Written by darkmafiaguy.
Most movies you download nowadays are made in the AVI format. There are two types of AVI's generally, uncompressed and mpeg4(DivX, XviD). To run these files, you need third party software. If your files are not working properly, please follow the instructions in this guide before posting for help. Thanks.

1. Video not working
If you open up an AVI file, and the video does not play (or your player reports that it cannot find the proper codec) chances are you don't have the DivX or XviD codec. A codec decodes information to play video.
To find out how the AVI file you are trying play is encoded, download a program called GSpot which identifies the format in which the video and audio is encoded in:
http://www.free-codecs.com/download/GSpot.htm
After opening the file in GSpot, look in the codec area inside the Video box so figure out which codec it uses. If it says DivX then head over here to install the DivX codec:
http://www.free-codecs.com/download/DivX_Free.htm
If it displays XviD, install either one of these:
http://www.free-codecs.com/download/Koepi_XviD.htm
http://www.free-codecs.com/download/Nic_XviD_Codec.htm
After installing, you may need to restart your computer. Then run the avi file and the video should play.
Sidenote: If it says Mpeg-2, then you need an Mpeg-2 codec:
http://www.free-codecs.com/download/Stinky_MPEG_2_Codec.htm
2. Audio not working
If you open up an AVI file, and the audio does not play it probably means the audio is encoded in AC3 (a 5.1 channel sound format) or the more uncommon DTS (another higher quality 5.1 channel sound format). To play either one of those, you can install AC3Filter:
http://www.free-codecs.com/download/AC3_Filter.htm
Make sure to downloaded the newest one, as the older AC3Filters do not support DTS. After installing, play the AVI file in your media player and the sound should work.
If you find out, using GSpot, that you have an OGG audio stream, use Media Player Classic:
http://www.divx-digest.com/software/media_...er_classic.html
(Thanks to Awdark.)
3. Subtitles not working
Subtitles generally come in the .srt (Subrip) or .sub formats. In both formats, there is raw text which gets read and played, unlike subtitles in DVDs which are images. There are a few option you have in playing these subtitle files. The first thing you should do before using any of these methods is to put the subtitles in the save folder as your avi files and with the same name. For example, if the name of your avi file is "Two.Guys.DivX.DVDRip" then the subtitles should also be named, "Two.Guys.DivX.DVDRip" If you have extensions showing, leave the extensions as they originally were. The first option you have in playing subtitles is using a plug-in called VobSub:
http://www.divx-digest.com/software/vobsub.html
It will directly render the subtitles to the video in realtime. What does this mean? It allows you to use it with any media player and it will also display the subtitles for you into video automatically if your converting it in certain programs. This is great when using unconventional media files, such as RM. After installing it, just play your AVI files and the subtitles should automatically be played by VobSub. If it doesn't work with VobSub, use the following method.
Another way, to play subtitles is to use a different media player altogether which supports subtitles. I prefer this method because I find VobSub a bit glitchy. The one I use is called BSPlayer. Download:
http://www.bsplayer.org/
After installing, run the AVI file in BSPlayer, and the subtitles should automatically load. Using BSplayer, you can do a couple of nifty things relating to the subtitles. To move them up or down, (which is useful in fullscreen mode) hold shift and press the up or down arrow keys. To correct the time, hold Shift and press the right and left arrow keys to move the subtitles times forward or backwards respectively in 200 ms increments.
Alternatively, you can use a program called Subtitle Workshop to permanently edit the subtitle file to your liking, this includes shifting the times to correct the time:
http://www.divx-digest.com/software/subtitle_workshop.html
Thats all for now, check back later for more troubleshooting information!

THANK YOU!