Recording and simultaneous playback on Decklink

[Callum Mclay]

Hi Terry

Please forgive if I am not quite getting at what it is you are trying to do, but basically the Decklink card works in either a capture or playback mode. When you are capturing, the card has a video pass through, and so on the outputs you will see a mirror of your input video. So while capturing, you cannot output a second video stream from the card.

In playback mode, the input is effectively disabled, allowing you to output your video stream on the different outputs, depending on which card you have.

I’m not quite sure how you are capturing/playing back your footage, so if you could give me a little more information on your workflow that would be great. Are you playing back the file you capture in Media Express? And it won’t play in Media Player?

During capture, it is down to the capture application to handle the video. Most capture applications, like our Media Express, or Adobe Premiere Pro capture only one video file and save it to disk, while displaying a desktop video preview.

You will need a custom application, that can accept a DirectShow video input, record the file, AND pass the video or allow the file to be played while it is being written. to another application ie Media Player, or it’s own custom player etc.

Please get back to me with a bit more information, and I will do my best to help out.

Callum McLay
Technical Support Consultant
Blackmagic Design EMEA

[David Curle]

PlayBox Technology’s “CaptureBox using Decklink allows you to both edit and playback files that are still capturing. – This is amazing for the broadcast industry – especially bsports or for those wanting to remove unrelated comercials. New comercials can be droped into the PlayBox Playlist where the old ones were deleted- all while stil recording.
cheers
David Curle (Ex PlayBox)

[Terry Philips]

Hi Callum

Thanks for responding. Let me explain my current non-Decklink workflow which I’m seeking to replicate with Decklink.

I capture an MPEG video. While the MPEG is still capturing, I copy that MPEG to another part of the hard drive. I then play out that new MPEG, embedded into my own custom application, by recording the video-out of my graphics card – which shows my desktop. My desktop is showing my custom application – the copied MPEG embedded in its customised graphical skin.

The application requires the video to be played in media player as part of the embed. The purpose of the application (in case you’re wondering, not that it matters) is to play out specialised time sensitive graphics synchronised with video.

A few minutes later I can go back to the recording file and copy it again. The intention therefore is to replay the video inside the graphics shell without disrupting the original recording more than necessary.

It works fine with an analogue MPEG capture box but I would like to do it in SDI. So I need to find a way of copying the avi file before the recording has completed. Recording an MJPEG in media express requires that the recording be ended before the file becomes usable, which means any copy taken before recoding ended is similarly unusable. What I’m after is either a fix which makes such a file usable or a different way of recording decklink SDI input that will allow the copied file to be played even though it’s copied before recording has ended.

Many thanks

Terry

[Terry Philips]

Thanks David

Will investigate