Low FPS when accesing iPhone video output image buffer

2 down vote favorite
Hi, I'm trying to do some image processing on iPhone. I'm using http://developer.apple.com/library/ios/#qa/qa2010/qa1702.html to capture the camera frames.
My problem is that when I'm trying to access the captured buffer, the camera FPS drops from 30 to about 20. Does anybody knows how I can fix it?
I use the lowest capture quality I could find (AVCaptureSessionPresetLow = 192x144) in kCVPixelFormatType_32BGRA format. If anybody knows a lower quality I could use, I'm willing to try it.
When I do the same image access on other platforms, like Symbian, it works OK.

I also happen to have T-Mobile, but the problem happened on WiFi as well as you mentioned and therefore didn't seem to be related to carrier.
I expect your videos are playing normally again like mine since yesterday morning. I guess it had something to do with the video codecs/standards being used by major video service providers like you thought, but I found it curious that so many different video sources beyond YouTube caused me the same problem during that time. I did find that Daily Motion worked fine when the other services weren't working, so I knew it had to be service (and what standards they were using) specific.
Still, how were there not tons and tons of other people experiencing this!? I had it happen on both my 6+ and my iPhone 4. Maybe there were other factors specific to my area/connection (outside of connection speed which was always fine) that resulted in it, but still...

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I have the same config as you: I have been using it for years to view on my tv dvds or videos from the web.
To my knowledge there is no way to acheive what you wish: when you plug the adaptor in the mac adjust to your output source and its main display (the g5 display) will reflect that with the result that it becomes very difficult to use.
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Hello. When i am running ffmpeg on 1280x768 resolution, program record with ~100fps, When i change resolution to my native(1366x768), program record with ~29 fps and system running slow.
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frame= 66 fps=0.0 q=17.0 size= 417kB time=00:00:00.30 bitrate=11374.4kbitsframe= 132 fps=131 q=17.0 size= 449kB time=00:00:00.63 bitrate=5832.5kbits/frame= 199 fps=132 q=17.0 size= 449kB time=00:00:00.96 bitrate=3807.7kbits/frame= 256 fps=127 q=24.0 size= 481kB time=00:00:01.25 bitrate=3149.3kbits/frame= 321 fps=128 q=17.0 size= 769kB time=00:00:01.57 bitrate=4000.0kbits/
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Linux adrian 3.8.3-2-ARCH #1 SMP PREEMPT Sun Mar 17 13:04:22 CET 2013 x86_64 GNU/Linux
hardware info:
i5 8gb ram 630m
Do u know how to get better fps on my native resolution?
THX
Dziękuje i Pozdrawiam:}
Last edited by Vatri91 (2013-03-23 11:30:29)

Couple of thoughts.
30 fps is DVD quality. I would drop (-r 100) to (-r 24) I don't know what you are gaining capturing at 100fps.
You can also dump to raw video then encode the file later.
You can lower the video bitrate that you encode to (c:v libx264 -b:v 500k). Depends on how active your screen is. If you are just doing a tutorial of something then you may be able to drop down to (300k). Anything under (1000k) will be noticeable if you have a lot of movement on the screen.
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If framerate is dropping below specified while capturing with ffmpeg then, you'll have to lower the bitrate that you are encoding at, dump the stream as a raw video then encode it later, capture a smaller area of screen, or I hear that recordmydesktop does well.
EDIT: reason for edit, syntax correction.
Last edited by teckk (2013-03-27 14:57:33)

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Low FPS when accesing iPhone video output image buffer

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