Transferring non-linear audio and video when working with sound for picture is accomplished by the use of OMF or AAF files. So what are they, how are they created and how do you work with them in Pro Tools?
An OMF (Open Media Framework Interchange), which is also sometimes known as an OMFI, was developed by Avid in order that metadata and media data could be shared between both Mac OS and Windows; and different applications.
The AAF (Advanced Authoring Format) is a newer, open standard created in 2000 by a consortium of broadcasters and developers called the AAF Association (renamed in 2007, the Advanced Media Workflow Association). An AAF also enables metadata and media data to be shared across platforms and between different applications.
Metadata and Media Data
- This is the data that provides information on the length of each clip, the handle length, the position of the clip in the timeline, automation data (volume, pan), name of clip, etc.
- Media/Essence Data
- Includes audio, video, still images, graphics, text, animation, etc.
When creating either OMF or AAF files, the media can be embedded or externally referenced. Data that is included but not supported by the receiving application (e.g. Pro Tools) will be ignored. This typically includes effects added by other systems.
When exporting an OMF or AAF file with embedded media, the result is one large file containing both the metadata and all associated media files. Embedding media into a single file provides a convenient means to transferring data between systems, but it is important to note that a single OMF or AAF can be larger than 2GB only if no one individual media file contained within is larger than 2GB.
Embedded OMF / AAF file
Externally Referenced Media
When working with OMF or AAF files with externally referenced media you need to make sure that you transfer not only the OMF or AAF file, but also the corresponding folder of media. The OMF or AAF in this case will only include the metadata, but no media. It can be very useful to reference the media rather than embed it so as not to duplicate media unnecessarily, especially in a shared storage environment such as a post house.
Externally Referenced Media
Working with a Video Editor
When you are working on sound for picture it is likely that you will also have many new versions of the edit sent over as changes are made by the director. It is therefore good practice to make sure that the material that is sent over follows some “house rules” so that everything runs as smoothly as possible.
Firstly their timeline should be set to 48 kHz / 24-bit audio to maintain the highest quality and dynamic range from their project.
Next is maintaining sync. By default the video timeline starts with a timecode of 00:00:00:00 (hours, minutes, seconds, frames). However, as a means of making sure that the data that is transferred appears in the correct place, it is normal to add additional clips for sync. It is standard that when editing film, the start of the video starts at 01:00:00:00 and if editing a television show 10:00:00:00. I will concentrate on working on film here, but feel free to adjust the timecode accordingly for television.
‘2 pop’ Video – punch, Audio – 1kHz -20dB sinewave
When referring to the start of the video, we refer to the First Frame of Action (FFOA), with the end of the film being the Last Frame of Action (LFOA). Exactly 2 seconds before the FFOA and 2 seconds after the LFOA there should be a ‘2 pop’. This consists of a punch in the video lasting exactly 1 frame; and a 1kHz, -20dB sinewave also lasting exactly 1 frame in every single audio track. The punch can be created easily as a white circle in the centre of a black frame. So in the case of film, this would occur at 00:59:58:00 which is 2 seconds before the FFOA at 01:00:00:00.
Countdown clock and project information
Leading into the first ‘2 pop’ is a countdown clock, ideally with information on the project being transferred. This should last between 10 – 45 seconds, to give enough time to read any associated information and have a visual line up of where the ‘2 pop’ will be. When this reaches 3 seconds to go, this will go black for 1 second.
HD Bars and Tone (with Timecode overlay)
It is also customary to have Bars and Tone prior to the countdown clock in order to provide reference for both colour and audio level.
Placed over the top of all of this (and crucial for any future changes in the edit) will be burnt-in timecode.
In order to speed up the process of editing and mixing the sound in Pro Tools, it is also important to convey to the video editor that a well laid out timeline can save a lot of time. Making sure that the tracks are named and audio clips are on the correct track. A track list is also often sent along with any additional notes.
The video editor will then provide an exported video reference file containing all of these elements and their current sound mix, along with the exported OMF or AAF file (and related media if necessary).
Video Editor’s Timeline Overview
Importing into Pro Tools
File – Import Session Data
Two options are available to import OMF/AAF files into Pro Tools
- Open OMF/AAF as a new session
- Choose File – Open Session
- Select the OMF or AAF file
- Keep or adjust the Session Parameters (File type, Bit Depth, Sample Rate)
- Configure Import Session Data
- Import OMF/AAF into current Pro Tools session, especially useful when using Pro Tools templates or conforming a new edit
- Choose File – Import – Session Data
- Configure Import Session Data
It is worth noting that an OMF or AAF that contains embedded video are not supported by Pro Tools and cannot be imported.
