digitalFAQ.com Forum - Wrapper vs. Codec

Hello Everyone,

First let me say I really appreciate the help and information I’ve found at this site. I can see the knowledge runs wide and deep here and that is why I’m asking for help in my quest to understand nuances of digital video—specifically the wrapper vs. the codec which I think is the culprit here.

For quite some time I have been digitizing my old family (S)VHS collection using my JVC DVHS deck as described in this post http://www.digitalfaq.com/forum/vide...-workflow.html with some success. Through the post I’ve learned this might not be the best way to capture but I’m using it for now as the results seem reasonable until I collect additional equipment. Part of my workflow was to use the timer function in the AVCVideoCap program to set an estimated length of recording so I could do other things during the capture and, if I forgot to stop the recording, I would still have a capture of reasonable length and size. This did however result in some captures that had excessive blank sections at the end. In the post I asked if anyone knew of a program that would let me trim the capture without re-encoding and between then and now, I found one. It is called “Bigasoft Total Video Converter” and hidden in some of the codec formats under “Advanced,” is a function called “Copy” that does not re-encode the video. This is where my puzzlement begins that I think is related to the codec vs. the wrapper.

The capture from AVCVideoCap results in a MPEG2 Transport stream with a .m2t extension that I found QuickTime and Final Cut Pro X didn’t like. Purely by accident, I discovered that if I changed the extension to .m2ts, (by the way, I’m using a Mac) both of these programs would accept the files and I could play or edit however FCPX slowed to a crawl whenever I imported and tried to edit these files. So, my workaround to this point was to import the file, wait for FCPX to do its thing and then immediately export the file to Apple Pro Res 422 then close the library. I had to close the library because if any of the imported media in the library was in the Transport Stream format, FCPX would slow to the point of being unusable for editing. I would then open a new library to import the converted file. This resulted in FCPX running at normal speed so I could edit without slowdowns or stalls. It was time consuming, but it worked.

By now you are probably wondering what is the point of this long description. Well, today I tried using the copy function in Bigasoft Total Video Converter. I trimmed a two-hour video to a one-hour video and BTVC copied it to a new file in about a minute, so I beleive it was not transcoding the file. The copy function is not available in all export formats, so I used the QuickTime .mov format figuring what format I chose wouldn’t matter since I was copying not transcoding. When I finished copying the file, I changed the extension back to .m2ts since I thought the unaltered original video would need the original extension to play but to my surprise QT, VLC, and FCPX all refused to play the file indicating they simply couldn’t play, or in the case of VLC, “no description available for this codec.” In an act of desperation, I changed the extension back to .mov and guess what, the file played perfectly in all the programs. Even more surprising was when I imported it to FCPX, it did not suffer any slowdowns and I could edit normally. The file still reports as an MPEG-2 file but Interestingly, QuickTime’s inspector does show some changes where the original .m2ts straight from the DVHS reports to have a 9.93 Mbits/sec bitrate and a pixel aspect ratio of 10:11 and the copied .mov file reports as 11.86Mbits/sec and an 8:9 Pixel ratio. I don’t think BTVC did any transcoding since the copy was way too fast, so I am not sure why the change.

So, after all this and I apologize for the long post, I there any information available about the wrapper and codec? I did look through the site and found the post about Gspot but I haven’t found details about wrappers(containers)/codecs. I know they are not the same but I would really like to understand what I’m doing and thank everyone for their help/suggestions so far.