Re: Python and webcam capture delay?
On Tue, 07 Jul 2009 22:11:12 -0700, Tim Roberts wrote: >>The webcam is bound to do some encoding; most of them use USB "full speed" >>(12Mbit/sec), which isn't enough for raw 640x480x24...@30fps data. > > That's not true. Most of the web cams made in the last 5 years or so run > at high speed, 480 Mbps. Full speed only gets you 1 fps at 640x480 > uncompressed, so it's really only useful for the most primitive video > conference cams. The very earliest models typically only did 320x200, while later USB-1 webcams used onboard compression to get a decent framerate. For internet use, 12Mbps isn't that much of an obstacle; the internet connection's upload speed is more likely to be the limiting factor. Faster speeds are more useful for things like LAN-based CCTV systems. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
On Tue, 07 Jul 2009 22:49:22 -0700, Dennis Lee Bieber wrote: > On Tue, 07 Jul 2009 23:37:43 +0100, Nobody > declaimed the following in gmane.comp.python.general: > >> AFAIK, the only real difference between "USB-1 conformant" and "USB-2 >> conformant" is that the latter actually passed a test of its ability to >> say "no, I can't do high-speed", while the former didn't. The check for >> high-speed capability was designed such that it shouldn't cause problems >> for USB-1 devices, but individual USB-1 devices weren't actually tested >> for this. > > USB-1 or USB-1.1? As I recall the latter is capable of 11Mbps > whereas the original USB spec was much lower... (of course, USB 2 at top > is 480Mbps) USB 1.0 supports 1.5Mbps (low-speed) and 12MBps (full-speed). Hosts and hubs must support both, functions (devices) can use either. USB 1.1 was a bug-fix release which solved some interoperability issues arising from ambiguities in the USB 1.0 standard. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
Nobody wrote: > >The webcam is bound to do some encoding; most of them use USB "full speed" >(12Mbit/sec), which isn't enough for raw 640x480x24...@30fps data. That's not true. Most of the web cams made in the last 5 years or so run at high speed, 480 Mbps. Full speed only gets you 1 fps at 640x480 uncompressed, so it's really only useful for the most primitive video conference cams. -- Tim Roberts, t...@probo.com Providenza & Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
On Tue, 07 Jul 2009 09:01:39 +0300, jack catcher (nick) wrote: > Thanks for the comments. Unfortunately, such specifications aren't easy > to find, even in reviews. Fortunately several newer webcams seem at > least to use usb2. Supporting USB-2 doesn't mean that the camera necessarily uses high-speed (480Mbit/sec). AFAIK, the only real difference between "USB-1 conformant" and "USB-2 conformant" is that the latter actually passed a test of its ability to say "no, I can't do high-speed", while the former didn't. The check for high-speed capability was designed such that it shouldn't cause problems for USB-1 devices, but individual USB-1 devices weren't actually tested for this. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
Nobody kirjoitti: On Mon, 06 Jul 2009 20:41:03 +0300, jack catcher (nick) wrote: Does the webcam just deliver frames, or are you getting frames out of a decoder layer? If it's the latter, you want to distribute the encoded video, which should be much lower bandwidth. Exactly how you do that depends a bit on what format the webcam claims to deliver. Well, getting already encoded video from the webcam sounds almost like a free lunch (which it probably is not). At least I wouldn't want to get too long a delay because of the encoding. I haven't got the webcam(s) yet, and I guess I can basically purchase any ones I find suitable for getting the job done. Any recommendations? The webcam is bound to do some encoding; most of them use USB "full speed" (12Mbit/sec), which isn't enough for raw 640x480x24...@30fps data. Chroma subsampling and JPEG compression will both reduce the bandwidth without introducing noticable latency (the compression time will be no more than one frame). Temporal compression will reduce the bandwidth further. Using B-frames (frames which contain the differences from a predicted frame which is based upon both previous and subsequent frames) will provide more compression, but increases the latency significantly. For this reason, the compression built into video cameras normally only uses P-frames (frames which contain the differences from a predicted frame which is based only upon previous frames). The biggest issue is likely to be finding latency specifications, followed by finding a camera which meets your latency requirement. Thanks for the comments. Unfortunately, such specifications aren't easy to find, even in reviews. Fortunately several newer webcams seem at least to use usb2. Regarding Python, I'll have to check whether the ImageCapture extension works at all, as someone suggested earlier, and the possibility of using DirectShow. I'm still considering Matlab as an option for Python here. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