Import Session Data – Source Properties
The Source Properties section displays information about the format of the data to be imported into the session including:
- Sequence Name
- Name of sequence in source editing system
- File Type
- OMF, AAF, Pro Tools session
- Start Time
- Timecode start time of sequence
- Timecode format
- Frame rate of incoming timecode
- Audio Bit Depth(s)
- Typically 24 Bit, but sequences sometimes have multiple Bit Depths associated with them
- Audio Sample Rate(s)
- Typically 48 kHz, but sequences sometimes have multiple sample rates associated with them. This will be converted to the session sample rate on import
- Audio File Type(s)
- Typically Embedded, but sequences can have multiple file types associated with them
- Video Frame Rate
- The frame rate of associated video
Import Session Data – Media Options
The Audio Media Options tell Pro Tools what to do with the source media when importing an OMF, AAF or Pro Tools session.
- Link to source media (where possible)
- Tells Pro Tools to refer to as many of the original media files as possible. Pro Tools will not copy or make any duplicates of media unless required.
- Copy from source media
- Copies referenced audio to session Audio Files folder.
- Also allows sample rate conversion during copying.
- Consolidate from source media
- Copies referenced audio to session Audio Files folder but removes all unused areas of media in copies.
- Handle size specifies amount of additional material to keep on each clip.
- Also allows sample rate conversion during copying
- Force to target session format
- Converts source media to session audio file format if source media differs from session file format
The Video Media Options tell Pro Tools what to do with any related video material referenced by the OMF, AAF or Pro Tools session.
- Link to source media
- Tells Pro Tools to refer to source video files. Pro Tools will not copy or duplicate source video
- Copy from source media
- Copies all video files from source video to specified location.
- Useful to indicate a video drive to import to in order for Pro Tools to efficiently playback session.
- Import as offline satellite media (Pro Tools HD software only)
- Imports a video track with offline media for use when working with a Video Satellite system. Useful to navigate scenes and edits as cuts and clip names are visible in Pro Tools
Import Session Data – Timecode Mapping Options
Pro Tools allows you to map the timecode of the imported tracks to the current session.
- Maintain absolute timecode values
- Available only if the imported timecode is the same or greater than the current session. Places imported media at the timecode where they were located in the source sequence.
- If your current session starts at 00:00:00:00 and the imported timecode starts at 01:00:00:00, then all of the imported media will be placed 1 hour down the timeline.
- Maintain relative timecode values
- Places imported media with the same offset from the session start as they have in the original sequence
- If your current session starts at 00:00:00:00 and the imported timecode starts at 01:00:00:00, then the imported media will in fact be placed to start at 00:00:00:00.
- Map start timecode to
- Allows you to remap the original sequence timecode to a timecode of your choice
- If the imported sequence has a timecode of 01:00:00:00 and you need it to be placed at 02:30:00:00, then you can remap the start to this point
- Adjust session start time to match source start time
- The last option allows you to change the start timecode of your session to the incoming timecode. Particularly useful if you haven’t set this up in Session Setup
In addition to the Timecode Mapping Options you can offset the incoming tracks with the Track Offset Options, which allows you to adjust for different timescales (Bars|Beats, Minutes:Seconds, Timecode, Feet+Frames or Samples).
When importing an OMF, AAF or Pro Tools session you have the option to map the imported tracks to New Tracks or to existing tracks within your session. It is important to note the following options available
- Import – Replace existing playlists
- The main playlist of the existing track is replaced with the main playlist of the imported track.
- Selecting this option but selecting not to import the imported tracks attributes imports the audio but retains any mixer settings for that track
- Import – Overlay new on existing playlists
- Imported data is merged with data that already exists on that track. So existing material will be replaced by the imported data if it overlaps, but remain on the track if not.
- Do Not Import
- This option does not import the main playlist but instead imports any selected attributes in the Track Data to Import list.
- No audio is imported.
Once all of the options have been chosen you are ready to import into Pro Tools to start working on the sound.
Session Sound Mix – Newly imported OMF / AAF
It is a good idea now to duplicate these tracks and then choose Hide and Make Inactive, so that you have the original material to go back to if you need to.
Key to making sure that you work efficiently with OMF and AAF files is communication with the rest of the team on that project. Setting out what you require from them and how a project will be delivered will help to speed up the process. Naming of tracks and organization of media on the source side will also aid in this.