Automatically adjust video quality



Note: Automatic adjustment is applicable only to single-bit-rate encoding and to streaming using Flash Media Server. It is not applicable when encoding multi-bit rate streams or when saving to a file only.

Flash Media Live Encoder monitors the amount of data in the RTMP buffer and compares it to the maximum buffer size specified in the encoding profile.

Sometimes, the rate at which Flash Media Live Encoder streams media to Flash Media Server exceeds the rate at which the network can handle the data. This scenario happens if network latency is high or network bandwidth is lowered for some reason. Excess data is stored in the RTMP buffer. If the buffer value exceeds the maximum size specified in Auto Adjust settings, Flash Media Live Encoder can automatically adjust the video quality to ensure uninterrupted streaming.

Automatic adjustment applies only to video streams, with or without audio. It does not apply to audio-only streams.

During an encoding session, you can enable or disable automatic adjustment in the user interface but not in command-line mode. In command-line mode, enable or disable automatic adjustment before you start the encoding session.

To turn on automatic adjustment, select the Auto Adjust option in the Output panel. You can choose to degrade video quality or drop video frames.

Degrade quality

This setting degrades the quality of the video by reducing the bit rate until data can be streamed without exceeding the specified RTMP buffer size. This feature is not enabled by default.

Click the settings icon to configure the following quality settings:

  • Maximum buffer size. Once this value is exceeded, Flash Media Live Encoder enacts quality degradation. For higher bandwidth, use a higher number. For lower bandwidth, use a lower number.

  • Minimum video bit rate. The minimum acceptable bit rate at which to stream media. If network conditions deteriorate to the point that a lower bit rate is required to stream video, frame dropping is enabled.

  • Preserve per-frame quality. Reduces the frame rate to as low as 50% of the specified value.

Both the published stream and the saved output file reflect any quality degradation that takes place. Once the RTMP buffer value no longer exceeds the maximum value, Flash Media Live Encoder reapplies the values that were originally set in the encoding profile, in steps and as the network conditions allow.

Drop frames

This setting drops video frames from the RTMP buffer until data can stream without exceeding the RTMP buffer size. When Auto Adjust is enabled, Drop Frames is enabled by default.

Click the settings icon to configure the maximum buffer size. Once this value is exceeded, Flash Media Live Encoder starts dropping frames. For higher bandwidth, use a higher number. For lower bandwidth, use a lower number.

Dropping frames affects streaming video only. Subscribers usually notice when frames are dropped because the video appears jerky or appears to stutter.

Flash Media Live Encoder drops frames at intervals, rather than all at once. It drops backward-facing video frames between keyframes. For VP6 video, I-frames are dropped. For H.264 video, I-frames, B-frames, and P-frames may be dropped. If necessary, keyframes (VP6) or IDR frames (H.264) may also be dropped.

When the RTMP buffer size returns to a normal value, Flash Media Live Encoder stops dropping video frames.