Does pre-rendering a clip make the export quicker?

Hi there, I can't seem to find this question asked before..

If I have a bunch of clips which I pre-render, does this in turn make exporting the final video faster (as in, it's done some of the work already?).

I want to be able to pre-render my clips as I'm working on the project and then have a quicker export at the end...

Comments

  • Triem23Triem23 Moderator

    Go up to the File Menu at the top of the interface, and select "Options." 

    In Options look for the "Pre-render" tab. There you can select if Pre-renders are used on Export. 

    Using a Pre-render on Export should speed things up - particularly useful on complex comps with lots of layers and compositing/animation. Less so for straight video. 

    Bear in mind pre-renders are huge files (about 4 GB/minute for 1920*1080@24 fps), so if you're pre-render ing all video on input, you'll burn a lot of storage. 

  • edited September 11

    Hi Triem23, thanks for the reply. 

    Wow that is a huge amount of space! Why does pre-render take up more storage than the final rendered result? 

  • edited September 11

    @jonjuk

    Prerenders are so big because they’re very high quality... lossless quality from my understanding meaning that they are essentially indistinguishable from the original. This is why you can use them for the final export without worrying.

    They’re also much more optimized for editing- less compression allows them to be read much faster by Hitfilm.

    Usually, the best practice for Hitfilm is to film (or transcode your footage) to a format optimized for editing, and use pre-renders to play composite shots in real time.

  • Triem23Triem23 Moderator

    @jonjuk

    @triforcefx is correct. 

    Ok, so the formula for uncompressed video (no transparency) is video width*height*3*frame rate. For video with transparency it's width*height*4*frame rate. This gives Bytes. Now divide by 1024 for kbytes, then divide by 1024 to convert to Mbytes. 

    Let's try a 1920*1080 video with transparency at 24fps

    (1920*1080*4*24)/1024/1024=189.84 MEGABYTES per Second. That's over 10GB a minute!

    That same minute, exported with the YouTube preset should be a hundred Megs. 1% of the uncompressed.

    Pre-renders compress about 2:1 to 3:1, so that's my 4GB/minute from the earlier post. 

    Now, the computer doesn't have to work as hard to uncompress 3:1 as 100:1. This is why they are faster to work with. The trade is speed vs size. 

  • @trforcefc & @Triem23 - thank you both for your detailed responses. I think I'd need a couple of extra hard drives if I was going to use pre-renders then!  Although I can see the benefit, the pros outweigh the cons (for me).

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