delay-free recording at DVinfo.net

Gints Klimanis · September 5th, 2003, 05:06 PM

We all have experienced the lost and extraneous footage that result from the tape startup delay after pressing the Record button. I'd like to suggest to manufacturers to add a recording buffer that would always record the last several seconds of material and print the material to tape starting at the time of the Record button press. The pre-buffer amount could be programmable, as well as an audio fade in time.

Jeff Donald · September 5th, 2003, 05:29 PM

The problem is the audio is out of sync with the video on recording buffers like you describe. Even the expensive cameras don't audio features like you're describing.

Gints Klimanis · September 5th, 2003, 05:34 PM

The buffer would be placed after all of the DV encoding stuff and would buffer the digital bitstream that is sent to the tape. At that point, the audio/video would be in sync. I'd love to see this buffering feature. It would eliminate all of those seconds of useless preroll in *every* shot.

Jeff Donald · September 5th, 2003, 05:38 PM

Are you referring to the pre-roll that video cameras do? Sorry missed that in your last post. The pre-roll is necessary to get the rotating upper drum assembly (heads) up to speed. With audio if parts aren't moving at exactly the right speed the pitch is off. If the speed of video tape is not perfect your video is unusable.

Once solid state recording becomes reality a buffering system like you describe would be possible.

Gints Klimanis · September 5th, 2003, 06:02 PM

Jeff,

Yeah. While the tape is getting up to speed, the buffer would hold the video data recorded from the time the start button is pressed. Then, the camera would dump that data onto the tape and continue to record. I don't think a fully solid-state recording
system is necessary. DV25 is 25 MBits/second, or about 3 MBytes/second. A 16 MByte buffer would handle five seconds of data.

Jeff Donald · September 5th, 2003, 06:21 PM

There would always be a delay of 5 seconds. When I shot news the big Betacams etc. all have confidence heads. Confidence heads are playback heads immediately after the record heads. They allow the camera operator to see in the viewfinder what is actually being recorded to tape, dropouts and all. The consensus is that the ability to view the recorded material in real time is of the utmost importance. Other wise you could have a head clog and not be recording anything. You wouldn't know until you got back to the station (worst case scenario).

Mike Rehmus · September 5th, 2003, 07:05 PM

I believe the disk recorders that are designed to be plugged into the cameras do indeed have about an eight second prerecord feature. Only costs $1200-$2200 to play with one of those.

Gints Klimanis · September 5th, 2003, 07:06 PM

It doesn't matter if the tape is recording 5 seconds behind real-time. All other monitoring would still be done in real-time.

This is what we do today:
1) setup scene
2) press Record
3) wait 5-10 seconds
4) signal "Go"

Step 3) is extraneous. We are used to this, and it doesn't have to be this way. In additional to dynamic recording situations where you don't really want to record the entire event and press Record/Stop often, buffering is key. Also, there are times when you realize that you haven't pushed the Record button properly or at all. Desirable footage is lost. This doesn't have to happen.

In the cases needing real-time "confidence heads", turn off the buffering or minimize it. Even with the buffering, you can still monitor delayed material for recording problems such as head clogs. If you have a a bad head, the camera is shot anyway, right ?

>The consensus is that the ability to view the recorded material in real time is of the utmost importance

Do the majority of camcorder products agree with your consensus?

Jeff Donald · September 5th, 2003, 07:57 PM

Quote:

>The consensus is that the ability to view the recorded material in real time is of the utmost importance

Do the majority of camcorder products agree with your consensus?

At the professional level, yes. It's a standard feature. Prosumer cameras have neither real time, confidence viewing, and would only get buffering system after it trickles down from pro systems.

Confidence heads allow you to monitor for more than head clogs. Dropouts can be observed and scenes reshot if necessary. It would be extremely difficult to view an event as it unfolds in one eye and watch a delayed version with the other. How could you focus etc. You focus your lens or adjust the audio and it's 5 seconds to see or hear your changes. I could see that causing big problems for people.

As you point out, a dual system could exists, but that would only add to the expense. The cost for implementing a recording process, such as you purpose, will eventually come down. If the market place truly feels a need for instantaneous recording, I'm sure the manufactures will respond. In the meantime i think Mike's suggestion of the hard disk recorders may be your best bet.

Gints Klimanis · September 5th, 2003, 09:12 PM

>would only get buffering system after it trickles down from pro >systems.

All consumer/prosumer system features aren't a subset of pro system features. Since Pros apparently prefer the absence of this feature, the low end will drive the emergence of bitstream buffering.