On Mon, 06 Jul 2009 18:41:03 +0100, jack catcher (nick) wrote: Rhodri James kirjoitti: Does the webcam just deliver frames, or are you getting frames out of a decoder layer? If it's the latter, you want to distribute the encoded video, which should be much lower bandwidth. Exactly how you do that depends a bit on what format the webcam claims to deliver. Well, getting already encoded video from the webcam sounds almost like a free lunch (which it probably is not). At least I wouldn't want to get too long a delay because of the encoding. Not so unlikely as you might think, since there are very basic M-JPEG and MPEG-2 on-chip encoders available, and the webcam will have to do some compression to get the video data into the computer. USB is not as fast as it would like to pretend. I haven't got the webcam(s) yet, and I guess I can basically purchase any ones I find suitable for getting the job done. Any recommendations? Sorry, no. I'm used to getting my video feeds down fibre-optic cables :-) -- Rhodri James *-* Wildebeest Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
On Mon, 06 Jul 2009 20:41:03 +0300, jack catcher (nick) wrote: >> Does the webcam just deliver frames, or are you getting frames out of >> a decoder layer? If it's the latter, you want to distribute the encoded >> video, which should be much lower bandwidth. Exactly how you do that >> depends a bit on what format the webcam claims to deliver. > > Well, getting already encoded video from the webcam sounds almost like a > free lunch (which it probably is not). At least I wouldn't want to get > too long a delay because of the encoding. > > I haven't got the webcam(s) yet, and I guess I can basically purchase > any ones I find suitable for getting the job done. Any recommendations? The webcam is bound to do some encoding; most of them use USB "full speed" (12Mbit/sec), which isn't enough for raw 640x480x24...@30fps data. Chroma subsampling and JPEG compression will both reduce the bandwidth without introducing noticable latency (the compression time will be no more than one frame). Temporal compression will reduce the bandwidth further. Using B-frames (frames which contain the differences from a predicted frame which is based upon both previous and subsequent frames) will provide more compression, but increases the latency significantly. For this reason, the compression built into video cameras normally only uses P-frames (frames which contain the differences from a predicted frame which is based only upon previous frames). The biggest issue is likely to be finding latency specifications, followed by finding a camera which meets your latency requirement. Also, any "read frame, write frame" loops will add an additional frame of latency, as you can't start writing the first byte of the frame until after you've read the last byte of the frame. Video APIs which let you get rows as they're decoded are rare. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
Rhodri James kirjoitti: On Mon, 06 Jul 2009 07:10:38 +0100, jack catcher (nick) wrote: Tim Roberts kirjoitti: "jack catcher (nick)" wrote: I'm thinking of using Python for capturing and showing live webcam stream simultaneously between two computers via local area network. Operating system is Windows. I'm going to begin with VideoCapture extension, no ideas about other implementation yet. Do you have any suggestions on how short delay I should hope to achieve in showing the video? This would be part of a psychological experiment, so I would need to deliver the video stream with a reasonable delay (say, below 100ms). You need to do the math on this. Remember that a full 640x480 RGB stream at 30 frames per second runs 28 megabytes per second. That's more than twice what a 100 megabit network can pump. You can probably use Python to oversee this, but you might want to consider using lower-level code to control the actual hardware. If you are targeting Windows, for example, you could write a DirectShow graph to pump into a renderer that transmits out to a network, then another graph to receive from the network and display it. You can manage the network latency by adding a delays in the local graph. Thanks Tim, you're correct about the math. What is your main point about DirectShow: that it is generally faster and more reliable than doing the job high-level, or that one could use coding/decoding in DirectShow to speed up the transmission? I think the latter would be a great idea if the latency were tolerable. On the other hand, I'd like to keep things simple and do all the programming in Python. I've got no experience with DirectShow, but I guess the filters need to be programmed in C++ and called from Python? Another option might be to use resolution 320x...@15fps. Does the webcam just deliver frames, or are you getting frames out of a decoder layer? If it's the latter, you want to distribute the encoded video, which should be much lower bandwidth. Exactly how you do that depends a bit on what format the webcam claims to deliver. Well, getting already encoded video from the webcam sounds almost like a free lunch (which it probably is not). At least I wouldn't want to get too long a delay because of the encoding. I haven't got the webcam(s) yet, and I guess I can basically purchase any ones I find suitable for getting the job done. Any recommendations? -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
