Hi, all, I am a newbie in encoding videos. However, I could not find any source that compares the three codecs so that I decided to do one. The reason I did this is because I recently downloaded some files encoded with the three encoding methods; I wanted to edit them and then output them in their orignal format; and I wanted to edit some other files and output them using the most efficient encoding method. Therefore, I found the three encoders and installed them and did a test. The details are as following.

The following record is a result of encoding the same segment of a source video with three encoders. The Video bit rate setting was the same--all set at 700Kbps, constant bit rate. Most of the settings are default settings. However, the output video files have different video bit rate measured--so, even with the setting of constant bit rate, the resulting video bit rate didn't match what was intended. All encodings were 2-pass.

Encoder Versions: WMV3--Windows Media Video 9 vcm, XVID--XviD-1.1.0, and DX50--DivX 6.1.1

Type / File Size (bytes) / Video Bit Rate (Kbps)
:WMV3 / : 2553682 / : 793772
:XVID / : 2287984 / : 696514
:DX50 / : 2307316 / : 703590


File Size Ratio / Video Bit Rate Ratio
WMV3:XVID=1.116 / WMV3:XVID=1.139 (this comparison method bases on the assumption that the two encoders in consideration would have the same video bit rate in the output files. Then, Video Bit Rate Ratio of 1.139 is larger than File Size Ratio of 1.116; WMV3 file size has to increase or XVID file size has to decrease to yield a ratio of 1.139) Result: in fact, WMV3 didn't increase, so its file size must be less than Xvid if both have the same bit rates. WMV3 has higher compression than Xvid. Example %diff = l(Xvid file size X 1.139 - WMV3 file size)l / Xvid file size = 2.3% ; WMV3 has 2.3% lead in compression. The rest of the %diff's use the same concept)

WMV3:DX50=1.106 WMV3:DX50=1.128 Result: WMV3 has higher compression than DX50
%diff = 2.1% WMV3 has 2.1% lead in compression.

DX50:XVID=1.00845 DX50:XVID=1.01016 Result: DX50 has higher compression than XVID
%diff = 0.17% DX50 has 0.17% lead in compression.

Compression comparision: WMV3(highest compression) > DX50 (2nd highest compression)> XVID (3rd highest compression)
Compression Status doesn't indicate picture quality status? I think compression status doesn't indicate picture quality.
The calculated differences in compression between these three formats are small. DivX and Xvid compression are very close with %diff of 0.17%. Actually, I consider them the same.
However, WMV compares to the other two formats showing a small and also significant difference in compression--an average of 2.2% lead.

If there are any opinion, suggestion, and expert advice, please tell me. I am eager to learn.