The video quality of a meeting varies depending on the available network bandwidth and on the number of participants. Video resolution is set through the Media Manager user policy settings. The information in this article provides a detailed description of the bandwidth requirements for each of the video resolution setting options. For addition information about Media Manager policy settings, see the Administration section of the Administering Sametime 9 product documentation.

Bandwidth requirement for a downlink from the Video MCU to the client

The Sametime® client can receive a maximum of six video streams. So depending on the number of participants in the conference, Sametime clients receive and send remote video streams that have different resolution, based on the bandwidth that is available.

Higher video resolution requires more bandwidth to produce the video. And the higher the bandwidth, the better the video quality. Sametime automatically adapts to the available bandwidth and reduces the bit-rate to a certain threshold for each chosen video resolution. However, the result may be a loss of quality if the available bandwidth becomes too low.

For example, if there are ten participants in the conference, the client can receive six remote video streams. With a line rate of 1024kbps, two streams will be at 180p@30fps (frames per second), and four will be at 180p@7.5fps. Tables 1-6 show the downlink resolution in frames per second (fps), based on the available bandwidth.

Table 1. Video Resolution for Six Video Streams.

Bit Rate	Downlink Resolution
1920kbps	180p@30fps x 6
1024kbps	180p@30fps x 2 + 180p@15fps x 4
768kbps	180p@15fps x 4 + 180p@7.5fps x 2
512kbps	180p@15fps x 5
384kbps	180p@15fps x 1 + 180p@7.5fps x 2
256kbps	180p@7.5fps x 2

Table 2. Video Resolution for Five Video Streams.

Bit Rate	Downlink Resolution
1920kbps	180p@30fps x 5
1024kbps	180p@30fps x 4 + 180p@15fps x 1
768kbps	180p@15fps x 5
512kbps	180p@7.5fps x 5
384kbps	180p@15fps x 1 + 180p@7.5fps x 2
256kbps	180p@7.5fps x 2

Table 3. Video Resolution for Four Video Streams.

Bit Rate	Downlink Resolution
1920kbps	360p@30fps x 4
1024kbps	180p@30fps x 4
768kbps	360p@15fps x 1 + 180p@15fps x 3
512kbps	180p@7.5fps x 4
384kbps	180p@15fps x 1 + 180p@7.5fps x 2
256kbps	180p@7.5fps x 2

Table 4. Video Resolution for Three Video Streams.

Bit Rate	Downlink Resolution
1920kbps	360p@30fps x 3
1024kbps	360p@30fps x 2 + 360p@15fps x 1
768kbps	180p@30fps x 3
512kbps	180p@15fps x 3
384kbps	180p@15fps x 1 + 180p@7.5fps x 2
256kbps	180p@7.5fps x 2

Table 5. Video Resolution for Two Video Streams.

Bit Rate	Downlink Resolution
1920kbps	360p@30fps x 2
1024kbps	360p@30fps x 2
768kbps	360p@30fps x 1 + 360p@15fps x 1
512kbps	180p@30fps x 2
384kbps	180p@15fps x 2
256kbps	180p@7.5fps x 2

Table 6. Video Resolution for One Video Stream.

Bit Rate	Downlink Resolution
1920kbps	720p@30fps x 1
1024kbps	720p@30fps x 1
768kbps	360p@30fps x 1
512kbps	360p@30fps x 1
384kbps	360p@30fps x 1
256kbps	360p@30fps x 1

Bandwidth requirement for an uplink from the client to the Video MCU

The Sametime client uses three temporal layers to stream video at different frame rates for each of the spatial resolutions of 180p, 360p and 720p. Table 7 shows the different speeds for each temporal layer.

Table 7. Temporal Layer Bandwidth Resolution.

Temporal Layer	Frames per Second	180p Resolution	360p Resolution	720p Resolution
Base layer	7.5fps	86kbps	173kbps	346kbps
First layer	15fps	128kbps	256kbps	512kbps
Second layer	30fps	192kbps	384kbps	768kbps

The Sametime client uses this temporal scalability to send multiple temporal layers of each resolution based on bandwidth available. As shown in Table 8, if 1024kbps are available, the client can send three streams of 180p@30fps, 360p@15fps, and 720p@15fps. However, to save bandwidth, the client sends a stream only if there is at least one remote client in the conference receiving it. So, for example, if no remote client is receiving 720p@15fps, then it is not sent. Only the streams 180p@30fps and 360p@15fps are sent.

Table 8. Uplink Resolutions.

Bit Rate	Uplink Resolution
1920kbps	180p@30fps + 360p@30fps + 720p@30fps
1024kbps	180p@30fps + 360p@15fps + 720p@15fps
768kbps	180p@30fps + 360p@30fps
512kbps	180p@30fps + 360p@15fps
384kbps	180p@15fps + 270p@15fps
256kbps	180p@30fps
128kbps	180p@7.5fps