We had a question in from community member Daniel Cabrera in Podcast 239 as he was looking to move to an Apollo interface but was concerned about video sync not having a Sync HD I/O on his potential new system. Daniel asked...
Firstly, thank you very much for your time. I am a sound editor and dialogue editor and I am planning to buy a new interface for Pro Tools 12, and I am looking at an Apollo 8 quad instead of an Avid HD Omni with an HD Native card, because I really prefer sound of UA, but recently I read Pro Tools only runs video properly with Avid interfaces and an HD Sync I/O, but I have my doubts if it's totally right, and I would be pleased to hear from you and your thoughts. Thanks for your kindness. Daniel.
So we asked our resident post production expert Alan Sallabank for his take on this issue as Alan doesn't have Avid HD hardware, he uses Pro Tools HD software but uses an RME interface in his studio.
My own view is that as long as you're not using lossy video codecs (such as H264), and you're not locking the Pro Tools to another system, it can run well within tolerances on internal sync. SyncOne2 tests on "stand alone" Windows 10 Pro Tools 12HD systems using Blackmagic digital output only (HDMI & HD-SDI) hardware, running DnX36HD media, show excellent consistency. For Mac systems, evidence seems to point at AJA being the better hardware in this aspect, for use with the AVE.
Some editors claim to be able to see a quarter frame drift between frames. While I'm not personally able to identify it that accurately, it can make a big difference to the "feel" of an ADR fit. If you are convinced that inter-frame sync drift is noticeable to you, then some higher end video cards from Blackmagic and AJA have video reference inputs. If you get a sync pulse generator that can output both Tri-Level Syncs (for working in the HD frame rates) and Word Clock, simultaneously clocked from the same source, then you can lock your Pro Tools to word clock through your Apollo, and your video card to TLS.
One thing that is known to be a very good idea, is to have your video media playing off a fast SSD - so for a Mac, a Thunderbolt external, or a SATA3 or PCIe connected internal SSD drive. This has been proved to substantially improve video playback reliability and performance, and completely stands to reason - you are giving the highest possible bandwidth of data to the video playback.
If you would like to know more on why there is a need for sync pulse generators and Tri Levels Syncs then scroll down the article to the History section...
To run Avid Video Satellite you need to have a SyncHD box and a HD Native or HDX card, for each machine run in sync. You of course also need Pro Tools HD. This can get very costly.
Not only can Video Slave 2 playback video remotely, it can also overlay timecode, ADR cues, streamers and imported script prompts, and you can even choose different overlays for different video devices, meaning for instance that your ADR talent could watch the output with all the cues, while the ADR supervisor watches sync on an uncluttered screen.
Video Slave 3 - What's New?
Video Slave 3 works with all major DAWs including Pro Tools, Logic Pro X, Nuendo, Cubase and Studio One - or any other device that can generate midi timecode as a source. Video Slave 3 can be used either on a wired MIDI connection or through network MIDI.
Same Solid Performance, New Features
The revised sync engine provides stunningly fast locking times and tight sync guaranteed: in many cases it's better than using the video engine built into the DAW. Here are the new features at a glance...
- Upgraded video playback engine, including AJA device support
- Improved Overlays
- New ADR workflows, including Pro Tools remote control
- Pro Audio interface support
- Custom movie export - export your movies with overlays burnt in
- Perpetual and subscription license options
Why Is This All So Important?
For the younger members of the community, you may be wondering what all the fuss is all about so Alan Sallabank gives us a little background and history.
This issue stems from the days of locking linear tape machines together. All DAW systems and tape machines have an inbuilt crystal driven sync generator. It’s the same basic clock that keeps your watch accurate. There can however be minute variations in the absolute speed that these crystals generate, which even though they’re minute, can cause sync drift between machines. It’s why your watch can run fast or slow compared to the nuclear clock and will need adjusting back in time or 're-syncing' over time.
Multi machine and multi studio facilities have what’s known as “Station Syncs”, which is a master Sync Pulse Generator. This generates video syncs (and often word clock), which is fed to every machine in the facility. This means that any studio can connect to any machine in the building, and still run at the same absolute speed, as dictated by the Station Syncs generated by the master Sync Pulse Generator.
Why is this important? This is all down to the method used to lock machines together, be they non-linear such as Pro Tools, or linear, such as a tape machine.
Use A Synchroniser
Machines are locked together using a Synchroniser, which generates a master timecode timeline, and then controls the machines that are physically connected to it using RS422 9-pin interfaces (or even in the older days proprietary interfaces). It also generates a master linear timecode timeline, for feeding to machines that use their own in built synchronisers to lock to incoming timecode.
The synchroniser will control the tape machines and use what’s known as “slew” (varispeed), to match the tape machine’s timecode to the timeline. Once the synchroniser is happy that the machine is in sync, according to the frame edges of the timecode, it then does an operation known as “releasing to syncs”. It releases slew control and tells the machine to play, at the speed dictated by the station syncs.
From this point it then just keeps an eye on the timecode coming from the slave machine, and if the frame edges start to drift out of sync, will attempt to re-slew it back into sync. If this slave machine happens to be recording at the time and the synchroniser attempts to re-slew it, if it’s analogue you will get a “wow” in your recording, but if it’s digital it will either stop completely or corrupt the recording.
When a machine is following external timecode, the in-built synchroniser does the same thing, even if it’s non-linear.
Possible Issues With A Single Pro Tools System
In a single Pro Tools system, all hardware and software should be locked to the same crystal generated reference, so should all run at the same absolute speed when released to syncs. One way this can be broken is by locking your Pro Tools to external word clock or digital input fed from another device, but not having your video playback referenced to the same external sync source.
Taking everything into consideration, it is our view that you can use internal sync video without the need for HD hardware very effectively, especially on a single stand alone system.
- You should NOT use very lossy codecs like H264 for video playback with Pro Tools.
- We recommend using the Avid DnX36 codecs as they put very little load on your system
- Put you video media on a separate hard drive, ideally an SSD drive.
- Try not to put your video files on the same drive as your Pro Tools session.
- We suggest you consider using Video Slave 3 from Non Lethal Applications, either on the same machine or on a separate computer as a very versatile and flexible solution.