A common question on the forum is about CODECs. So I've decided to leave a list of sites that offer codecs.
It is best to choose one CODEC package ONLY for your system (more than one codec pack installed can cause problems.) Also consider a Video player with in-built codecs as listed in 4th paragraph (we highly recommend VLC player); VLC & MPlayer seem to be best / most reliable ones & recommended to have both players just in case.)

A list of CODECs sources can be found here (choose one of these sources): 1. Free-Codecs.com, __ 2. DivX codec A / DivX Codec B, __
3. K-Litecode Codec Pack, __ 4. XP Codec Pack 1.3.0, __ 5. Vista Codec Package v4.4.7 Beta 4a (freeware) / More direct link to current version,
6. MS WMP codecs, __ 7. divx-digest tools & codecs, etc., __ 8. Combined Community Codec Pack (CCCP) (Good H.264 support),
9. 3ivx codec to allow mpeg 4 audio & video playback, ____ 10. Codecs list,
11. TMPG encoder & burner (TMP is for burning dvd's, VCD's, etc. only!)
Mac OSX users see Problems watching videos in Mac OSX - Read this, ___ Converting Video to iPod & playing WMV, WMA, FLAC & Ogg Vorbis in iTunes


* Get Get GSpot (click on link) it's free and it will tell you what you need to play a certain file.. just open the file in GSpot and it will tell you. (GSpot has not been updated in a while!) An alternative to GSpot is MediaInfo (click on link). Another is SHERLOCK - The Codec Detective!. Another is afreeCodecVT. A list of various codec identifiers here.


* Consider getting a back-up player with in-built codecs such as (i) DivX player (DivX player cannot play all video formats), or
(ii) VLC : VLC media player - Overview (choose nearest mirror site.) See its VLC Features. FYI see wiki description here. And How Can I load A new Skin In VLC Player?
Similar to VLC is (iii) MPlayer (click link to find wiki details) which is another cross-platform video player for unix, mac, & windows systems. It has in-built codecs, you can also install some extras to give it a much broader support base. Main download site is here. There is also MPlayer - The Movie Player - Unofficial Packages which give some more up to date playback options. We recommend having "both" VLC & MPlayer on your system since there's the odd thing each other one can't do. MPlayer can play specific VOB files for example, & also better at playing .MOV files. MPlayer also has support for RealMedia & ASF files (see list here).
(iv) Media Player Classic (click link to find wiki details) is another open-source alternative player (for Windows OS only.) Media Player Classic download site. It has limited internal plug-ins & for other codec types relies on those installed on computer. You can even change picture size (strech or compress) while watching the movies. Very good for those Widescreen DVDs and Screeners. Options to stretch etc. are found using NumLock and then the numbers. 5 is normal, etc. Also with Numlock on you can put delay on audio for those out of sync videos using +/-.


AVI specific players: 1. Hyplay, 2. Karawin


A handy Video editing & Conversion tool for Windows & Mac OSX: MPEG Streamclip (free) __ Supported input formats: MPEG, VOB, PS, M2P, MOD, VRO, DAT, MOV, DV, AVI, MP4, TS, M2T, MMV, REC, VID, AVR, M2V, M1V, MPV, AIFF, M1A, MP2, MPA, AC3, ... MPEG Streamclip lets you play and edit QuickTime, DV, AVI, MPEG-4, MPEG-1; MPEG-2 or VOB files or transport streams with MPEG, PCM, or AC3 audio (MPEG-2 playback component required); DivX (with DivX 6). MPEG Streamclip can export all these formats to QuickTime, DV/DV50, AVI/DivX and MPEG-4 with high quality encoding and even uncompressed or HD video. Used with the QuickTime Pro format or even just QuickTime equivalent, and MPeg Streamclip's internal H.264 (x.264) codec & exported as AVI/mp4 format is ideal & makes for high quality videos. MPeg Streamclip video encoded as H.264 (X.264) is better quality than DivX encoder. MPeg Streamclip can convert videos for iPod & is free!!!


* How to set the Default video application on Windows (click on blue link)

* How to change default program in Mac OSX (click on blue link)


What you should know about downloading videos (click on blue link) - (which video formats to download, which sizes, etc.)


Other video questions:

A: Video Help Forum & B: DVD guides forum, C: Video Tools (see the list, but you can also search more specifically for what you're after), & D: From video card to TV, E: Mac video tools, F: Linux video tools