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September 29, 2014

EDL’s and CDL’s in a basic VFX Pipeline

This video is an overview of how EDL’s and CDL’s fit into a basic VFX pipeline.

EDL (Editors Decision List) is a file format that allows edited sequences to be transferred from one application to another. An EDL does not contain any footage, but rather a list of all edits made in a sequence. If you open an EDL file in a text editor, you’ll see that it’s simply meta-data telling the software you are opening it with, which video files to use, what the time in and time out of each clip is, and what effects have been added to the each clip. It also contains some other data referring to the sequence frame rate.

CDL’s (Colour Decision List) are similar to an EDL, however, instead of transferring sequences and information about where each clip must start and end, it contains data about colour changes that have been applied to the footage. It must be noted that a CDL can only store basic color adjustments, and not detailed adjustments like secondary colour correction.

We can thus say an EDL transfers edited sequences, and a CDL transfers the colour correction done on a sequence.

The generic VFX pipeline.

We all know media is generated by the camera. In this case I’m using a Arri Alexa, but this can be any camera.

The footage is then moved onto Hard Drive and verified, and often backed up to another set of drives or LTO.

This first port of call for the footage is the DIT station. Often this person or facility will also create dailies for review by the director. And Proxies for the editor.

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Now we know that raw footage is very large, and it’s unpractical to edit a feature film using the raw footage. I’ve illustrated the raw footage here using the “film reels” icons. So the raw footage needs to be converted to proxies or dailies for the editor to load the files into his editing machine. However, simply converting the footage to proxies is not enough:

It’s also very common for the director and DOP to create a “cinematic” look while shooting. It is thus the DIT’s responsibility to balance the image, and apply this LOOK to the dailies and to the proxies that is being edited so that the director and editor can work with the footage that already looks the way it was planned on set.

These proxies are then sent to the editors where the film will be cut.

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After the editor has edited the film, or partial sequences, the VFX Editor can prepare an EDL containing the shots that require VFX work. Now sending the footage from Edit to VFX is pointless at this stage, since the edit is using the proxy files that have already been pre-graded. – And as we know VFX needs to work with the ungraded, uncompressed files.

The VFX editor must thus send an EDL containing the VFX clips to the DIT. The DIT can then load the EDL into Resolve or Baselight and export only the parts needed of each shot in full quality, ungraded raw footage for VFX to begin their work.

At this point the VFX Editor will supply the VFX department with the same EDL given to the DIT. VFX can then use this EDL in their reviewing tools, to watch the shots they are working on in an editing timeline and sequence. More about this this workflow in another video.

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The DIT will also provide a CDL to VFX. Why? Well let’s discuss what VFX will be doing.

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Once a VFX shot is completed it must be rendered out to go back to editing. However, since the VFX department is working with the ungraded footage, and edit with the graded proxy footage, VFX must use the information in the CDL to apply the same grade that the DIT did, before sending a proxy file to the editor.

This shot then replaces the shot without VFX in the editing timeline and allows the director and editor to continue editing without seeing a difference between the renders from VFX and the DIT.

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Besides this proxy file, each VFX shot must also be rendered to match the RAW camera footage, exactly as supplied to VFX by the DIT with no CDL applied.

Pipeline_06557After the editor has completed the edit, and integrated the VFX shots, the film must be sent to be graded, finished and distributed. This process is often called the DI (Digital Intermediate) or Grading. The editor send a new EDL, containing the entire film’s editing choices, to the DI. This allows the edit to be opened in the grading suite.

However, the EDL does not contain any footage, so when grading, the RAW footage must be used in order to achieve the best quality product, and thus the DIT must supply the RAW footage needed to open the EDL, and VFX must supply the High Quality Renders that are the same as the Raw footage.

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All this footage, along with the sound design is then combined. The DIT will then supply the CDL used to create the look of the film. Since the DIT has pre-graded the film, it saves a lot of time during the final grade – which is a very costly process – final tweaks, and more specific effects are then applied before the film is packaged for distribution.

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And that is, in a nutshell how a VFX pipeline uses CDL’s and EDL’s to share data between facilities in order to facilitate an efficient and effective workflow. 

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Comments

  1. Joshua Selva

    Apparently, Final Cut Pro X is not longer producing EDL files, just XML.

    • WicusLab

      Hi Joshua,

      Yes, you are correct. EDL’s have been replaced in newer pipelines by XML’s (generally generated by FCPX and Premier) and AAF’s (Generated by AVID products such as Media Composer and Pro Tools). These file formats all replace a traditional EDL and are more advanced since they contain more information. An AAF can even contain video and audio embedded in the file which is not possible with an EDL or XML which only references external media.

  2. Kim Suponin

    Hi! Thank you for the very explanatory video/article. I got a question about the export phase to the DI though.

    When the DIT sends raw material to the DI: for example a red raw -sequence. What format does the VFX provide to the grader? I’m just wondering if the mismatch of formats and/or sequence names can cause trouble with managing the cuts and all the shots for the DI. Or is that part of combining raw material with the provided (high quality rendered) effects shots the so called conforming and is just a part of the pipeline?

    Thank you!

    • WicusLab

      The VFX would provide either a EXR or DPX Sequence to the grader. It’s important that the colorspace is not changed by VFX so that the file looks the same as the Red File for example. VFX also sends a quicktime proxy of this EXR/DPX to the edit, which is then used to conform.

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