H.264 Timeshift recordings

Hi all,

I have a request for the forum - Can anyone suggest the best option to solve an interesting problem I have. I want to record HD/SD signal onto a laptop - most likely in H.264 format. But what I want to be able to do is timeshift the recording and scrub back along the timeline to review previous events, whilst still recording. It's something similar to a PVR - however I don't want to use a PVR, I want a Windows PC based solution.

Thanks in advance

Doug

So,

It seems noone has tried this, I emailed Blackmagic support - they said they'd pass it on to the development team and see if it's something they can help with.

Does anyone think it's possible to develop something using the SDK?

Thanks again

Doug

You might want to try emailing the Developer List: http://lists.blackmagic-design.com/mail ... -developer

I'm surprised no-one on the BMD Developer List could help you. As it is one of the first things any Decklink developer is likely to develop as a test toy.

It's really a very simple thing to do - any windows developer can do this for you in a week or so.

Here is a basic spec:

On a "cheap as chips" Windows PC, i3 or i5, make sure you get a decent spinning magnetic disc, I really like WD Velocipraptors, but really any modern 7200rpm disc will do.

You then need two applications, or one application managing 4-6 Directshow graphs.

Capture Graph: captures from Decklink / Intensity / 1/2MEs, havbe VMR9 preview if you want to monitor your capture stream in this graph, but terminate both Audio and Video on a GMF Bridge Sink.

On the other side of the GMF Bridge prepare a Decklink MJPEG -> AVI MUX -> File, and send the Audio directly to the AVI Muxer as PCM. The trick is to prepare a 2nd record graph ready to swap over at a moments notice, increment the File ID.

Now when you start the graph you are recording to file 1. the moment you want to review, you "Swap" to record Graph2, and Close the file being recorded on Graph one.

You repeat this every time you want to go grab the next chunk that has been recorded.

You end up with a bunch of files in a directory, one always unavaiable as it is being recorded.

Whenever not actually recording a file, your second application is monitoring the directory the files already recorded, and is using a GMF Bridge again to stick the files back together and allow them to be navigated as one.

Tie the playback application up to a 2nd Decklink card, and you have instant replay.

It's less than 200 lines of code to make a basic system, and most of it is already done for you in the Decklink Sample SDK files.

Read about the GMF Bridge:

http://www.gdcl.co.uk/gmfbridge/

Good Luck with your project.

John