frames out of sequence when back-stepping thru recordings

pozzello

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I tried to search for this issue here, but either the new UI has a lame search engine or I'm getting old (maybe both).

I've always been annoyed by how frames seem to jump around when stepping back thru
recorded video frame-by-frame (in the console or the stock web UI and even UI2.htm)
Currently on BI 4.5.2.7, but have noticed this since way back in the early 4.x days...

It's as if the math used to calculate the frame offset from the i-frame
is somehow out of whack when stepping backwards. I record to BVR format (direct to disk),
and it happens with all my cams (Hikvisions and Huisin mini-ptz's,
all set to 10FPS & i-frame every 10 frames, ie, 1 per second)

I've made a recording of this effect which i hope illustrates the issue:
Blue Iris 5_15_2017 6_13_09 PM
i first play thru the clip, then hit the step-back button repeatedly until the car is out of frame again,
then step forward, then back again.

Is this a known issue? Has anyone else around here noticed/reported it?
It's not that big a deal, cuz I can always find the frame i need by stepping thru it forward,
but it sure would be nice to have reverse step-back work just as well...

I've emailed BI support, but am not on a plan, so who knows if/when Ken will read it or do anything about this.

Thanx, Paul.
 

Jareds

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Never noticed before. If it were a problem I would think I would have seen it with my own eyes. I see what ur saying tho, just never had this happen to my knowledge and I just looked at a couple clips. What FPS are u using what iframe interval?
 

SyconsciousAu

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That's random and I've never seen it happen before. The frames in the file must be in the right order, or it would do the same thing forwards. Do all files do it, or just the odd one here and there?
 

pozzello

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Well, if you think about how the files are encoded, there's a 'full frame' (or i-frame) every second (as my cams are configured),
and the other frames in between are represented as diffs or deltas (changes) from the previous
(and sometimes next full frame, if using b-frames, but i dunno if that's involved here).

So to see one of the frames in between i-frames, BI has to calculate the offset from the previous i-frame, and the behavior I see
when stepping backwards seems to indicate it's just doing bad math there, for me at least.

As i mentioned in my original post, I see it with all my cams, all set to 10FPS and using 1 i-frame per second ('interval' set to 10 in Hik UI).
For me, this happens with ALL recordings (from Hikvision 2032's, 2332's, 2335's & 2355's, Huisun Mini PTZ's, and even a couple of LongSe S500's).
It happens when stepping backwards (playing in reverse as slow as possible) in the BI console, the BI standard web interface, AND even
in bp2008's UI2.html.

I'm recording BVR direct to disk, but also using hardware encoding/decoding. Will play with those settings and see if it has any effect,
but i'm kinda surprised this isn't something that others have experienced as well. I just figured it's an issue we'd all just accepted
as part of the package...

another example, using a different camera and UI2.htm as the interface: out
watch the white car jump back & forth as i back up thru the clip...
 
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SyconsciousAu

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Ok I've just seen this issue but under different circumstances. I've been playing with openalpr and have written a batch script which pulls images from the camera using the BI interface at 100ms intervals. Now in theory this should give me 10 frames labelled image.jpg to image_9.jpg that are sequential and in order. I'm getting my 10 frames but they are being recorded out of order and the cars are doing the step back we see in your clips. Again no idea why.
 

pozzello

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and i heard from Ken. he says

<quote>
Please check to see how you are encoding your video. The effect that you describe may occur if the decoder sets up a "pipe line" where the decoded video is not immediately available until one or more additional frames are decoded, giving you a "Delay" in the output.
If you set the number of b-frames to 0, or the encoding to "base line" this will help.
</quote>

which sounds reasonable, except that my cams don't have any options for b-frames specifically or even the encoding proflie.
'video' tab has a picklist for profile, but the only option is 'main', no 'baseline' available... Hikvison 2032's, 2232's, 2235's etc.
nothing exotic here...

I'm gonna play around with hardware encoding/decoding settings and see if it makes a diff, but as i remember,
i've had this problem since before HW support was even available, so i'm really feeling this is a BI-specific issue, aka bug...
 

pozzello

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OK, some trial and error futzing around and I think I found my culprit.

for me, it's the "also use for BVR playback" option of the hardware decoding settings in the BI video tab for each cam.
I had mine all enabled. Disabling this checkbox corrects the 'frames out of sequence' issue I was whining about when stepping backwards thru clips. :)

Will disable this for all my cams and report my findings to Ken.
It may well be a known issue or not anything he can fix. (HW decoding on i7-4790 cpu...)
 
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