On Mon, 06 Jul 2009 07:10:38 +0100, jack catcher (nick) wrote: Tim Roberts kirjoitti: "jack catcher (nick)" wrote: I'm thinking of using Python for capturing and showing live webcam stream simultaneously between two computers via local area network. Operating system is Windows. I'm going to begin with VideoCapture extension, no ideas about other implementation yet. Do you have any suggestions on how short delay I should hope to achieve in showing the video? This would be part of a psychological experiment, so I would need to deliver the video stream with a reasonable delay (say, below 100ms). You need to do the math on this. Remember that a full 640x480 RGB stream at 30 frames per second runs 28 megabytes per second. That's more than twice what a 100 megabit network can pump. You can probably use Python to oversee this, but you might want to consider using lower-level code to control the actual hardware. If you are targeting Windows, for example, you could write a DirectShow graph to pump into a renderer that transmits out to a network, then another graph to receive from the network and display it. You can manage the network latency by adding a delays in the local graph. Thanks Tim, you're correct about the math. What is your main point about DirectShow: that it is generally faster and more reliable than doing the job high-level, or that one could use coding/decoding in DirectShow to speed up the transmission? I think the latter would be a great idea if the latency were tolerable. On the other hand, I'd like to keep things simple and do all the programming in Python. I've got no experience with DirectShow, but I guess the filters need to be programmed in C++ and called from Python? Another option might be to use resolution 320x...@15fps. Does the webcam just deliver frames, or are you getting frames out of a decoder layer? If it's the latter, you want to distribute the encoded video, which should be much lower bandwidth. Exactly how you do that depends a bit on what format the webcam claims to deliver. -- Rhodri James *-* Wildebeest Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
jack catcher (nick) wrote: Hi, I'm thinking of using Python for capturing and showing live webcam stream simultaneously between two computers via local area network. Operating system is Windows. I'm going to begin with VideoCapture extension, no ideas about other implementation yet. Do you have any suggestions on how short delay I should hope to achieve in showing the video? This would be part of a psychological experiment, so I would need to deliver the video stream with a reasonable delay (say, below 100ms). I would first check if video capture extension works anyway. I couldn't get it working, ... ... it seems to start ok ... but moving the captured window, ... or sometimes even just moving the mouse hangs the program :-( So I'm still looking for a good / open source workiing video capture in Python. I can make a good working capture in delphi, make a DLL or ActiveX from that and use it in Python, but I'm not allowed to ditribute these. cheers, Stef -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
Tim Roberts kirjoitti: "jack catcher (nick)" wrote: I'm thinking of using Python for capturing and showing live webcam stream simultaneously between two computers via local area network. Operating system is Windows. I'm going to begin with VideoCapture extension, no ideas about other implementation yet. Do you have any suggestions on how short delay I should hope to achieve in showing the video? This would be part of a psychological experiment, so I would need to deliver the video stream with a reasonable delay (say, below 100ms). You need to do the math on this. Remember that a full 640x480 RGB stream at 30 frames per second runs 28 megabytes per second. That's more than twice what a 100 megabit network can pump. You can probably use Python to oversee this, but you might want to consider using lower-level code to control the actual hardware. If you are targeting Windows, for example, you could write a DirectShow graph to pump into a renderer that transmits out to a network, then another graph to receive from the network and display it. You can manage the network latency by adding a delays in the local graph. Thanks Tim, you're correct about the math. What is your main point about DirectShow: that it is generally faster and more reliable than doing the job high-level, or that one could use coding/decoding in DirectShow to speed up the transmission? I think the latter would be a great idea if the latency were tolerable. On the other hand, I'd like to keep things simple and do all the programming in Python. I've got no experience with DirectShow, but I guess the filters need to be programmed in C++ and called from Python? Another option might be to use resolution 320x...@15fps. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python and webcam capture delay?
"jack catcher (nick)" wrote: > >I'm thinking of using Python for capturing and showing live webcam >stream simultaneously between two computers via local area network. >Operating system is Windows. I'm going to begin with VideoCapture >extension, no ideas about other implementation yet. Do you have any >suggestions on how short delay I should hope to achieve in showing the >video? This would be part of a psychological experiment, so I would need >to deliver the video stream with a reasonable delay (say, below 100ms). You need to do the math on this. Remember that a full 640x480 RGB stream at 30 frames per second runs 28 megabytes per second. That's more than twice what a 100 megabit network can pump. You can probably use Python to oversee this, but you might want to consider using lower-level code to control the actual hardware. If you are targeting Windows, for example, you could write a DirectShow graph to pump into a renderer that transmits out to a network, then another graph to receive from the network and display it. You can manage the network latency by adding a delays in the local graph. -- Tim Roberts, t...@probo.com Providenza & Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Python and webcam capture delay?