>As you point out, a dual system could exists, but that would >only add to the expense. The cost for implementing a recording >process, such as you purpose, will eventually come down.

The actual cost is probably small. Increasing system memory by an additional 16 MBytes and a path from the DV encoder are probably all that is needed in hardware.

> In the meantime i think Mike's suggestion of the hard disk >recorders may be your best bet.

It looks like flash cards/microdrives are the current path, with capacities approaching 4 GBytes.

Jeff Donald · September 6th, 2003, 04:15 AM

I don't think micro drives are meant for continuous duty. Some type of flash memory would be more practical and reliable.

How would the audio work? If I monitor the actual recording everything is delayed 5 seconds. If I see the VU meter is too high (live event) and I make adjustments, do I get the changes now or in 5 seconds? Do the VU's show real time or a 5 second delay?

Mike Rehmus · September 6th, 2003, 12:14 PM

Ah but you see you can apply the level adjustments to the audio stream at the back end of the 5 second delay but be able to watch and react to the need at the front end of the delay. The system will just delay the adjustment so that it matches in time, the signal.

The VU reads at the front (real time) end of the delay.

That means you could also adjust the video as well although obviously, that could not apply to lens- and optical block-specific adjustments. One could change the way the DSP processes the video.

Jeff Donald · September 6th, 2003, 02:23 PM

Seems like it's getting way too complicated for the minor benefits to be gained. Dual signal paths would just add to the cost. Adding signal processing at different points in the signal creates additional timing errors. Is all this worth it to have an instant recording instead of waiting 3 to 5 seconds?

Mike Rehmus · September 6th, 2003, 02:52 PM

It is one of those optional extras that the camera manufacturers need to consider in their next round of cameras.

I'd pay more for these options on PD150 and DSR-300 level chassis:

- Continuously variable frame rate from 1 to 120 fps
- Internal waveform monitor viewable in the viewfinder
- Pre-roll buffer
- High-quality microphone pre-amps
- Constant readout of focus distance including DOF info, zoom, aperature, gain (audio and video) and shutter speed.
- Stepless aperature, gain, and shutter speed settings with clear-scan capability (DSR-300 already has stepless aperature)
- High-quality audio compressor like the DBx Mini-Comp
- Expanded dynamic range optical block.

But not everyone would. So I'd like an options slot. Probably like a PCMCIA card slot.

September 5th, 2003, 05:06 PM	#1
Gints Klimanis Inner Circle Join Date: Jun 2003 Location: San Jose, CA Posts: 2,222	delay-free recording We all have experienced the lost and extraneous footage that result from the tape startup delay after pressing the Record button. I'd like to suggest to manufacturers to add a recording buffer that would always record the last several seconds of material and print the material to tape starting at the time of the Record button press. The pre-buffer amount could be programmable, as well as an audio fade in time.

September 5th, 2003, 05:29 PM	#2
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	The problem is the audio is out of sync with the video on recording buffers like you describe. Even the expensive cameras don't audio features like you're describing. __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

September 5th, 2003, 05:38 PM	#4
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	Are you referring to the pre-roll that video cameras do? Sorry missed that in your last post. The pre-roll is necessary to get the rotating upper drum assembly (heads) up to speed. With audio if parts aren't moving at exactly the right speed the pitch is off. If the speed of video tape is not perfect your video is unusable. Once solid state recording becomes reality a buffering system like you describe would be possible. __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

September 5th, 2003, 06:21 PM	#6
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	There would always be a delay of 5 seconds. When I shot news the big Betacams etc. all have confidence heads. Confidence heads are playback heads immediately after the record heads. They allow the camera operator to see in the viewfinder what is actually being recorded to tape, dropouts and all. The consensus is that the ability to view the recorded material in real time is of the utmost importance. Other wise you could have a head clog and not be recording anything. You wouldn't know until you got back to the station (worst case scenario). __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

September 5th, 2003, 07:05 PM	#7
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	I believe the disk recorders that are designed to be plugged into the cameras do indeed have about an eight second prerecord feature. Only costs $1200-$2200 to play with one of those. __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!

September 5th, 2003, 05:34 PM	#3
Gints Klimanis Inner Circle Join Date: Jun 2003 Location: San Jose, CA Posts: 2,222	The buffer would be placed after all of the DV encoding stuff and would buffer the digital bitstream that is sent to the tape. At that point, the audio/video would be in sync. I'd love to see this buffering feature. It would eliminate all of those seconds of useless preroll in every shot.

