the Video NT card.

Frame sizeInitial codecFile size (bytes)output fileMPEG compressor settings
192 x 144
file from table 3		Intel Raw
Intel Raw
Intel Raw		611884
1713813
2474927		hi_cmprs.mpg
quality.mpg
quick.mpg		default high compression
default high quality compression
default fast compression
320 x 240
original file
from table 1		Intel Raw
Intel Raw
Intel Raw		1223695
3250012
4823189		hi_cmprs.mpg
quality.mpg
quick.mpg		default high compression
default high quality compression
default fast compression
Recompressed
using files from
table 1		Cinepak
MS Video
Intel Indeo 3.2
Intel Interactive		4370476
4245941
3812733
4073239		ex_cnpk.mpg
ex_msvid.mpg
ex_ir32.mpg
ex_ir4.mpg		default high quality compression
default high quality compression
default high quality compression
default high quality compression
One sequence was captured directly to MPEG using the Vitek Video NT card at the "high quality" setting but - with the stuttering playback, general poor quality and time constraints - we did not consider it worthwhile continuing with this apporoach. The file is vitec.mpg.


Last Update $Date: 1996/10/23 14:53:10 $

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