HMC150 - Terrible problems with strobe lights!

R

Rikki

Well-known member
Just shot a dance event that used a lot of strobe lights and this was the result :

badavchd.jpg


Here's a link to the footage : http://www.strathycruise.com/pics/badavchd.jpg.mp4

The screen grab is from the original MTS file, checked in both VLC player and Sony Vegas plus it looks just as bad when NeoScene converted as expected.

My Canon HV20 managed to handle this type of shooting perfectly with HDV so why does the pro grade AVCCAM not manage? :(
 
Did this occur in the entire footage the entire shoot, or just in that short span?

Can you upload a native .mts sample that exhibits this issue? You can cut a small segment with tsmuxer for example
 
Happens pretty much every time there is a blast of strobe.

I dont have tsmuxer, can you give me a link to it and quick note on how to chop a bit out ?

Thanks

Rikki
 
So the entire footage has this? Because there are some strobe frames that do not exhibit this behaviour on your re-encoded footage.

To me it looks like a decoding issue, perhaps a bad keyframe (and subsequent I/P frames for some GOP's not all of them). I just want to verify on the native footage. It's tough to tell on a re-encoded sample.

http://www.videohelp.com/tools/tsMuxeR

Direct link:
http://www.videohelp.com/download/tsMuxeR_1.10.6.zip

Push add in the 1st tab to load the .mts file, go the the split and cut tab, checkmark enable cutting and enter the start/end points. Either the ts or m2ts radio button can be checked, push start muxing. There are free hosting site alternative too e.g. mediafire.com
 
I think that type of environment is asking a lot from a compression system that is designed to use long GOP. You may need to use a much higher bit rate and intra frame rather than inter-frame compression - which of course is not available on the HMC. Some cameras cost more money for a reason :)

AVCHD is designed to store the differences between frames much more often than it stores complete frames (keyframes) - and uses a lower bit rate than the HV20. When the strobe turns on or off there are massive changes to the scene that really require a full keyframe because you simply don't have enough bandwidth to store the 'differences' from the last frame. Fast strobes are going to expose serious limitations in inter-frame compression systems.
 
Exact said:
I think that type of environment is asking a lot from a compression system that is designed to use long GOP. You may need to use a much higher bit rate and intra frame rather than inter-frame compression - which of course is not available on the HMC. Some cameras cost more money for a reason :) AVCHD is designed to store the differences between frames much more often than it stores complete frames (keyframes) - and uses a lower bit rate than the HV20.
Click to expand...
This is irrelevant as AVCHD is supposed to be twice effective, and in PH mode it can reach 24 Mbit/s, just a tad lower than 25 Mbit/s of HDV. I've seen from numerous examples that Canon's implementation of MPEG-2 codec is very robust, and here is one more confirmation to it.
 
have u tried to log and transfer the footage again. i think your clip is corrupted. Just have to retransfer the file from the sd card to the computer and do a log and transfer again.
 
Rikki said:
Just shot a dance event that used a lot of strobe lights and this was the result :

badavchd.jpg


Here's a link to the footage : http://www.strathycruise.com/pics/badavchd.jpg.mp4

The screen grab is from the original MTS file, checked in both VLC player and Sony Vegas plus it looks just as bad when NeoScene converted as expected.

My Canon HV20 managed to handle this type of shooting perfectly with HDV so why does the pro grade AVCCAM not manage? :(
Click to expand...

The strobing and the fast panning stress out the codec, next time when you have strobe light, try not to pan so much and see if it help.
 
That's not a normal thing to happen. I've shot countless concerts with strobes and flashes and have never had anything like this as far as a breakdown. I'm shooting some on Tuesday and will post the footage.


What type of SD card are you using?
 
Ill upload some samples.

Its not a corrupt file so not point recopying the footage from the SD card :(

It happens when the camera is static and the strobe fires.

If the old HDV codec can handle it then surely the all singing all dancing AVCHD should do it?

Going out just now but will upload footage when I get back in thanks :)
 
towards the end.. there's some smoke and strobe footage.... and It holds up well.. I've never seen that kind of breakdown in the footie....


good luck
 
The main problem is you're using too low of a bitrate ~9Mb/s. I'm certain your HV20 footage would look just as bad or worse at that bitrate under the same shooting conditions

The other tips others have mentioned are also good (less motion, slower pans etc..). Use the highest bitrate setting in the future
 
Its set to PH mode which from what I have read is the best the camera offers.

The HV20 has no trouble with it, Ive shot in the same club with the same lighting system.
 
Perhaps there was some user error?

The sample you uploaded was ~9Mbps. It should be closer to ~21Mbps if shot in PH mode.

Perhaps you mistakenly used "HG" mode?

Perhaps your media is defective and bottlenecking the writes?
 
Last edited:
We've done a few sketches with strobe lights and such. I've never seen that sort of compression. Agree with PDR, you must have mistakenly used a lower quality.
 
I would do a quick test to make sure its not your camcorder or media issues.

Just shoot some sample footage right now in PH mode and check the bitrate.
 
PDR said:
I would do a quick test to make sure its not your camcorder or media issues.

Just shoot some sample footage right now in PH mode and check the bitrate.
Click to expand...

Not trying to jack this thread, but how does one check the bitrate of the files? I use FCP to log and transfer, but never noticed it displaying the bitrate. Thanks!
 
abeas said:
Not trying to jack this thread, but how does one check the bitrate of the files? I use FCP to log and transfer, but never noticed it displaying the bitrate. Thanks!
Click to expand...

On a mac, you could use mediainfo mac

On a pc, you could use mediainfo, avinaptic, or bitrate viewer

Mediainfo only reports header information and can be incorrect, but is usually "good enough". The proper way to do it is to use a low level stream analyser like elecard streameye
 
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