Android MediaCodec: how to request a key frame when encoding - encode

Question

In Android4.1, a key frame is often requested in a real-time encoding application. But how to do it using MediaCodec object? The current Android4.2 SDK seems not support it.

Answer 1

You can produce random keyframe by specifying MediaCodec.BUFFER_FLAG_SYNC_FRAME when queuing input buffers:
MediaCodec codec = MediaCodec.createDecoderByType(type);
codec.configure(format, ...);
codec.start();
ByteBuffer[] inputBuffers = codec.getInputBuffers();
for (;;) {
int inputBufferIndex = codec.dequeueInputBuffer(timeoutUs);
if (inputBufferIndex >= 0) {
// fill inputBuffers[inputBufferIndex] with valid data
...
codec.queueInputBuffer(inputBufferIndex, 0, inputBuffers[inputBufferIndex].limit(), presentationTime,
isKeyFrame ? MediaCodec.BUFFER_FLAG_SYNC_FRAME : 0);
}
}
Stumbled upon the need to insert random keyframe when encoding video on Galaxy Nexus.
On it, MediaCodec didn't automatically produce keyframe at the start of the video.

Answer 2

MediaCodec has a method called setParameters which comes to the rescue.
In Kotlin you can do it like:
fun yieldKeyFrame(): Boolean {
val param = Bundle()
param.putInt(MediaCodec.PARAMETER_KEY_REQUEST_SYNC_FRAME, 0)
try {
videoEncoder.setParameters(param)
return true
} catch (e: IllegalStateException) {
return false
}
}
in above snippet, the videoEncoder is an instance of MediaCodec configured to encode.

Answer 3

You can request a periodic key frame by setting the KEY_I_FRAME_INTERVAL key when configuring the encoder. In the example below I am requesting one every two seconds. I've omitted the other keys like frame rate or color format for the sake of clarity, but you will still want to include them.
encoder = MediaCodec.createByCodecName(codecInfo.getName());
MediaFormat inputFormat = MediaFormat.createVideoFormat(mimeType, width, height);
/* ..... set various format options here ..... */
inputFormat.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, 2);
encoder.configure(inputFormat, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
encoder.start();
I suspect, however, that what you are really asking is how to request a random key frame while encoding, like at the start of a cut scene. Unfortunately I haven't seen an interface for that. It is possible that stopping and restarting the encoder would have the effect of creating a new key frame at the restart. When I have the opportunity to try that, I'll post the result here.
I hope this was helpful.
Thad Phetteplace - GLACI, Inc.