This article explains how different bitrate modes might affect video quality when livestreaming from a Videon device. The test case that was analyzed as a bench test for this article utilized an SRT output to a Videon-internal server that did not perform any transcoding. The resulting quality may vary on the individual combination of the endpoints and any additional transcoding after the stream leaves the device.
Key benefits
A higher configured bitrate does not always produce better video quality. During testing, a 7000 kbps constant bitrate (CBR) showed more visible quality issues than a 5500 kbps variable bitrate (VBR).
This means that increasing the bitrate alone may not resolve artifacts, loss of detail, or inconsistent image quality. The bitrate-control mode can be just as important as the configured bitrate setting.
With CBR, the encoder will attempt to maintain a consistent data rate. With variable bitrate, the encoder can allocate more data to visually complex scenes and less data to simpler scenes. Depending on the content and destination, VBR may preserve details more effectively even when its configured bitrate is lower.
Supported products
LiveEdge® Max, LiveEdge® Max 2, LiveEdge® Node.
When this may occur
Quality differences may be noticed when the video contains:
Fast motion or frequent camera movement
Transitions from still (static) slate graphics to highly dynamic video content
Fine textures, small text, or highly detailed backgrounds
Lighting changes, running water, or leaves in the wind
Similar behavior may appear with other combinations other than SRT and MWEdge. Additionally, other contributions may also affect streaming quality, such as how the streaming platform decodes or redistributes the video.
Requirements
Access to the device’s Web UI or LiveEdge® Cloud
A Videon device configured and ready for stream output
A valid stream destination and valid network connection
A way to review or record the stream at the output
Table of contents
Recommended configuration approach
When troubleshooting video quality, compare bitrate modes rather than just increasing the bitrate.
Start with the destination platform’s recommended resolution, framerate, codec, and bitrate range, if applicable.
Test the stream using VBR (by enabling Variable Bitrate Mode on all applicable video and audio encoders attached to the desired output) at a moderate bitrate.
Test the same content using CBR (by enabling Constant Bitrate Mode on all applicable video and audio encoders attached to the desired output) without changing any settings.
Compare the output from the final destination rather than the local preview.
Evaluate scenes with complex details such as high motion or highly detailed backgrounds immediately following something like a static slate graphic.
For example, if a 7000 kbps CBR stream is showing significantly more artifacting than a lower bitrate 5500 kbps VBR stream, adjust the VBR stream gradually instead. Do not assume increasing the CBR bitrate beyond 7000 kbps will fix the issue.
Troubleshooting
Symptom |
Likely cause |
Resolution |
| Image quality remains poor after increasing the bitrate | The selected rate-control mode may not suit the content | Compare VBR and CBR using the same source and destination |
| Motion looks blocky or loss of detail | The encoder may not be allocating enough data to complex frames | Test VBR and review the output from the destination platform |
| The stream quality becomes unstable at a higher bitrate | Available bandwidth may be insufficient | Lower the bitrate and verify the network capacity. |