Reverse Playback with AV Foundation

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giodev
Posts: 10
Joined: Fri May 01, 2015 8:35 am

Reverse Playback with AV Foundation

Post by giodev » Thu Sep 10, 2015 10:38 am

Hi guys,

Part of the application that I'm developing requires a video to be able to play backwards, the main target platform is Windows were it works as expected, however there is a call for the program on Mac as well, where it currently doesn't. I'm aware that QuickTime has been replaced with AV Foundation for the implementation on Mac, but obviously I need to figure something out here!

Basically my question boils down to two parts:
1) Is there a way to play a video backwards on Mac that I don't know about? (I've thought about repeatedly stepping back 1 frame X times a second, where X is the frame rate of the video, but I imagine that will kill performance)
2) I believe that in direct Mac development in C++, reverse playback with AV Foundation is possible, so are there plans to include that in a future version of LiveCode?

I'm kind of assuming that the second question is only answerable by devs, unless there is a roadmap for development that I haven't seen.

Anyway, any response would be good, thanks for reading!

Klaus
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Joined: Sat Apr 08, 2006 8:41 am
Location: Germany
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Re: Reverse Playback with AV Foundation

Post by Klaus » Thu Sep 10, 2015 12:23 pm

Hi giodev,

yep, that's possible, check "playrate" in the dictionary!
Setting this to a negative number will play the video backwards.


Best

Klaus

LiveCode_Panos
Livecode Staff Member
Livecode Staff Member
Posts: 612
Joined: Fri Feb 06, 2015 4:03 pm

Re: Reverse Playback with AV Foundation

Post by LiveCode_Panos » Thu Sep 10, 2015 12:52 pm

Hi giodev,

As Klaus pointed out, you can use the 'playrate' property of the player object. In short:

play player 1 --> sets the playrate to 1 and plays the video forward
stop player 1 --> sets the playrate to 0 and stops playback
set the playrate of player 1 to -1 --> plays the video backwards

Best,
Panos
--

giodev
Posts: 10
Joined: Fri May 01, 2015 8:35 am

Re: Reverse Playback with AV Foundation

Post by giodev » Fri Sep 11, 2015 9:27 am

Hi guys, thanks for the quick responses!

I was already setting the playRate property to -1 and playing. The problem was (which as far as I can see in the Dictionary is undocumented) that I was following setting the playRate with starting the player, i.e.:

set the playRate of player "Player" to -1
start player "Player"

The above will make the player play forwards, which to me is not intuitive, but I can sort of understand why it does so.
I think updating the Dictionary for the start keyword to point out that it resets the playRate would be a good idea, and probably another amendment to say that setting the playRate will start the player as well.

Anyway, thanks, removed the line and we're back in business.

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