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Get a frame and modify its data

Frames in MFormats SDK 

MFormats SDK is a frame-based framework which basically means "grab a frame, process the frame, output the frame". So you always work with frame objects (MFFrame). 

How to get frames with MPlatform SDK?

Frames in MPlatform SDK are MFrame objects. These objects support the IMFFrame interface of MFormats SDK (because they have the same core components). It means that you can convert an MFrame object to IMFFrame interface to call some specific method, for example, the MFPrint method.

There are several possibilities to get an MFrame object in MPlatform SDK.

ObjectFrameGet method

With this method, you can get the current frame processed by an object. Once this method is included in the IMObject interface, it is possible to get a frame from any object whether it is a source or a receiver.

MFrame myFrame;
(myPlaylist as IMObject).ObjectFrameGet(out myFrame);

FileFrameGet and FileFrameGetByTC methods

With these methods, you can get a frame from the desired position. The FileFrameGet returns you a frame by its position in seconds, and the FileFrameGetByTC returns you a frame by its timecode.

You can use these methods for objects that support the IMFile interface, i.e. MFile, MPlaylist, MMixer objects:

MFrame frameByPos;
(myPlaylist as IMFile).FileFrameGet(10.0, 0, out frameByPos);
MFrame frameByTC;
myTC.nHours := 10;
myTC.nMinutes := 23;
myTC.nSeconds := 45;
myTC.nFrames := 15;
(myPlaylist as IMFile).FileFrameGetByTC(ref myTC, out frameByTC);

OnFrame and OnFrameSafe events

With the events, you get access to every frame processed by an object. Here is an article about events.

How to modify a frame data?

Once a frame is received, you can get access to its data by addressing to the system memory. So you need to get a pointer to this data and a size of the data both for audio and for video.

You can do it using the FrameVideoGetBytes and the FrameAudioGetBytes methods in MPlatform SDK, and the MFVideoGetBytes and the MFAudioGetBytes methods in MFormats SDK.

FrameVideoGetBytes and MFVideoGetBytes methods return you a pointer to a video data and its size, so you can modify it using some external processing, for example, to draw on frames.

With FrameAudioGetBytes and MFAudioGetBytes methods, you get a pointer to an audio data and its size.

Note please that you should modify a frame data before the frame is sent to a receiver object. So with MFormats SDK, you should do all the modifications before you call the ReceiverFramePut method. And for MPlatform SDK, the best approach for this is using synchronous OnFrame (or OnFrameSafe) events. You can enable it with this code:

myFile.PropsSet("object::on_frame.sync", "true"); 
myFile.PropsSet("", "true"); 
myFile.OnFrameSafe += myFile_OnFrameSafe;

Then the frame, once processed within the OnFrameSafe event, is sent to an output object (for example, a preview or a renderer device).