I have been creating rotoscoped video files from SA on my Mac. When the rotoscoping is finished, the file opens in QuickTime Player. When I close the file, I am asked to save it. The file is then "converted" to a new file. 

The original file is quite large. For example, my file AA_02a is 2.72 GB. The converted file is only 460.1 MB. They are both QuickTime movies. The original has an icon that is generic. The converted file's icon is a still from the movie.

I have visually compared the files at high magnification and find no difference, pixel by pixel.

Is it necessary to hold on to the original file? Has the conversion degraded the artwork in any way?  

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Quicktime Player X doesn't directly support some Quicktime codec types. So that's what the 'conversion' message is about. If you set your 'mov' file type in the finder to open up quicktime movies in Quicktime Player 7 you won't have that issue.

It's unfortunate that Apple doesn't directly support all of the Quicktime codec formats in Quicktime Player X. We don't have any control over that.

If you use one of the ProRes codecs, you shouldn't have the 'conversion' issue in Player X.

This isn't addressing all my questions. I don't necessarily see the conversion as a problem. I am wanting to know if the converted file is "less good" than the original file. The converted file takes up so much less space. 

If the converted file is functionally the same as the original, do I need to keep the original? Does the larger file have any advantages over the converted file? 

Additionally the converted file's icon shows a keyframe for easier identification of the file. The original, unconverted files all look the same in the finder.

Any time you run a lossy compression algorithm, you are going to lose something associated with the frame image. That degradation will compound if you later recompress with a difference codec. Whether or not that is a problem depends on the source material, the particular compression algorithm you are using, and your particular tastes.

So, if you are outputting from SA with a lossless animation codec, and Player X recompresses it with a lossy compression algorithm, then you are losing something. If you can't see a difference for your source material, then it's not an issue for you. If you can see the difference, then you might want to keep the original.

Uncompressed video codec formats do lead to huge video files. I mentioned ProRes because it is a lossy codec, so it is throwing away information, but it leads to a smaller movie file size and the compression seems to do a good job.

What video compression algorithms try to do is to throw away visual information that humans have a hard time seeing.  Your perceptual response to different spatial frequencies in an image varies quite a bit as the spatial frequency changes, so in theory you can get rid of the information you have a hard time seeing and end up with a reduced file size while not noticing much of a difference in the visual appearance of the frames.

Most video compression algorithms also take advantage of throwing away temporal information (time-varying information). This may result in a good appearance when watching a playing movie, but may result in more noticeable degradation of individual frame images. So if you care about that (how individual frames look when the movie file is not playing back), then that could be an issue.

I know you are asking for a definitive answer, but ultimately it really depends on your source material and what you want to do with it. 

i have found that once it is converted i cannot put it back in SA. the bigger file might look better but if you see no difference and have a problem with the amount of space on your computer i wouldn't keep the original.

For a long time, I used the ProRes 422(HQ) option, it was the format I worked with in both SA and FCP and later FCP X,  but once I saw (on a movie theatre screen) the “same” movie in 422 (HQ) and in 4444, I was sold on ProRes 4444.

If one’s work is completely computer generated, ProRes 4444 rocks.

But the files are hefty, a 100 GB file is very common here.

And festivals are now accepting ProRes files for screenings, no longer demanding DCPs as the imposed format (so it becomes fairly easy to send out the final copy via ftp, though not all festivals are able to go that way yet, large USB 3 keys or 2.5” portable hard drives are the favourite second option).

So much of that depends on your desired final output, if the work is ultimately going to be seen on theatre screens in festivals, then HD 1080p and ProRes really works, if the web is the final output, 720p and h.264 are great.

But be careful: if you plan on using a present piece as material for the making of a later one (I do that all the time, have done so for decades), it is best to keep it as uncompressed as possible, or you’ll eventually end up with porridge.

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