问题
I'm implementing a camera application on Android devices. Currently, I use Camera2 API and ImageReader to get image data in YUV_420_888 format, but I don't know how to exactly write these data to MediaCodec.
Here are my questions:
- What is
YUV_420_888?
The format YUV_420_888 is ambiguous because it can be any format which belongs to the YUV420 family, such as YUV420P, YUV420PP, YUV420SP and YUV420PSP, right?
By accessing the image's three planes(#0, #1, #2), I can get the Y(#0), U(#1), V(#2) values of this image. But the arrangement of these values may not be the same on different devices. For example, if YUV_420_888 truly means YUV420P, the size of both Plane#1 and Plane#2 is a quarter of the size of Plane#0. If YUV_420_888 truly means YUV420SP, the size of both Plane#1 and Plane#2 is half of the size of Plane#0(Each of Plane#1 and Plane#2 contains U, V values).
If I want to write these data from image's three planes to MediaCodec, what kind of format I need to convert to? YUV420, NV21, NV12, ...?
- What is
COLOR_FormatYUV420Flexible?
The format COLOR_FormatYUV420Flexible is also ambiguous because it can be any format which belongs to the YUV420 family, right? If I set KEY_COLOR_FORMAT option of a MediaCodec object to COLOR_FormatYUV420Flexible, what format(YUV420P, YUV420SP...?) of data should I input to the MediaCodec object?
- How about using
COLOR_FormatSurface?
I know MediaCodec has its own surface, which can be used if I set KEY_COLOR_FORMAT option of a MediaCodec object to COLOR_FormatSurface. And with Camera2 API, I don't need to write any data by myself to the MediaCodec object. I can just drain the output buffer.
However, I need to change the image from the camera. For example, draw other pictures, write some text on it, or insert another video as POP(Picture of Picture).
Can I use ImageReader to read the image from Camera, and after re-drawing that, write the new data to MediaCodec's surface, and then drain it out? How to do that?
EDIT1
I implemented the function by using COLOR_FormatSurface and RenderScript. Here is my code:
onImageAvailable method:
public void onImageAvailable(ImageReader imageReader) {
try {
try (Image image = imageReader.acquireLatestImage()) {
if (image == null) {
return;
}
Image.Plane[] planes = image.getPlanes();
if (planes.length >= 3) {
ByteBuffer bufferY = planes[0].getBuffer();
ByteBuffer bufferU = planes[1].getBuffer();
ByteBuffer bufferV = planes[2].getBuffer();
int lengthY = bufferY.remaining();
int lengthU = bufferU.remaining();
int lengthV = bufferV.remaining();
byte[] dataYUV = new byte[lengthY + lengthU + lengthV];
bufferY.get(dataYUV, 0, lengthY);
bufferU.get(dataYUV, lengthY, lengthU);
bufferV.get(dataYUV, lengthY + lengthU, lengthV);
imageYUV = dataYUV;
}
}
} catch (final Exception ex) {
}
}
Convert YUV_420_888 to RGB:
public static Bitmap YUV_420_888_toRGBIntrinsics(Context context, int width, int height, byte[] yuv) {
RenderScript rs = RenderScript.create(context);
ScriptIntrinsicYuvToRGB yuvToRgbIntrinsic = ScriptIntrinsicYuvToRGB.create(rs, Element.U8_4(rs));
Type.Builder yuvType = new Type.Builder(rs, Element.U8(rs)).setX(yuv.length);
Allocation in = Allocation.createTyped(rs, yuvType.create(), Allocation.USAGE_SCRIPT);
Type.Builder rgbaType = new Type.Builder(rs, Element.RGBA_8888(rs)).setX(width).setY(height);
Allocation out = Allocation.createTyped(rs, rgbaType.create(), Allocation.USAGE_SCRIPT);
Bitmap bmpOut = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
in.copyFromUnchecked(yuv);
yuvToRgbIntrinsic.setInput(in);
yuvToRgbIntrinsic.forEach(out);
out.copyTo(bmpOut);
return bmpOut;
}
MediaCodec:
mediaFormat.setInteger(MediaFormat.KEY_COLOR_FORMAT, MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface);
...
mediaCodec.configure(mediaFormat, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
...
surface = mediaCodec.createInputSurface(); // This surface is not used in Camera APIv2. Camera APIv2 uses ImageReader's surface.
And in athother thread:
while (!stop) {
final byte[] image = imageYUV;
// Do some yuv computation
Bitmap bitmap = YUV_420_888_toRGBIntrinsics(getApplicationContext(), width, height, image);
Canvas canvas = surface.lockHardwareCanvas();
canvas.drawBitmap(bitmap, matrix, paint);
surface.unlockCanvasAndPost(canvas);
}
This way works, but the performance is not good. It can't output 30fps video files(only ~12fps). Perhaps I should not use COLOR_FormatSurface and the surface's canvas for encoding. The computed YUV data should be written to the mediaCodec directly without any surface doing any conversion. But I still don't know how to do that.
回答1:
You are right, YUV_420_888 is a format that can wrap different YUV 420 formats. The spec carefully explains that the arrangement of U and V planes is not prescribed, but there are certain restrictions; e.g. if the U plane has pixel stride 2, same applies to V (and then the underlying byte buffer can be NV21).
COLOR_FormatYUV420Flexible is a synonym of YUV_420_888, but they belong to different classes: MediaCodec and ImageFormat, respectively.
The spec explains:
All video codecs support flexible YUV 4:2:0 buffers since LOLLIPOP_MR1.
COLOR_FormatSurface is an opaque format that can deliver best performance for MediaCodec, but this comes at price: you cannot directly read or manipulate its content. If you need to manipulate the data that goes to the MediaCodec, then using ImageReader is an option; whether it will be more efficient than ByteBuffer, depends on what you do and how you do it. Note that for API 24+ you can work with both camera2 and MediaCodec in C++.
The invaluable resource of details for MediaCodec is http://www.bigflake.com/mediacodec. It references a full example of 264 encoding.
来源：https://stackoverflow.com/questions/46403934/how-to-correctly-use-imagereader-with-yuv-420-888-and-mediacodec-to-encode-video