[gst-devel] How to control pipeline frame rate when my camera needs some time to get one frame data

[Zhao, Halley]

But the timestamp will be mess.
You could get some frames in a short time, then idle some time, then another some frames.


________________________________
From: thiagossantos at gmail.com [mailto:thiagossantos at gmail.com]
Sent: 2009年11月18日 7:19
To: Discussion of the development of GStreamer
Subject: Re: [gst-devel] How to control pipeline frame rate when my camera needs some time to get one frame data


On Tue, Nov 17, 2009 at 8:11 PM, Zhao, Halley <halley.zhao at intel.com<mailto:halley.zhao at intel.com>> wrote:
Hi all:
My camera needs ~20ms to get one frame of data, and a video sink in the pipeline needs ~4ms to render it.
But when I set pipeline fps to 35, I only got 20 fps (calculate by GST CLOCK). CPU is not busy at this time, only 60%.

I guess the reason is following:
When we got nth frame at time 0, gst framework schedule to get next frame after 30ms (1000/35), and when the camera src element got scheduled to create one frame, it needs 20ms to get the data.
Then the time between n frame and n+1 frame is 30+20=50ms, so I just got 20 fps.
Is my assumption right?
If yes, is there any way to adjust it?
You can speed it up by adding a queue right after your source element. It will create another thread to push data after it, the thread used to request a frame from the camera will quickly return to the source and it will request another one.


I had though to create another thread inside camera source, and prepare the frame data in a buffer before it is schedule.
However, I think it is hack, and make timestamp differ. I think it’s better settled inside gst framework.


ZHAO, Halley (Aihua)
Email: halley.zhao at intel.com
Tel: +86(21)61166476
iNet: 8821-6476
SSG/OTC/Moblin 3W038 Pole: F4


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