September 5th, 2003, 06:02 PM	#5
Gints Klimanis Inner Circle Join Date: Jun 2003 Location: San Jose, CA Posts: 2,222	Jeff, Yeah. While the tape is getting up to speed, the buffer would hold the video data recorded from the time the start button is pressed. Then, the camera would dump that data onto the tape and continue to record. I don't think a fully solid-state recording system is necessary. DV25 is 25 MBits/second, or about 3 MBytes/second. A 16 MByte buffer would handle five seconds of data.

September 5th, 2003, 07:06 PM	#8
Gints Klimanis Inner Circle Join Date: Jun 2003 Location: San Jose, CA Posts: 2,222	It doesn't matter if the tape is recording 5 seconds behind real-time. All other monitoring would still be done in real-time. This is what we do today: 1) setup scene 2) press Record 3) wait 5-10 seconds 4) signal "Go" Step 3) is extraneous. We are used to this, and it doesn't have to be this way. In additional to dynamic recording situations where you don't really want to record the entire event and press Record/Stop often, buffering is key. Also, there are times when you realize that you haven't pushed the Record button properly or at all. Desirable footage is lost. This doesn't have to happen. In the cases needing real-time "confidence heads", turn off the buffering or minimize it. Even with the buffering, you can still monitor delayed material for recording problems such as head clogs. If you have a a bad head, the camera is shot anyway, right ? >The consensus is that the ability to view the recorded material in real time is of the utmost importance Do the majority of camcorder products agree with your consensus?

September 5th, 2003, 09:12 PM	#10
Gints Klimanis Inner Circle Join Date: Jun 2003 Location: San Jose, CA Posts: 2,222	>would only get buffering system after it trickles down from pro >systems. All consumer/prosumer system features aren't a subset of pro system features. Since Pros apparently prefer the absence of this feature, the low end will drive the emergence of bitstream buffering. >As you point out, a dual system could exists, but that would >only add to the expense. The cost for implementing a recording >process, such as you purpose, will eventually come down. The actual cost is probably small. Increasing system memory by an additional 16 MBytes and a path from the DV encoder are probably all that is needed in hardware. > In the meantime i think Mike's suggestion of the hard disk >recorders may be your best bet. It looks like flash cards/microdrives are the current path, with capacities approaching 4 GBytes.

September 6th, 2003, 04:15 AM	#11
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	I don't think micro drives are meant for continuous duty. Some type of flash memory would be more practical and reliable. How would the audio work? If I monitor the actual recording everything is delayed 5 seconds. If I see the VU meter is too high (live event) and I make adjustments, do I get the changes now or in 5 seconds? Do the VU's show real time or a 5 second delay? __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

September 6th, 2003, 12:14 PM	#12
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	Ah but you see you can apply the level adjustments to the audio stream at the back end of the 5 second delay but be able to watch and react to the need at the front end of the delay. The system will just delay the adjustment so that it matches in time, the signal. The VU reads at the front (real time) end of the delay. That means you could also adjust the video as well although obviously, that could not apply to lens- and optical block-specific adjustments. One could change the way the DSP processes the video. __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!

September 6th, 2003, 02:23 PM	#13
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	Seems like it's getting way too complicated for the minor benefits to be gained. Dual signal paths would just add to the cost. Adding signal processing at different points in the signal creates additional timing errors. Is all this worth it to have an instant recording instead of waiting 3 to 5 seconds? __________________ Jeff Donald Carpe Diem Search DVinfo.net for quick answers \| Where to Buy? From the best in the business: DVinfo.net sponsors

September 6th, 2003, 02:52 PM	#14
Mike Rehmus Wrangler Join Date: May 2002 Location: Vallejo, California Posts: 4,049	It is one of those optional extras that the camera manufacturers need to consider in their next round of cameras. I'd pay more for these options on PD150 and DSR-300 level chassis: - Continuously variable frame rate from 1 to 120 fps - Internal waveform monitor viewable in the viewfinder - Pre-roll buffer - High-quality microphone pre-amps - Constant readout of focus distance including DOF info, zoom, aperature, gain (audio and video) and shutter speed. - Stepless aperature, gain, and shutter speed settings with clear-scan capability (DSR-300 already has stepless aperature) - High-quality audio compressor like the DBx Mini-Comp - Expanded dynamic range optical block. But not everyone would. So I'd like an options slot. Probably like a PCMCIA card slot. __________________ Mike Rehmus Hey, I can see the carrot at the end of the tunnel!