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| llm | this example https://linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/capture.c.html works with my usb webcam out of the box, if disconnect the usb cam while running (i get an VIDIOC_DQBUF, error: ENODEV error), after restarting the example i always get an timeout in select, the only "solution" i found is to open/close the webcam with the VLC player aft
er that the example works as expected - this behavior is reproducible, any idea what is wrong with the example or what is VLC player doing to "fix" the timeout in select | [08:58] |
| hverkuil | llm: when you disconnect the webcam the video device you've opened is no longer connected to any hardware and in fact is removed from /dev. When you plug it back in a new video device appears, and you have to open that. | [09:09] |
| llm | my webcam gets always connected as /dev/video0, its hard coded in the sample and in VLC i also select /dev/vide0, the sample would fail on open if the device would not be available - or?
this is what i do, start capture sample, let it run, disconnect webcam (/dev/video0 gets removed), capture sample fails with ENODEV and exit, connect webcam (/dev/video0 appears), start capture sample, device gets opened, but select fails with timeout and exits at this point i can start sample capture serveral times and will always exit with select timeout, stable but if i open/close the webcam with the VLC player everything went back to normal with capture sample | [09:19] |
| hverkuil | is it a uvc webcam? | [09:23] |
| llm | i do not run the sample or VLC together
Its a 8 years old Microsoft LifeCam, "uvcvideo: Found UVC 1.00 device Microsoft® LifeCam Cinema(TM) (045e:075d)" works without any problem in serval linux apps in apps that i developed myself and others like vlc, gstreamer, ... Ubuntu 18.04, 4.18.0-23-generic i first thought it was an implementation problem on my side, but it also does not work with the v4l2 given capture sample | [09:24] |
| hverkuil | I'll have to test that example program.
what options do you use with the capture app? | [09:32] |
| llm | default, just start the sample, will connect to video0 and take 70 frames, in between i disconnect, wait for fail/exit and retry after connecting the cam again
you can change the device with -d | [09:34] |
| hverkuil | Hmm, the select timeout is just 2 seconds in that example. It looks like it can time a uvc webcam longer to start streaming. | [09:38] |
| llm | but without doing the disconnect 2sec are never a problem
and after "cleanup" with vlc the 2sec are no problem and even 20sec are not enough | [09:43] |
| hverkuil | lunch, back later | [09:45] |
| llm | also taking a shot with "gst-launch-1.0 v4l2src num-buffers=1" will fix the timeout problem for the capture sample | [09:55] |
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| hverkuil | llm: I can't reproduce the problem after increasing the select timeout to 20 seconds.
sorry | [10:53] |
| llm | but the VLC player and gstreamer don't take 20 seconds rather <1sec
What camera are you using? even a 60sec timeout does not work, could there be a bug in the lifecam driver? btw: brand new Dell Laptop + Fresh Ubuntu 18.04 installation | [10:55] |
| hverkuil | also a uvc camera. All uvc webcams use the same driver. | [11:00] |
| llm | i get call trace logs on disconnect while running the sample capture: https://pastebin.com/jrx3QpxW
could it be that only the Microsoft Lifecam got this problem? any idea why using gstreamer or VLC on the device fixes the problem for the capture sample | [11:02] |
| hverkuil | BTW, vlc also takes a long time after the webcam is first plugged in before it starts. In general, the first time I start capturing, regardless of the application, it takes several seconds.
Are you sure when you increased the timeout in the example application that you recompiled it and were actually using the recompiled app? | [11:04] |
| llm | yes select waits for 60 second before timeout
yes select waits for 60 second before timeout deleted the excutable and recompiled even 100sec won't work and its the same source as in the v4l example | [11:13] |
| hverkuil | llm: sorry, I can't reproduce it. And I have other things to do as well. Perhaps it is the webcam somehow. | [11:19] |
| llm | Ok, thanks - will try another webcam tomorrow | [11:20] |
| but still benchmarking VLC and gstreamer show that the initalization time is < 1sec | [11:25] | |
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| svarbanov | hverkuil, what is the idea behind these checks : https://git.linuxtv.org/v4l-utils.git/tree/utils/v4l2-compliance/v4l2-test-buffers.cpp#n1390 | [13:51] |
| hverkuil | Testing corner cases. | [14:00] |
| svarbanov | hverkuil, :) good answer | [14:03] |
| llm | another strange result: i start the capture sample which runs without any error, collecting 70 frames - but the usb cable was disconnected?, second try get me to an open(...) error ... very strange | [14:05] |
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| and the v4l2 sample exits on every error?? | [14:38] | |
| hverkuil | llm: can you run v4l2-ctl -D -d /dev/video0? Are you sure you are testing with the video device for the webcam?
You're seeing very strange things. | [14:44] |
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| llm | https://pastebin.com/Ka6wdHNd
im sure | [15:04] |
| hverkuil | weird
if the usb cable is disconnected then the video device disappears as well, so how on earth can you run the capture app and have it stream? | [15:06] |
| llm | vlc and gstreamer are 100% working in all cases, only the v4l capture sample got this behavior | [15:07] |
| hverkuil | Is your capture code the same as this: https://git.linuxtv.org/v4l-utils.git/plain/contrib/test/capture-example.c | [15:08] |
| llm | i have no idea - no errors from ioctrl or any other call, after the run i saw the disconnected cable on my desk...
yes it is this example, 100% identical using diff Is there an official test for usb disconnect scenarios? | [15:08] |
| hverkuil | llm: no idea, I'm not the usb expert.
I'm certain it's tested, but whether there is an 'official' test is something else. The problem is that the test app doesn't do anything strange. It's standard code. Only the select timeout is on the low side. And I can't reproduce this issue at all. which kernel version are you running? | [15:14] |
| llm | freshly installed Ubuntu 18.04, 4.18.0-23-generic, on 5 month old professional grade Dell Laptop | [15:22] |
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| ezequielg | hverkuil: hi \o let me know if/when you have some time to discuss the VP8 uAPI and struct layout/alignment requirements for uAPIs. | [15:38] |
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| hverkuil | ezequielg: tomorrow? | [15:58] |
| ezequielg | works for me.
bbrezillon: ^ | [15:58] |
| hverkuil | It's 18:00 here, what time is it for you? 13:00? | [15:59] |
| ezequielg | yes.
i can be here, as early as 8am. | [16:01] |
| hverkuil | ezequielg: would 15:00 my time, 10:00 your time work? | [16:02] |
| ezequielg | it's perfect :-) | [16:02] |
| hverkuil | excellent. | [16:03] |
| llm | i will check my logitech and a different web cam tomorrow on 3 different hardware platforms maybe the systems behave different
time for biobreak | [16:15] |
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