When you make a new video file from another, there are two things that can happen, and many don’t know the difference.
- The video and audio info can be copied from the starting file to the new one… which is easy, fast, and the new file is a clone of the one being copied.
- The new one can be ‘rendered’ bit by bit from the info in the original… harder for the computer to do, and something that takes time… often a long time... sometimes a very long time..
An example of copying video files would be getting them from a camcorder or camera to
the computer… copying whatever file is on them and not doing any conversion to another file type or a file with different properties. Another copy process is uploading a file from your computer to an online video host service. The speed of the copy process is quick, only limited by the equipment you’re using or bandwidth constraints when uploading. Being digital, the new file is identical to the original.
An example of a rendering is, after you upload your video to an online host such as YouTube, the service uses your file to make a different one from it. YouTube and most online services convert your uploaded file to a Flash file that fully aligns with the service’s requirements. The file you and others see playing on is a different one than what you uploaded.
You might think of a file upload as a one step process, but it's most often two steps, the copying followed by the conversion. The conversion is often the step that takes so long.
Another example of a two step process you might think of as one is the saving of a movie project in Windows Movie Maker to your DV camcorder. In this case the first part is the rendering of a big temporary DV-AVI file, and the second part the copying of the temporary file from the computer's hard drive to the camcorder.
I prefer doing two-step processes in two steps, not one. If there's a hiccup with one of the steps, you know which one it's in and you don't need to do both over from scratch.
About Quality
In theory a digital copy has the same quality as the original. In practice, issues can result in differences. If your computer can['t keep up with the the transfer rate of a digital video file from a camcorder mini-DV tape to your hard drive, frames of info will be dropped.
A newly rendered file is the same or lower quality as the original. As a rule of thumb, it can’t be higher in quality even if it has higher pixel dimensions. You can't make quality from what doesn't exist.
Many of my files uploaded to YouTube go up as stereo, but the new Flash files play back as mono. Similarly, the visual quality is often lower. The same files I upload to my own website play back at the same quality I upload…. there’s no conversion or rendering process taking place on my server.