[Elphel-support] how to increase the frame rate?

[Andrey Filippov]

On Tue, Nov 16, 2010 at 7:37 PM, Ákos Maróy <akos at maroy.hu> wrote:

> Hi,
>
> I wonder how to increase the framerate on an elphel camera?
>
> When I do full resolution, mplayer seems to report a framerate of 10fps
> or less:
>
> VIDEO:  [MJPG]  0x0  0bpp  7.000 fps    0.0 kbps ( 0.0 kbyte/s)
>
>
> but interestingly, I get the same framerate if I use half or quarter of
> the image dimensions. also, even at full resolution, the CPU load on the
> camera is actually not really high:
>


Akos,

the most likely reason (proved by the steady fps regardless of the frame
size) is the exposure time. Obviously the frame rate can not be higher than
1/exposure time, so please check that - in the camera GUI the frame rate
(the rate sensor currently operates at) is shown in different colors,
depending on the source of the limitation.  You may slightly decrease the
required exposure time by increasing analog gain(s)

Potentially there can be several bottlenecks in the camera:

1 - exposure time
2 - sensor limitations - for each frame dimensions, decimation and binning
and operation mode (free running/ triggered) there is a certain minimal
frame period.
3 - camera FPGA - in JPEG mode it can compress 53MPix/sec (average, peak can
go higher), in JP4 mode - 80MPix/sec. Sensor gets up to ~75MPix sec
(average) at the full frame, lower at smaller ones. So in JPEG mode only
with the largest frames it can be an issue, in JP4 - never.
4 - bandwidth of the network - up to full 10 megabytes/second over 100mbps
network, when you hit that limit you can try lowering the compression
quality with the same frame size/rate.
5 - similarly - HDD bandwidth, it is approximately 16MB/sec, limited by the
ETRAX FS CPU, improving results when lowering compression quality can be an
indicator. Additionally if the HDD has large directory with files (best
performance is achieved with simple *.mov files and large limits on the file
segment) there could be frame drops when opening a new file segment - the
camera videobuffer fro the compressed frames is 19MB, so you can calculate
the time that the file system has to close/open file.

Andrey
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