the Blender Velvets

Velvet Revolver – Proxy editing



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Introduction to proxy editing

High resolution videos pose a heavy load on the system at the moment of editing. This happens not only because of the frame size but also because cameras, when recording, typically use temporal estimative codecs (such as the h264) to compress the files, increasing the CPU that has to be used to decompress them and generating imprecision during cutting, due to the interval between keyframes that store the main information.

That’s why, when starting an editing project, it is common to decrease the resolution of the footage and, when doing so, use intraframe compression codecs such as the ProRes or the MJPEG. In those codecs, all the relevant information regarding compression is stored in every frame, as opposed to in keyframes positioned at every 30 or 60 frames.

These smaller resolution files are called ‘proxies’ – a term used to define anything that will serve as intermediary, usually for a certain period of time, to get you to a certain end. In our case, we use videos close to SD (or standard definition) as intermediaries, so that our system gets lighter when doing the cuts, the most time-intensive task of the editing process. By the end of the project, we switch back to the high resolution files for color grading and final render.

Velvet Revolver aims to automate the generation of proxies so that you don’t have to worry about all the technical stuff. And once you will not want to start a complex editing project using videos in h264, or with different framerates (FPS) due to a Blender limitation in mixing them, the addon also allows for the creation of copies of your original material using the ProRes422 or MJPEG codecs, which are the best formats for video editing. Proxy generation or the creation copies at full resolution can be done together or separatelly. As shortcuts, Velvet Revolver uses Ctrl+Shift+P to make the timeline point to the high resolution videos and Ctrl+Alt+P to make it point to the low resolution versions.

Having said that, a typical description of an editing project using proxies would be: record the videos; copy them to the computer; use Velvet Revolver to generate the proxies and, if you want, full resolution copies in ProRes or MJPEG; let the machine work on this generation while you go do something else, such as have luch, get rest or go out on a date; use the proxies to do the cuts and establish a narrative line; do many intermediate renders still at SD resolution to check on how the video is getting. With the cuts made and when you get to a final version, the process is: use Velvet Revolver to point the project to the high resolution videos (at 720p, 1080p or higher); do the color grading and do the final render.

The table below, result of research made in early 2013 as part of the workflow for the Red Forest project, shows why it’s interesting to edit using proxies.

blender_render_tests2

A project that uses proxies in MJPEG and audio in PCM will generate the intermediate renders almost 4x faster than the same project in high resolution. The codec choice also influentiates radically the speed in which it is done: the same project using proxies and rendering using the MPEG4 and PCM codecs will do so 5x faster than if it used the H264 and PCM codecs, and 16x faster than a high resolution project rendering using the H264 and PCM codecs. All tests were made using the Matroska container (extension .mkv).

Notice that rendering the project during the editing phase is something that is done many times, making those numbers particularly relevant. The same observation is valid for renders that use still images as basis – something useful, for example, for final rendering, already with color grading done. Rendering frames in JPEG or TGA is quite faster than in TIF (7x and 4x, respectively) and brutally faster than using PNG (35x and 20x, respectively). See below.

blender_render_tests1

How to install Velvet Revolver

To install Velvet Revolver, click on the link below to go to the Download Area of the website.



Addons last update Aug 27, 2017 Go to the Download Area


Once downloaded, the file with Velvet Revolver (velvet_revolver.py) is inside a zipped folder, together with the other Blender Velvets addons. Open it as you would with any regular .zip file and extract them to some place of your choice (for example, at the Desktop).

Follow the detailed instructions on how to install Velvet Revolver at the How to install the addons section from the page How to configure Blender for video. Pay attention to the instructions related to FFMPEG. After that, define the framerate (FPS) of your project as described on the section How to start a project for video editing.