I have Quick Time 10.1 and Mac OS X 10.7.5 I'm trying to open a MPEG-2 file but QT asks for a codec. What do I have to do?
What does "MPEG-2 file" mean to you? What is the file extension, audio compression format, and video compression format? What you may need to do depends on the specific nature of the problem involved. For instance, "muxed" MPEG-2/AC3 media should normally play if wrapped in an MPEG, MPG, or TS file container but the same data will not play in a VOB or MOV file container using QT X v10.1. In a similar manner, non-MPEG-2 compressed video data stuffed into an MPEG-2 file container will also not play.
the extension file is .mpg and it's a video mpeg with codec: MPEG-2 Video, AC3.
I have found these info in the proprierties of the file.
Can they help me?
Based on this information, the file would normally be expected to be compatible with your QT X v10.1 player. Suggest you next try to play the file in the free VLC player app. If the file won't play in that app, I would suspect something is wrong with the file. If the file does play in that app, then I would recommend checking into the compression specifications in more depth using a media information utility to see if anything obviously wrong stands out about the file.
the file plays with VLC: do you think that I need to update QT?
No, there is supposedly nothing to be updated if the information you previously provided is correct. If this is the only MPEG-2 file having problems, then the file itself needs to be analyzed to see if the issue can be traced to a specific causal source. Is the file small enough to be emailed as an attachment or can it be posted to a server for download and analysis?
If not interested in learning why the file won't play, you can always try converting the MPEG-2/AC3 content to an H.264/AAC file using the free HandBrake converter. Since VLC can play the file, it is likely that HandBrake can convert the file since both apps share the same FFmpeg open codec support.