Video resolution requirements
The video quality of a meeting varies depending on the available network bandwidth and on the number of participants. 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.
Bandwidth requirement for a downlink from the Video MCU to the client
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.
Bit Rate | Downlink Resolution | Total Displayed Videos |
---|---|---|
1920kbps | 180p@30fps x 6 | 6 |
1024kbps | 180p@30fps x 2 + 180p@15fps x 4 |
6 |
768kbps | 180p@15fps x 4 + 180p@7.5fps x 2 |
6 |
512kbps | 180p@15fps x 5 | 5 |
384kbps | 180p@15fps x 1 + 180p@7.5fps x 2 |
3 |
256kbps | 180p@7.5fps x 2 | 2 |
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 |
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 |
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 |
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 |
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.
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.
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 |