Two freewares to help you identify the Codec of a video files

GSpot is a Windows-based freeware designed to identify codecs used in video files. In addition, the application checks if the required DirectShow filters or Video for Windows codecs are installed and configured for proper playback. While originally created to support AVI, it was expanded to include full support for Ogg and limited support for other commercial container formats, including versions of MPEG, QuickTime movie, and Windows Media Video. Due to its ceased development many long-time users have turned to MediaInfo for the identification of newer video files (ie .m2ts files).

MediaInfo is a free and open-source program that displays technical information about media files, as well as tag information for many audio and video files. It is used in many programs such as XMedia Recode, MediaCoder, eMule, K-Lite Codec Pack, Media Player Classic Homecinema, etc. and can be easily integrated into any program using a supplied MediaInfo.dll. MediaInfo supports popular video formats (e.g. AVI, WMV, Quicktime, DivX, XviD) as well as many lesser known or emerging formats (e.g. MKV, OGM, Real). MediaInfo provides a GUI for easily viewing the information.

MediaInfo reveals information such as:
General: Title, author, director, album, track number, date, duration
Video: codec, aspect ratio, fps, bitrate
Audio: codec, sample rate, channels, language, bitrate
Text: subtitle language
Chapters: numbers of chapters, list of chapters

MediaInfo supports just about any video and audio file including:
Video: MKV, OGM, AVI, DivX, WMV, Quicktime, Real, Mpeg-1, MPEG-2, MPEG-4, DVD (VOB), DivX, XviD, MSMPEG4, ASP, H.264 (Mpeg-4 AVC)
Audio: OGG, MP3, WAV, RA, AC3, DTS, AAC, M4A, AU, AIFF
Subtitles: SRT, SSA, ASS, SAMI