(Temporal) Compression: Interframe

Interframe, or temporal, compression reduces file sizes by eliminating redundant information between multiple frames of video. This is achieved by identifying and encoding only the changes between successive frames and eliminating areas that remain identical between them.

For example, the background of an image may remain unchanged while the subject of the video moves throughout the video. Instead of retaining the unchanging background in every frame, it can be retained in the first frame and used for all subsequent frames.

The process begins with selecting a keyframe (also called an I-frame) which is a fully intact frame and will serve as the reference for subsequent frames. Following the keyframe are P-frames and B-frames which will not be retained in full. Instead, only the changes relative to the keyframe are saved. P-frames (Predictive frames) store changes based on the preceding frames. B-frames (Bi-directional frames) retain information from both previous and subsequent frames in order to determine the minimal changes needed to represent the original video. This drastically reduces the amount of information saved in each video frame and subsequently significantly reduces file size. While it is efficient in file size reduction, it can affect image quality and introduce artifacts in situations with fast-moving and unpredictable elements.

Used for: Viewing

Adobe Premiere Pro is a videly used video editor, however, it has a considerable flaw when it comes to using the applicatino for ‘industry standard’ work.

Premiere Pro defults to 8-bit. Worse, effects that don’t feature GPU acceleration will crush the clips they are applied on down -to 8-bits.

Why does this matter?

A bit-depth of 8 limits each colour channel to 256 possible values. While this limitation is fine for delivery, it produces compression artifacts in various post-production workflows and is actively desctutive to any to footage recorded at a higher bit-depth.

Unless Premier Pro is setup correctly, all imported and exported footage will be reduced to 8-bit. Even when setup correctly, certain FX with Premier Pro descructively reduce the bit-depth of correctly imported video files.

For this reason I prefer not to use Premiere Pro.

The Solution:

As stated, there is no way to force all aspects of Premiere Pro to perform in a >8-bit space, however, the Frame.io article below outlines the best practices for setting up Premiere Pro and Premiere Pro projects.

https://blog.frame.io/2021/06/07/premiere-pro-max-render-quality-max-bit-depth/

DaVinci Resolve: All Things To All Editors

Blackmagic’s DaVinci Resolve has been, for some time, the most accessible media application capable of industry standard workflows.

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Intraframe: (Spatial) Compression

This technique compresses each frame individually by eliminating redundant information within a single frame. This is achieved by analyzing segments of the image and identifying regions with minimal variation and representing them more efficiently.

For example, the clear blue sky in the image below has very little variation between pixels, so those regions can be represented by a larger block of uniform color and texture. This reduces the amount of information that needs to be retained and will not drastically affect the final image quality.

In contrast, the areas with more complexity and color variation cannot be compressed to the same degree and more information needs to be retained in these regions. Spatial compression thus reduces file size while maintaining a high-quality image by retaining information in complex and highly detailed regions while reducing information in simple and less important areas.

Used for: Working

Container Support:

DCP

MXF

XAVC

MOV/ProRes

DNxHR

Premier to Davinci round-trip

What are EDL, XML, and AAF files?

EDL, XML, and AAF files reference the information and structure in your editing timeline such as your source media, in and out points, edits/cuts, duration, transitions, markers, etc. These files are used to rebuild your exact cut in another software.

Because EDL, XML, and AAF files are used throughout the post-production cycle — not only for color — it’s important to understand how to export them in general, not just if you’re going to be using Premiere Pro and DaVinci Resolve. VFX artists use the same files, for example.

EDL (Edit Decision List)

This is the simplest of the three files. EDLs are plain text files that contain basic information about your edit from a single track of your timeline. It supports one video track and four audio tracks per EDL. This one is best used as a backup reference.

XML (Extensible Markup Language)

XMLs are also plain text files like EDLs but contain way more information, including things like sizings, transitions, time remapping, and other important metadata. XMLs support multiple video tracks, unlike EDL files.

AAF (Advanced Authoring Format)

Last, but definitely not least, AAFs. This one is a multimedia file format and can include video, audio, and other important metadata needed to recreate the exact cut in another software. AAF is the one that includes the most data out of the three and therefore the heaviest.

Software Compatibility