A method comprising: receiving a first data stream (802, 1002) that represents a first video, wherein the first data stream includes a first sequence of frames that includes first intra-coded frames and first inter-coded frames; receiving a second data stream (804, 1004) that represents a second video, wherein the second data stream includes a second sequence of frames that includes at least second intra-coded frames, wherein the first video has a first frame rate that is higher than a second frame rate of the second video; inserting one or more second frames into the second data stream after each of the second intra-coded frames to make the frame rate of the second data stream with the inserted one or more second frames equivalent to the first frame rate and a key-frame interval of the first data stream and a key-frame interval of the second data stream with the inserted one or more second frames equivalent; and combining the received first data stream (802, 1002) and the received second data stream (804, 1004) having the inserted one or more second frames to obtain an output data stream (806, 1006) of encoded output frames, wherein combining the received first data stream (802, 1002) and the received second data stream having the inserted one or more second frames (804, 1004) comprises: combining each first intra-coded frame with a respective second intra-coded frame to obtain a respective intra-coded output frame within the output stream, and combining each first inter-coded frame with a respective second inter-coded frame of the second data stream with the inserted one or more second frames to obtain a respective inter-coded output frame within the output stream, wherein in each encoded output frame the respective first frame is vertically or horizontally stacked with the respective second frame. receiving a first data stream (802, 1002) that represents a first video, wherein the first data stream includes a first sequence of frames that includes first intra-coded frames and first inter-coded frames; receiving a second data stream (804, 1004) that represents a second video, wherein the second data stream includes a second sequence of frames that includes at least second intra-coded frames, wherein the first video has a first frame rate that is higher than a second frame rate of the second video; inserting one or more second frames into the second data stream after each of the second intra-coded frames to make the frame rate of the second data stream with the inserted one or more second frames equivalent to the first frame rate and a key-frame interval of the first data stream and a key-frame interval of the second data stream with the inserted one or more second frames equivalent; and combining the received first data stream (802, 1002) and the received second data stream (804, 1004) having the inserted one or more second frames to obtain an output data stream (806, 1006) of encoded output frames, wherein combining the received first data stream (802, 1002) and the received second data stream having the inserted one or more second frames (804, 1004) comprises: combining each first intra-coded frame with a respective second intra-coded frame to obtain a respective intra-coded output frame within the output stream, and combining each first inter-coded frame with a respective second inter-coded frame of the second data stream with the inserted one or more second frames to obtain a respective inter-coded output frame within the output stream, combining each first intra-coded frame with a respective second intra-coded frame to obtain a respective intra-coded output frame within the output stream, and combining each first inter-coded frame with a respective second inter-coded frame of the second data stream with the inserted one or more second frames to obtain a respective inter-coded output frame within the output stream, wherein in each encoded output frame the respective first frame is vertically or horizontally stacked with the respective second frame.