Delayed duplicate I-picture for video coding

1. A method comprising:

selecting, by a video encoder, a first picture to be encoded as a first decoder refresh picture;

encoding the first picture in a compressed bit stream as the first decoder refresh picture;

selecting, by the video encoder, a second picture to be encoded as a delayed duplicate intra-predicted picture (DDI));

encoding, by the video encoder, the second picture in the compressed bit stream as an intra-predicted picture (I-picture) to generate the DDI, and storing the I-picture,

selecting, by the video encoder, a third picture to be encoded as a second decoder refresh picture; and

encoding the third picture in the compressed bit stream as the second decoder refresh picture using the stored I-picture as a reference picture.

2. The method of claim 1 , further comprising:

encoding the third picture as a P-picture in the compressed video bit stream.

3. The method of claim 1 , further comprising:

receiving the compressed bit stream in a video decoder; and

decoding the compressed bit stream in the video decoder to reconstruct the pictures, wherein decoding the compressed video bit stream comprises:

decoding the DDI, wherein the decoded picture is stored for use as a second reference picture for the encoded decoder refresh picture and wherein the decoded picture is not displayed;

decoding the encoded decoder refresh picture from the compressed video bit stream, wherein the second reference picture is used to reconstruct the decoder refresh picture; and

providing the decoded decoder refresh picture for display.

4. The method of claim 1 , wherein the DDI is encoded into a DDI bit stream that is transmitted separately from the compressed video bit stream.

5. The method of claim 4 , wherein the DDI bit stream is transmitted according to a first network protocol and the compressed video bit stream is transmitted according to a second network protocol.

6. The method of claim 4 , wherein the first network protocol and the second network protocol are a same network protocol.

7. The method of claim 1 , wherein the video encoder and a video decoder are comprised in a video conferencing system.

8. A system comprising:

a video encoder; and

a first network interface operatively coupled to the video encoder,

wherein the video encoder is configured to:

select a first picture to be encoded as a first decoder refresh picture;

encode the first picture in a compressed bit stream as the first decoder refresh picture;

select a second picture to be encoded as a delayed duplicate intra-predicted picture (DDI), wherein the picture would otherwise be encoded as an inter-predicted picture (P-picture);

encode the second picture as an intra-predicted picture (I-picture) in the compressed bit stream to generate the DDI, and store the I-picture;

select a third picture to be encoded as a second decoder refresh picture; and

encode the third picture in the compressed bit stream as the second decoder refresh picture using the stored I-picture as a reference picture.

9. The system of claim 8 , wherein the video encoder is configured to encode the third picture as a P-picture in the compressed video bit stream.

10. The method of claim 1 ,

wherein the third picture is selected as a number Z pictures after the first picture in a video sequence;

wherein the second picture is selected as a number N pictures before the third picture in the video sequence; and

wherein Z and N are predetermined numbers such that Z>N>1.

11. The method of claim 1 , further comprising:

transmitting the second decoder refresh picture to a video decoder in real time;

transmitting the I-picture to the video decoder as a delayed transmission in non-real time;

decoding, by the video decoder, the I-picture;

decoding, by the video decoder, the second decoder refresh picture using the decoded I-picture;

wherein the second picture is selected so that the I-picture will be received and decoded by the decoder before the video decoder begins decoding the second decoder refresh picture.

12. The system of claim 8 ,

wherein the third picture is selected as a number Z pictures after the first picture in a video sequence;

wherein the second picture is selected as a number N pictures before the third picture in the video sequence; and

wherein Z and N are predetermined numbers such that Z>N>1.

13. The system of claim 8 ,

wherein the network interface is configured to:

transmit the second decoder refresh picture to a video decoder in real time; and

transmit the I-picture to the video decoder as a delayed transmission in non-real time;

wherein the video decoder is configured to:

decode the I-picture; and

decode the second decoder refresh picture using the decoded I-picture; and

wherein the second picture is selected so that the I-picture will be received and decoded by the decoder before the video decoder begins decoding the second decoder refresh picture.