Andrew Lunn wrote:
Brendan Hoar wrote:
On Tue, 20 Sep 2005, Chris Kennedy wrote:
Rolf Kistler wrote:
Hi all,
We have used ivtv and two PVR-350 to successfully to stream mpeg-2
Video/Audio data over the network using on one side the analog composite
input (camera) and on the other side the analog composite output (TV
screen). As long as one wants to transport surveillance data or a movie,
this solution just works fine.
Now the problem is that if the task is to control a camera or talk to
someone on the other end, the 2-3 seconds delay in our system is too much.
This is from it being compressed video, encoding always will introduce a
delay, in every encoding system out there.
I would expect the delay to be determined my the pattern of I, B and P
frames. I guess the minimum delay is that of between two I frames.
What patterns of I, P and B does the PVR-350 use? How often does it
repeat? Say it repeats after 10 frames. That 10/25 of a second, where
as the original poster was talking about 2 to 3 seconds.
Is there any way to change the pattern of I, B and P frames?
It uses pretty much the standard MPEG2 spec for Standard Definition
video, 15 frames per Group of Pictures, consisting of....
7489690: 0x00: Picture (I-Frame) Start (2)
7544860: 0x00: Picture (B-Frame) Start (0)
7563292: 0x00: Picture (B-Frame) Start (1)
7581732: 0x00: Picture (P-Frame) Start (5)
7612444: 0x00: Picture (B-Frame) Start (3)
7630876: 0x00: Picture (B-Frame) Start (4)
7649316: 0x00: Picture (P-Frame) Start (8)
7677980: 0x00: Picture (B-Frame) Start (6)
7696412: 0x00: Picture (B-Frame) Start (7)
7714852: 0x00: Picture (P-Frame) Start (11)
7743516: 0x00: Picture (B-Frame) Start (9)
7761948: 0x00: Picture (B-Frame) Start (10)
7780388: 0x00: Picture (P-Frame) Start (14)
7811100: 0x00: Picture (B-Frame) Start (12)
7829532: 0x00: Picture (B-Frame) Start (13)
This is really not something the encoding chip was designed to handle
much else besides a 6/12/15/30 frame GOP (and 30 frames will corrupt at
scene changes sometimes). I think 6 frame GOP testing should prove or
disprove your theory, since should be half as long of a delay using that
setting.
Just run this `ivtvctl -c framespergop=6` command to setup 6
framespergop (when not encoding yet of course :-).
Thanks,
Chris
Andrew
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Chris Kennedy
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