Hi, I'm thinking of using Python for capturing and showing live webcam stream simultaneously between two computers via local area network. Operating system is Windows. I'm going to begin with VideoCapture extension, no ideas about other implementation yet. Do you have any suggestions on how short delay I should hope to achieve in showing the video? This would be part of a psychological experiment, so I would need to deliver the video stream with a reasonable delay (say, below 100ms). -- http://mail.python.org/mailman/listinfo/python-list
Re: python and webcam
Hi again,
I've tried a the Sane interface from PIL and I get the following
error, when I run the demo_pil.py from the Sane directory.
SANE version: (16777231, 1, 0, 15)
Available devices= [('v4l:/dev/video0', 'Noname', 'Logitech QuickCam
Pro 3000', 'virtual device')]
Traceback (most recent call last):
File "/PyWebcam/demo_pil.py", line 17, in ?
s.br_x=320. ; s.br_y=240.
File "/usr/lib/python2.4/site-packages/sane.py", line 150, in
__setattr__
raise AttributeError, 'Inactive option: '+key
AttributeError: Inactive option: br_x
Next, I looked at v4l support for python with absolutely no
documentation. I tried to build the modules and I get the following
error:
python setup.py build
running build
running build_ext
building 'v4l' extension
gcc -pthread -fno-strict-aliasing -DNDEBUG -O2 -g -pipe
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -m32 -march=i386 -mtune=pentium4
-fasynchronous-unwind-tables -D_GN U_SOURCE -fPIC -fPIC
-I/usr/include/python2.4 -c v4l.c -o build/temp.linux-i686- 2.4/v4l.o
v4l.c: In function 'v4l_getImage':
v4l.c:890: warning: pointer targets in assignment differ in signedness
v4l.c: In function 'initv4l':
v4l.c:1585: error: 'VIDEO_AUDIO_BALANCE' undeclared (first use in
this function)
v4l.c:1585: error: (Each undeclared identifier is reported only once
v4l.c:1585: error: for each function it appears in.)
error: command 'gcc' failed with exit status 1
I also looked at libfg http://antonym.org/libfg and I get the following
errors again:
---
python setup.py build
running build
running build_ext
building 'fg' extension
gcc -pthread -shared build/temp.linux-i686-2.4/fgmodule.o -L. -lfg -o
build/lib.linux-i686-2.4/fg.so
/usr/bin/ld: cannot find -lfg
collect2: ld returned 1 exit status
error: command 'gcc' failed with exit status 1
I google-ed extensively have so far found only these three packages.
Any ideas why I get these error messages?
--
http://mail.python.org/mailman/listinfo/python-list
Re: python and webcam
"dfaber" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > Hi, > I have Logitech webcam and I need to grab images on Fedora Core 4 (not > my favorite distro). Are there any python modules available for doing > this? Any hints or suggestions would be welcome. If is one of their ball cameras (or other shape)b with a USB connection, then I would expect that you access it through the TWAIN protocol. (I don't know how to do that from python, but wish I did!). If it is a truly web-ready camera with a built-in server and ethernet connection, then you access it via an http request to its inet address. -- http://mail.python.org/mailman/listinfo/python-list
Re: python and webcam
Thank you for your help. I will look around for v4l modules too. -- http://mail.python.org/mailman/listinfo/python-list
Re: python and webcam
"dfaber" <[EMAIL PROTECTED]> wrote: > It is a Win32 Python Extension. I am looking for something that work > on Linux. here's one: http://antonym.org/libfg (for more alternatives, google for "python webcam linux" or some variation thereof) -- http://mail.python.org/mailman/listinfo/python-list
Re: python and webcam
It is a Win32 Python Extension. I am looking for something that work on Linux. -- http://mail.python.org/mailman/listinfo/python-list
Re: python and webcam
In article <[EMAIL PROTECTED]>, dfaber wrote: > I have Logitech webcam and I need to grab images on Fedora Core 4 (not >my favorite distro). Are there any python modules available for doing >this? Any hints or suggestions would be welcome. You can try this : http://videocapture.sourceforge.net/ -- http://mail.python.org/mailman/listinfo/python-list
python and webcam
Hi, I have Logitech webcam and I need to grab images on Fedora Core 4 (not my favorite distro). Are there any python modules available for doing this? Any hints or suggestions would be welcome. Thanks. -- http://mail.python.org/mailman/listinfo/python-list
