1. mediacodec初始化

        try {
            mCodec = MediaCodec.createDecoderByType(mimeType);

            MediaCodecInfo codecInfo = mCodec.getCodecInfo();
            MediaCodecInfo.CodecCapabilities capabilities = codecInfo.getCapabilitiesForType(mimeType);

            MediaFormat format = MediaFormat.createVideoFormat(mimeType, width, height);
            mCodec.configure(format, null, null, 0);
            mCodec.start();
        } catch(Exception ex) {
            ex.printStackTrace();
        }

2. h264流输入及输出

public void inputBytes(byte[] frame, long ts) {

        try {
            int inputBufferIndex = mCodec.dequeueInputBuffer(0);

            if (inputBufferIndex >= 0) {
                ByteBuffer[] inputBuffers = mCodec.getInputBuffers();
                ByteBuffer buffer = inputBuffers[inputBufferIndex];
                buffer.clear();
                buffer.put(frame);
                mCodec.queueInputBuffer(inputBufferIndex, 0, frame.length, ts, 0);
            }

            MediaCodec.BufferInfo bufferInfo = new MediaCodec.BufferInfo();
            int outputBufferIndex = mCodec.dequeueOutputBuffer(bufferInfo, 0);

            while (outputBufferIndex >= 0) {

                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                    Image image = mCodec.getOutputImage(outputBufferIndex);
                    try {
                        imageToBitmap(image);
                    } catch(Exception ex) {
                        ex.printStackTrace();
                    } finally {
                        image.close();
                    }
                }

                mCodec.releaseOutputBuffer(outputBufferIndex, false);
                outputBufferIndex = mCodec.dequeueOutputBuffer(bufferInfo, 0);
            }

            if (outputBufferIndex == MediaCodec.INFO_TRY_AGAIN_LATER) {
                Log.d(TAG, "inputBytes: try later ..");
            } else if (outputBufferIndex == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
                Log.d(TAG, "inputBytes: BUFFERS_CHANGED");
            } else if (outputBufferIndex == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
                Log.d(TAG, "inputBytes: outputFormat " + mCodec.getOutputFormat());
            }
        } catch(Exception ex) {
            ex.printStackTrace();
        }
    }

3. getOutputImage中返回的是Image，为YUV_420_888， 需要转为NV21，然后通过YUVImage转为JPEG.

private static byte[] getDataFromImage(Image image) {
        Rect crop = image.getCropRect();
        int format = image.getFormat();
        int width = crop.width();
        int height = crop.height();
        Image.Plane[] planes = image.getPlanes();
        byte[] data = new byte[width * height * ImageFormat.getBitsPerPixel(format) / 8];
        byte[] rowData = new byte[planes[0].getRowStride()];

        int channelOffset = 0;
        int outputStride = 1;
        for (int i = 0; i < planes.length; i++) {
            switch (i) {
                case 0:
                    channelOffset = 0;
                    outputStride = 1;
                    break;
                case 1:
                    channelOffset = width * height + 1;
                    outputStride = 2;
                    break;
                case 2:
                    channelOffset = width * height;
                    outputStride = 2;
                    break;
            }
            ByteBuffer buffer = planes[i].getBuffer();
            int rowStride = planes[i].getRowStride();
            int pixelStride = planes[i].getPixelStride();
            int shift = (i == 0) ? 0 : 1;
            int w = width >> shift;
            int h = height >> shift;
            buffer.position(rowStride * (crop.top >> shift) + pixelStride * (crop.left >> shift));
            for (int row = 0; row < h; row++) {
                int length;
                if (pixelStride == 1 && outputStride == 1) {
                    length = w;
                    buffer.get(data, channelOffset, length);
                    channelOffset += length;
                } else {
                    length = (w - 1) * pixelStride + 1;
                    buffer.get(rowData, 0, length);
                    for (int col = 0; col < w; col++) {
                        data[channelOffset] = rowData[col * pixelStride];
                        channelOffset += outputStride;
                    }
                }
                if (row < h - 1) {
                    buffer.position(buffer.position() + rowStride - length);
                }
            }

        }
        return data;
    }

    Bitmap imageToBitmap(Image image) {
        Rect rect = image.getCropRect();
        YuvImage yuvImage = new YuvImage(getDataFromImage(image), ImageFormat.NV21, rect.width(),rect.height(), null);

        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        yuvImage.compressToJpeg(new Rect(0, 0, width, height), 100, stream);
        Bitmap bitmap = BitmapFactory.decodeByteArray(stream.toByteArray(), 0, stream.size());
        // saveBitmap(System.currentTimeMillis()+"", bitmap, mslict.getContext());
        try {
            stream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return bitmap;
    }