How to make sense of video file formats?

Question

In digital video, there are all these different kinds of files: m4v, mov, mkv, mts, mp4, mpeg, and a host of others, and I can't seem to find a clear answer as to what each is good for.

(By contrast, when you're taking still pictures, you have two choices: JPG or RAW; with JPG, you basically know what the file contains, and with RAW, it's going to vary by camera manufacturer. I know it's a little more complicated than that, but it's nothing like the explosion of options available in digital video.)

Furthermore, it seems like the video's file extension doesn't tell you what's inside the file. From what I understand, a .mov file (for example) could contain just about anything.

Then there is this whole thing about h.264, AIC, ProRes, iFrame, AVCHD, DV, HDV -- at least I think those all belong to the same category, but I'm probably mistaken.

Can anyone help me understand all the different variables that are in play here so that I can make intelligent choices about what I do with the files coming off my camcorder?

Answer 1

File formats are essentially wrappers, a container of sorts. The video information is encoded in a codec (Coder/Decoder). Some file formats only work with certain codecs. This is due (in part) to corporate/organizational pissing contests (or format wars - remember dvd+ vs. dvd -?). Codecs come with varying degrees of compression. The more compressed a codec is, the smaller your files will be, but they will also potentially be losing information, in the same way that a RAW file saves everything from CCD, and JPEG compresses the file by dropping repeated information. Also, most pro level NLEs (like Final Cut Pro (not FCPX)) play nicer with codecs that are less compressed. The more compressed it is the more the computer has to work to decode and re-enconde the information when you make changes (moving on the time line, cutting, adding effects etc.)

Recommendations: For recording and editing (HD), pick a low compression, high quality codec such as DVCProHD, AVCHD, Apple ProRes.

To export for sharing I recommend H.264. It is supported nearly universally and is very good quality with relatively small files. BluRay videos are actually encoded in an ultra high quality H.264

One other note: if your camcorder saves files in a weird format (ie. not mov, mpeg, mp4), you will need to use a transfer process in your NLE. Be sure to save the ENTIRE folder structure from your memory card, not just the mts, mxf, or whatever files.

More tips: if you're not sure what codec a file is in, you can open it in QuickTime and hit cmd+i to open the inspector window. It will have all the codec information there. Additionally, on Windows there is a small utility called G-SPOT which can show you what codec are you using on that file etc.

Answer 2

I don't know an incredible amount about video codecs, so I'll explain my top two and why I use them.

The MP4 format is designed to take up a small amount of space, this makes it good for sharing online and recording on devices with limited storage. The drawback is that you lose an extensive amount of quality, especially in particularly dark footage. The mpeg format is also proprietary, meaning if you edit on Linux you have to buy the codec.

AVI is a very nice format. It isn't proprietary and there is very little loss in quality. This means AVI files can be very large, but I always use the format whenever it's feasible because of the quality.