Sound and picture problems with trailer downloads

[Greenie1]

I am a newbie to this so apologies in advance for my ignorance. I have searched the forums for any solutions but have not found any. Firstly, I downloaded a trailer which played the sound but no picture. Downloaded the codec required, and the trailer now has a perfect picture, but the sound is barely audible.

Secondly, other trailers play sound perfectly, but the picture `judders' every few seconds. Presumably another codec is needed to correct this fault but I have no idea which one. Have tried Reclock Directshow Filter, but that did not work.

When i check all the affected files using Avicodec it informs me that I have the codecs needed for both audio and video.

Any suggestions to fix either of the above faults would be very much appreciated.
Thanks

[Vejita-sama]

Use Gspot to see which codecs you need. Look to the left under Tools.

[Greenie1]

Thanks for tip, but get the same results with Gspot, says I have correct audio and video codecs installed. Any further ideas would be welcomed.

Thanks