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Video quality (bitrate) setting

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Offline leedsgreen

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Video quality (bitrate) setting
« on: 02 / December / 2009, 11:01:48 »
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Dear All,

I have a Canon A710is and now G9 and have managed to upload CHDK update on each. I have a question regarding video quality/bitrate settings. I notice that when CHDK is first loaded, the video quality/bitrate setting is at 84 and 1x, respectively. Does this mean that in its original form, each camera is not recording video at top quality but by chaging the settings to 100 and 3x, the video recording will be enhanced? If so, is there a noticeable improvement (or is it just for pixel-peepers)?! Of course, I can try this out for myself but just interested in any background info.

Thanks for any help,

Nick
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Offline fudgey

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Re: Video quality (bitrate) setting
« Reply #1 on: 02 / December / 2009, 12:36:24 »
Yes, you can probably increase video quality at least slightly by increasing bitrate. But increased file size is not the only caveat, SD card speed will eventually become more of an issue as you increase bitrate. You'll have to experiment to see what works for you reliably and how much perceived quality is altered.
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Offline Microfunguy

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Re: Video quality (bitrate) setting
« Reply #2 on: 02 / December / 2009, 13:07:59 »
Quote from: leedsgreen on 02 / December / 2009, 11:01:48
is it just for pixel-peepers)?

That was the conclusion of a respected, stereo movie-maker who did tests.

You have to pick a subject where there is a reasonable amount of activity and detail in the scene.

I have not done any tests, it would be interesting to see your results.


David
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Offline leedsgreen

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Re: Video quality (bitrate) setting
« Reply #3 on: 03 / December / 2009, 14:37:56 »
Sorry. Message removed. Can't get pics to load properly.
« Last Edit: 03 / December / 2009, 14:45:17 by leedsgreen »
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Offline Microfunguy

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Re: Video quality (bitrate) setting
« Reply #4 on: 03 / December / 2009, 14:41:29 »
Not sure you can use a static target.

After all, if nothing moves you only need to send one frame !


David
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Offline Microfunguy

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Re: Video quality (bitrate) setting
« Reply #5 on: 03 / December / 2009, 14:46:17 »
I  have loaded them as two layers in PSP and flip between them to compare.

There is no difference except the first one has more JPG artifacts when you converted it.


David
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Offline leedsgreen

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Re: Video quality (bitrate) setting
« Reply #6 on: 03 / December / 2009, 14:49:41 »
David,

That was a quick reply! My reason for test is to use camera on my telescope for hi-res images of moon. My sense is that the video mode works at a much higher ISO so I can push the magnification up and then stack to reduce noise. When I get the next clear night, I will include results.

Glad those two did load up. Yeah, the artefacts seemed less present in 3x one, so will use that in future. Although, may have to get faster SD card, as mine appeared to struggle somewhat.

Nick
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Offline Microfunguy

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Re: Video quality (bitrate) setting
« Reply #7 on: 03 / December / 2009, 16:47:19 »
I have just realised a couple of thongs...

Both your cameras use MJPEG encoding (every frame a JPG), so the images you posted really were frames extracted from the movie and the artefacts exist in the original movie, not because of anything you did later.

Secondly, your post says 'Video quality (bitrate) setting' whereas you are only using bitrate.

As the amount of detail in the scene increases (when the moon is nice and sharp for a fraction of a second) so too will the amount of JPG compression.

You really need to set a certain acceptable quality (that does not show JPG artefacts).
Then, as the detail in the scene increases the bitrate will increase so that the amount of JPG compression remains the same.

Above a certain quality setting little will be gained and if too high your camera will crash.

You need a fast, low-level formatted card anyway.


David
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