Is Rendering Re-encoding? Is that Bad?

[Avagadro1]

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[poisondeathray]

Not sure about Elements, but for Premiere Pro - rendering is re-encoding - but it's only used for previews. All the layers, effects, edits are "flattened" or "baked" and precalculated (similar to photoshop) to make editing easier . It's usually a lower quality, easily decodable format, just for preview purposes.

But the final export will not use that, unless you checkmark "use previews" in the export settings. By default it's uncheckmarked and it will re-calculate everything from scratch (slower, but higher quality), instead of using the preview

If Elements does not have that option, it's probably not using the previews for the final export. You can try to be extra safe by deleting the rendered files and cache before exporting, that will force it to re-render everything anyways from the original source files

[johnmeyer]

If you render to a new file AND if you then bring that file back into your editing program, you will then have permanently degraded your video. Each time you do this, you will add another layer of compression artifacts.

There are two ways to avoid this.

Poison already mentioned the first: if your editor (NLE) supports it, let it render temporary video files which are inserted as proxies on your timeline so that playback returns to normal speed (the only reason things slow down is that your editor is being forced to create the effects and compositing on the fly, and once you modify your video, each new modification will require more computer power and eventually even the fastest computer can't keep up, and the playback gets choppy).

The second solution is to render to an external file and then re-import that file, but when you do this, you render using what is called an "intermediate codec." This codec is specially designed to produce virtually no artifacts, and is also designed to let you create multiple generations (think of a Xerox "copy of a copy of a copy of a copy") without you being able to see any visual degradation. The files are quite large (although not as large as a lossless codec or uncompressed video). The best-known of these is Cineform. That company made a living for over a decade selling this professional piece of software for over $1,000. Yes, $1,000 just for a codec.

Fortunately for all of use, Cineform was purchased by GoPro who made that encoder available for free as part of its GoPro Studio. I'm not sure Studio is still available, but you could look. If it isn't, there are now other intermediate codecs available. Just Google "intermediate codec." You also may find that one is built into your editor. The various versions of Vegas include one.

[edit]One other intermediate codec advantage I forgot to mention is that they are specifically designed to give you smoother playback than the complicated h.264 or h.265 codecs used by many modern video cameras. This will let you add far more fx and do more compositing before the timeline performance begins to degrade again.

[Avagadro1]

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[poisondeathray]

In Adobe , when you "render a preview" , it does not mean exporting a video file then re-importing it. It means staying in the program and rendering an area so you can get real time playback. eg. Maybe you have some sections that are very effects heavy and slow everything down

For Elements, look here
https://helpx.adobe.com/premiere-elements/using/previewing-movies.html#render_an_area_for_preview

(I doubt Elements has it, but you can specify a lossless codec for preview files; so when you check "use previews" when exporting, it's faster (doesn't have to re-render), and there is no additional quality loss)


Of course you can export out some format then re-import it too. If you choose a lossy codec, then yes there is generational quality loss. High bitrate, near lossless codecs like cineform or others minimize that quality loss. There are also lossless codecs, but filesizes are much larger

When you save a project, that is just clip references specifying the edits, what you did, and metadata. Nothing is rendered when you save a project. When you open that project a few days later to continue, it just references the original clips and edits. It has to re-calculate everything unless there is a cache. No quality loss when re-calculating.

In that Elements link

Similarly, preview files can save time when you export the movie because Adobe Premiere Elements can use the information stored in the preview files rather than render again.

So that implies what I said above, there should be a checkmark for "use preview files" on final export. Don't checkmark it and you will force re-rendering from original assets


Another technique is proxy editing, but I don't think Elements supports it. You edit with low resolution files , so editing is "fast". But swap back to original assets on final export for full quality


You're dealing with VHS, SD, DVD - I doubt you will deal with performance issues, unless you have very old/slow computer , or have many layers / effects.

[Avagadro1]

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[poisondeathray]

It was only a couple of days ago that I learned on this site that "rendering" was a form of re-coding --- and read the warning that re-coding should be avoided (cropping and resizing was particularly frowned upon).

Yes; but there are times when you have to "render" and re-encode , it's unavoidable - For example, your output DVD . The point is to avoid lossy re-encoding as much as possible. If you have to, then do it once.

From what you wrote (see above), I believe I now undersatand that when I temporarily close out of a project I am working on, and then close Premier Elements, I am NOT "exporting" the project file nor rendering it. I'm merely saving what was there. When I pick-up again the next day and load the program and the current project, then begin where I left off the day before, there is no rendering or re-coding. (I hope I've got that correct.)

Yes

But sooner or later while working on a project --- a complex edit, or several edits --- these may cause the program to slow down while it is trying to figure things out. So the advice in the common instructional books is to invoke a render. What I believe I now understand is that if at this point I render the project (or a part of it), the re-coding is present ONLY in the Preview Files, not the actual project file. (Is that correct?) So there is not at this point any degradation of the project file, notwithstanding the render. (I hope I have that correct.)

Yes. The project file references the original clips. There is no degradation

Now if I'm understanding your advice, you seem to suggest that I can do all the rendering I want; the re-coding is present only in the Preview Files. However, when all my edits are complete, I need to make sure that before exporting the project to a final format (burn to folder or to DVD), I must make sure that the program will NOT be using Preview Files. To make sure of this, you state that there should be a checkbox in the export dialog, which I must make sure is unchecked. (I don't recall ever seeing such a box, but I'll look again.) Another alternative you mentioned (in your earlier reply), is that I could save my project and close the program (thereby emptying cache). Go to the Premier Elements folder that holds the Preview Files and delete them all. Reload the program and project. Now when I export the project (burn to a folder or to a disc), I will be doing the ONE-AND-ONLY render of the entire project. I hope I have that correct.

Yes, but closing the program usually does not automatically empty the preview renders

In elements, for the render preview
Timeline > Delete Rendered Files
https://helpx.adobe.com/premiere-elements/mac-app-store/help/previewing-movies.html#de..._preview_files

Premiere pro also has a media cache; it's related but separate to the preview render. I'm not sure if Elements has this, but you might want to delete the cache files too

[Avagadro1]

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