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SMPTE frame rates

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Top 200 Contributor
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MWeeks728 posted on 04-25-2012 6:02 PM

If I am using an external SMPTE source and speed up (double) the frame rate from that source would all the cues in the event list execute faster and have shorter times?

M Weeks 

IATSE 728

GIO 2K

Current show - Castle

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Top 10 Contributor
1,034 Posts

No, it wouldn't speed up the list. Do you want to speed up the list? I don't think there is currently a way to do that.

Dan Duffy Eos Software Developer

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I want to speed up the list.
I've switched to MIDI Time Code that is being generated from Logic Pro 9 Playing back a music track for a video. 

DP wants to shoot at 24FPS and at 48FPS as well. At regular speed the MIDI time code is generated and triggers the events on my list correctly. When we double the speed of the MIDI time code to support shooting twice as fast the console takes the initial timing information (first few frames) and then rapidly gets out of sync as the midi source is running twice as fast. I have tried disabling the internal timing source to see if that would help.

The thought is to vary the Rate as needed once the midi triggers have been placed on the audio track.

Basically I want the console to be a constant slave to an external MIDI source regardless of the speed of the source.

 

M Weeks 

IATSE 728

GIO 2K

Current show - Castle

Top 150 Contributor
64 Posts

 

SMPTE and MIDI Time Code are designed to synchronize the clocks of devices running in real time.

A specific frame is represented in Hours:Minutes:Seconds:Frames.

Changing the frame rate does not change the speed. It just increases the number of steps (frames) per second.

 

What device or software are you using to speed up the time code?

Top 200 Contributor
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I think I have muddied the waters by referring to frame rates.

The MIDI frame rates are staying constant on the console and MIDI source at 30 Frames per Second.

The Camera being used to shoot the video will be using different frame rates to achieve different effects.

We are using Pro Logic for playback.

Pro Logic allows for playback to occur at different speeds and changes the speed of the MIDI time code it generates accordingly.

At normal playback speed the console syncs with the MIDI source seamlessly and triggers the events at the right times.  

When playback happens twice as fast - Pro Logic is generates a time code where one second of elapsed time has two seconds of audio track, the console syncs with the MIDI source at the start but rapidly falls behind.

 

What I am trying to do is to have specific points of an audio track to trigger events on the console. If every 2 seconds at normal audio playback speed the [GO] is pressed when I double the audio playback speed the [GO] should occur every 1 second.  

M Weeks 

IATSE 728

GIO 2K

Current show - Castle

Top 50 Contributor
187 Posts
I don't know if this will completely fix your problem, but have you tried changing the rate of the cue list? That will at least make the cues play back twice as fast.

 

Jon Goss

Top 200 Contributor
50 Posts

I'll try that in the morning and see what happens...

 

The issue is using the MIDI source to trigger events. It appears that the console and the MIDI source sync right up but if the MIDI source is faster then the consoles clock the two get out of sync. 

it would be nice to have the ability to sync the console with off-speed sources.

M Weeks 

IATSE 728

GIO 2K

Current show - Castle

Top 10 Contributor
1,421 Posts

Have you looked at the actual MTC that is being output?

I'm unconvinced that this kind of use is actually possible with the MTC standard.
- See http://en.wikipedia.org/wiki/MIDI_timecode for some background info.

From a spec summary linked from that page:

"During fast forward or rewind (ie, shuttle) modes, the master should not continuously send Quarter Frame messages, but rather, send Full Frame messages at regular intervals."

A Full Frame message is also a "pause" command, quarter-frame messages are needed to let the device know time is really passing (this is to avoid triggering events when shuttling to a new place in the tape).

My guess is that it is not sending the continuous stream of quarter-frames at 'double time', it's doing something else instead.

Keep on trying till you run out of cake.

ETC Field Service, London

Top 200 Contributor
50 Posts

Read the wiki...drank some coffee and read the wiki again. 

So If I understand this at normal speeds-

MTC sends one full frame of data at the start to sync devices and then sends 1/4 frame data streams that devices use to increment the time count.

 

"When there is a jump in the time code, a single full time code is sent to synchronize attached equipment."

So my guess is because we are not playing back at normal speeds the software is out putting full frame MTC messages but the ION is not continuosly resyncing with the output device it is starting and running time on it's own.

Going to look on the audio side to see if we can set it to output quarter frame messages at higher speeds.

So if MTC isn't the way to go with this how can I sync a console to an external source and have the ability to vary the playback rate to conform with different shutter speeds?

M Weeks 

IATSE 728

GIO 2K

Current show - Castle

Top 200 Contributor
50 Posts

Found an interesting thing when editing the time of an event-

 

event time is hr:min:sec:frame

event x [time] + #

this syntax will add time - 1 frame.

if you want to add one frame you need to type-

event x [time] +2

if you want to move it four frames back you type-

event x [time] + 5

 

BUT 

 

if you want to move this event in the other direction

event x [time] - #

to pull an event up by 6 frames you would type-

event x [time] - 6 

and this would pull the event up by six frames.

M Weeks 

IATSE 728

GIO 2K

Current show - Castle

Top 10 Contributor
1,034 Posts

Thanks, this last defect about adding or subtracting a SMPTE time being off by 1 frame is fixed in 1.9.11.

Dan Duffy Eos Software Developer

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