Media gateway with overlay channels

A digital signal processor (DSP) embedded in a network media gateway, the DSP comprising:

• a receiver configured to receive overlay content data as rendered overlay content pixels;
• a memory buffer configured to store the received rendered overlay content pixels, each pixel being stored with the following information:
• a beginning coordinate pair of a pixel that represents the beginning of a row of pixels on which the pixel being stored is located,
• an offset from the beginning coordinate pair, and
• payload data that includes a luminance value Y, a red chrominance value Cr, a blue chrominance value Cb, and an alpha compositing value α particular to pixel being stored;
• and
• a processor configured to receive a first decoded video stream and mixes the first decoded video stream with the rendered overlay content pixels stored in the memory buffer, and to receive a different second decoded video stream and mix the second decoded video stream with the same overlay content pixels stored in the memory buffer.

A method implemented on a digital signal processor (DSP) of mixing rendered overlay content pixels stored in a memory buffer and a decoded video stream, thereby forming a encoded mixed stream, each pixel of the rendered overlay content pixels being stored with a beginning coordinate pair of a pixel that represents the beginning of a row of pixels on which the pixel being stored is located, an offset from the beginning coordinate pair, and payload data that includes a luminance value Yov, a red chrominance value Crov, a blue chrominance value Cbov, and an alpha compositing value α particular to the pixel being stored, the method comprising:

• performing, by the DSP, trans-sizing of the stored rendered overlay content pixels stored in the memory buffer based on a destination encoder channel;
• for each row of pixels stored in the memory buffer, mixing by the DSP the stored rendered overlay content pixels in the row and the pixels in corresponding rows of pixels in the decoded video stream to form a an encoded mixed stream according to the following equations:
• Ymix=Ydec*(1−α)+Yov*α,
• Cbmix=Cbdec*(1−α)+Cbov*α, and
• Crmix=Crdec*(1−α)+Crov*α, wherein
• Ymix, Cbmix, and Crmix are the luminance values, blue chrominance values, and red chrominance values, respectively, of the pixels in the encoded mixed stream, and Ydec, Cbdec, and Crdec are the luminance values, blue chrominance values, and red chrominance values, respectively, of the decoded video stream;
• and
• outputting, by the DSP, the encoded mixed stream.