Experiment #2
- We measured a correlation between network bandwidth and video quality.
- Determines to dynamically change video quality, taking into account network bandwidth and number of participants.
- To ensure that video quality(choppy, distorted) is maintained when reducing video resolution as network bandwidth decreases.
- Concluded
- Result, As network bandwidth decreases, lowering the video resolution preserves video quality (choppy, distortion).
- default : bitrate ?, image resolution 640x480 pixel (laptop camera resolution), 30 fps
| Suggested bitrate settings | Use | Resolution |
|---|---|---|
| level 1 (ultra low) 50 kbps | O | 320 x 240 |
| level 2 (low) 120 kbps | O | 320 x 240 |
| level 3 (medium) 250 kbps | O | 480 x 360 |
| level 4 (high) 500 kbps | O | 640 x 480 |
| level 5 (ultra high) 1 Mbps | O | 640 x 480 |
- The table below shows the test results by changing the bandwidth by setting the bit rate for each resolution using the results of the above table.
| suggested bitrate | selected image resolution | required target bandwidth ((s. bitrate + 300) * 4) | 3 | 2 | 1 | 0.5 |
|---|---|---|---|---|---|---|
| 60 kbps | 320 x 240 | 1440 kbps | OK | OK | OK | OK |
| 120 kbps | 320 x 240 | 1680 kbps | OK | OK | OK | NG |
| 250 kbps | 480 x 360 | 2200 kbps | OK | OK | OK | NG |
| 500 kbps | 640 x 480 | 3200 kbps | OK | NG(△) | NG | NG |
| 1024 kbps | 640 x 480 | 5296 kbps | NG(△) | NG | NG | NG |
- required target bandwidth = (suggested bitrate + audio and header data size) x 4
- where, 4 means star topology
- In some items, some latency is added, so it is marked with (△).
- 500 kbps and bandwidth 2 Mbps
- 1024 kbps and bandwidth 3 Mbps
- 500 kbps and bandwidth 2 Mbps
- Also, the result of measuring the packet speed with wireshark is as follows.
- Although it is not accurately mapped to the limited bandwidth in the AP, it was confirmed that an issue occurred when the packet speed was slow.
| bitrate | resolution | 3 | 2 | 1 | 0.5 |
|---|---|---|---|---|---|
| 60 Kbps | 320x240 | 770 Kbps | 774 Kbps | 768 Kbps | 776 Kbps |
| 120 Kbps | 320x240 | 1010 Kbps | 1002 Kbps | 1011 Kbps | 1002 Kbps |
| 250 Kbps | 480x360 | 1603 Kbps | 1601 Kbps | 1601 Kbps | 1283 Kbps |
| 500 Kbps | 640x480 | 2647 Kbps | 2626 Kbps | 2263 Kbps | 1750 Kbps |
| 1024 Kbps | 640x480 | 4693 Kbps | 4364 Kbps | 3252 Kbps | 2788 Kbps |
- 2 laptops installed GStreamer CLI tool
- Raspberry Pi 4
- Scripts that can change Pi's the max bandwidth
- Transmit high quality video data using GStreamer CLI tool
- Reduce the available bandwidth on raspberry pi.
- Check video quality(choppy, distortion).
- Transmit video data with reduced quality using GStreamer.
- Check video quality(choppy, distortion).
- 1W
- gstreamer.freedesktop.org
- How to calculate optimal Bitrate from video resolution (https://rasdin.tistory.com/180)
- What Is the Best Bitrate Setting for H.264 Encoding
- Reference Table :
- We have to use 5GHz WIFI and 2.4GHz WIFI to utilize Rasberry PI4 Router as evaluation condition.
But the current Wework environment is limited to a very low bandwidth due to the congestion of the 2.4GHz band WIFI network. - Better to ask mentors about the evaluation environment and get their feedback.
