Smart rendering in Adobe Premiere Pro accelerates the export process by copying previously rendered frames from the sequence's preview files directly to the output file, avoiding re-compression. To enable this workflow, the sequence's preview file format must be set to a codec that supports smart rendering. "I-frame only MPEG" is a specific, intra-frame codec option available in the Sequence Settings that is designed for this purpose. Using an I-frame (intra-frame) codec ensures that each frame can be processed independently, which is a prerequisite for efficient smart rendering of rendered effects.

A. H26A: Assuming this is a typo for H.264, it is a highly compressed, inter-frame (long-GOP) delivery codec, not an optimal intermediate format for sequence previews intended for smart rendering.

B. Quicktime: QuickTime is a container format, not a specific codec. While it can contain smart-renderable codecs like Apple ProRes, the option itself is not a specific format and is therefore less precise than "I-frame only MPEG".

D. RED R3D: This is a proprietary camera raw file format. It is used as source media and cannot be selected as a preview file format within Premiere Pro's sequence settings.

1. Adobe Premiere Pro User Guide

"Render effects in a sequence in Premiere Pro": In the section "Set up a sequence for previews

" the documentation states

"In the Sequence Settings dialog box

for Preview File Format

choose a format that supports smart rendering

such as I-Frame Only MPEG." This directly supports the choice of 'I-frame only MPEG' as a required option.

2. Adobe Premiere Pro User Guide

"Smart rendering": This guide explains the concept and requirements

noting

"To set up a project for smart rendering

you must choose a codec that supports smart rendering... These codecs include... I-Frame Only MPEG...". It clarifies that the codec must be suitable for re-encoding without quality loss.

3. Adobe Premiere Pro User Guide

"Export settings reference for Premiere Pro": Under the "Use Previews" setting description

it specifies

"For smart rendering of preview files

it is important that the preview file format is a smart rendering-capable format

such as I-Frame Only MPEG...". This confirms the link between the "Use Previews" feature and the required preview format.