Abstract
Many reviews, particularly between vendor and production company end up transcoding the source media to a movie format for review. Even after the movie file generation the production company may rename the file to match their own conventions (if they dont transcode it again). Adding metadata to these transcoded files (and provide recommendations on how to carry any metadata through additional transcoding sessions) could help then translate any notes, or annotations back to the source media.
Secondarily it would be good to make recommendations for transcoding for review. During reviews, its common to single frame forward and backwards, color fidelity is often critical to the review process, so we need to know that the resulting media isnt making any color adjustments (this was an issue with h264 in quicktime for a while).
At this point its not clear if this is just a standards process, or if code will need to be developed.
Metadata Standards
Media definition
These fields are for transcoded media, for original frame sequences it shouldn't be necessary. Metadata that should exist in the media file could include:
| First Frame, Last Frame | int | Encoding to movie files typically looses the start frame, making it a pain to identify which frame you are looking at. We could look at doing this with timecode, but sometimes you want both timecode and a frame number. |
| Source filename | string | Something to track where the encoded media came from. |
| Source frame rate | float | If you are reviewing a proxy, but still want to remap back to the source frame, knowing the source frame rate is required (DO WE NEED THIS AND LAST FRAME?) – useful for high-frame rate media, e.g. 120 fps - (MIGHT MAKE SENSE AS A STRING TO HANDLE 59.94 better?) |
| Watermarking? | String | Document what sort of watermarking has been applied? - invisible, burnin? |
Review definition
Metadata that should exist in the file.
| Source ID | string | A unique ID for the company generating the media that can be used to get back to the original media. The main use of this is if the filename changes as it goes through different company pipelines. |
| Source Entity | string | Identifies the shot, asset or entity. Potentially useful as a burn-in. |
| Source sub entity | string | This would be the way to identify the media within the source entity without versions. e.g. lets say I have a filepath /shows/spy01/bat001/pix/rnd/precomp_v001/precomp_v001.0001.exr spy01 = SHOW bat001 = SHOT = Source Entity precomp = Source subentity This would be used by an asset management system to group versions, without having to guess what the versioning system is. |
| source sub entity version | float | Version ID for sub-entity. |
| Task | string | Taskname if known at creation - |
| colorspace | string | Many file-formats do already have options for color spaces, but certainly for internal reviews facilities may decide to encode to a non-standard color space. For media that is crossing facilities we should stick to known embedded colorspaces, and allow existing tools to remap where necessary. |
| date authored | string | The latest date of the original authored content. This would be carried through any transcoding, so we dont end up with the transcoded timestamps. |
For doing external reviews (vendor passing media to production company) you may have additional metadata that needs to be passed with the media for review, this would typically be in an excel file (See VES Delivery Specification) with the following columns:
| Date Submitted | date string | repeated on each line for cases where the resulting excel sheet is merged. |
| Vendor | string | Vendor name, repeated on each line for cases where the resulting excel sheet is merged. |
| Filename | string | The filename that is being shipped to be reviewed. |
| Source ID | string | Used to map the following fields to the actual media. |
| review task name | string | The reviewing company may have their own task names, which could be "comp", "anim" |
| Review for | string | Notes on why the media is being reviewed, e.g. For Final, For Feedback, WIP. |
| Notes | string | Notes for the reviewer, so they know what they should be commenting on. |
NOTE, some or all of these fields may also make sense embedded.
Implementation
Use existing metadata values where possible, and fall back on XMP where not.
https://www.adobe.com/devnet/xmp.html
or
https://wiki.multimedia.cx/index.php/FFmpeg_Metadata
Annotations and Notes
The other area that common specifications could be defined is how annotations and notes could be sent back to the vendor, in a format that is ready for ingest into the tracking system.
Encoding standards
FFMPEG
Can we define ffmpeg standards for playback, including color space conversion. The default color space for ffmpeg is bt601, which is not typically what we are all using any more, but there are a number of conversion options that we should be considering. Its fairly typical to see the
-vf "colormatrix=bt601:bt709" flag in conversions. This is an 8-bit color space conversion, there is apparently a better option, see: https://trac.ffmpeg.org/wiki/colorspace
Shotgun transcoding: https://support.shotgunsoftware.com/hc/en-us/articles/219030418-Do-it-yourself-DIY-transcoding
Syncsketch points to this: https://cms.eas.ualberta.ca/dif/case-studies-tutorials/ffmpeg-convert-image-sequence-into-movie/
Reference "Dailies script" https://github.com/jedypod/generate-dailies
EXR
RV has notes on performance here - https://support.shotgunsoftware.com/hc/en-us/articles/219042268-Optimizing-RV-Playback-Performance