What is the use of preset bitrate exactly?

[reeldeal]

I started out using Ipowell's settings, which at first were great for a number of reasons. They got me going using the hack very quickly, and provided me a template from which to expand from. So I thank you for this (obviously can't thank Mr. GH13 enough).

Now I've started to test "C" settings which I'm finding to have even better quality (using Sandisk Extreme III Class 10 card).

So back to my question. What is preset bitrate exactly? Ipowell has used "180" for his settings. I've seen others use "500" and above. My thought was that if I was using "C" settings "440" would make sense since that is the max bitrate when using "C" settings.

Am I close to being right in this thinking process? What advantage does checking the preset bitrate box off have? What if I don't check this box off? Will it make things more stable or provide better quality?

Thanks for reading, I look forward to your responses.

 

[cbrandin]

I'm not sure anybody here knows exactly what it does. Understand, this is a reverse engineering effort so we can only make educated guesses.

One thing I know it does is affect how the codec starts up; that is, what the initial bitrate is when you press the one of the buttons that start the video capture. If it's set too high the camera will fail immediately if it starts in focus on a detailed scene. Too low and the first half-dozen frames, or so, might be a little soft. One way Lpowell achieved reliability was to set the preset bitrates to a low value.

My best advice is not to be too concerned with figuring out how high you can set them as there is little to be gained by doing so. Generally, I've found that raising them in proportion with the video bitrate results in camera failures. I just leave them at their defaults. That does, however, result in the first half-second of video possibly not being as sharp as the rest with highly detailed scenes.

An interesting note: In cases where video bitrate is set too high and the camera as a result frequently fails immediately if the scene is already in focus; when shooting starts out of focus the camera doesn't fail. Keeping the preset bitrates low has much the same effect as starting a clip out of focus as far as reliability is concerned.

Chris

 

[reeldeal]

Maakes more sense

Maakes more sense

Thanks for the response Chris. Right along the lines of what I was looking for. Just to recap, my tests have been with the kit 14-140 lens (OIS turned on, Smooth film mode -2,-1,0,0) and Sandisk Extreme III 8GB Class 10 card

Like many of you, I'm impressed with the "C" settings and I'm looking for more stability. Right now I have no issues recording FHD 24p @1/50 shutter speed (native 24p un-checked). Seems rock solid, and only recording TV static causes write errors.

I am having stability issues with SH mode @ 1/125 shutter speed. I have a good test area (epic foliage in my yard) and was consistently crashing almost immediately with the old settings of "500" for both Preset Bitrate 1 & 2.

After seeing your post, I changed Preset Bitrate1 to Lpowell's (thought the lower case l was an I- sorry bout that) setting of "180". I then set Preset Bitrate2 to "360" (just pulled that # out of thin air). As I was not interested in even higher quality, but rather stability, I decided to test the new settings out.

The camera no longer cause immediate write errors, and am able to record for a longer period using the same scene as before (lots of trees and grass, bright sunlight, swaying in the wind, etc.) It seems to crash when zooming in but seemed more stable when leaving the zoom alone.

My main focus for using this camera is concert footage, so in the next few weeks I will really be able to put this camera to the test. I'm more comfortable now using SH recording mode, just not sure of the results with bright lights and high intensity lasers, but we shall see.

 

[cbrandin]

With the C settings you can improve stability by going a little higher with the overall bitrate. I believe it suggests 52000000, which might be a little low. Try 54000000 instead. I use Transcend class 10 cards which fail every once in a while with the C settings in 720p mode, so I stick with the Lpowell settings which have been utterly reliable for me.

Chris

 

[MR Fanny]

remember with those high settings shooting below 1/50 in 720 will give you low Mb footage, 3Mb from my tests. I just stuck with the 32Mbit settings shooting at a dance event, with a fast enough lens and all the bright flashing lights to light faces up I found myself not needing to shoot at 1/30th at all. probably could have shot at Lpowells 40Mbit setting. Mbit rarely came close to 30Mbit because of the shallow DOF. I should do a quick scrub to see if the photog flashes and crazy lighting produced any mud but on first inspections I did not notice any. Might be a different story with the kit lens though.