Encoding – Rate Control - AWS Elemental Live

This is version 2.18 of the AWS Elemental Live documentation. This is the latest version. For prior versions, see the Previous Versions section of AWS Elemental Live and AWS Elemental Statmux Documentation.

Encoding – Rate Control

Description

For AWS Elemental Live encoding, a buffer model (such as VBV or HRD) is used to manage rate control. The buffer model is a conceptual model for specifying both short-term and long-term constraints on encoding stream bitrates. The concept is that bits flow into the buffer at a fixed rate and picture are extracted instantaneously. In a "compliant" stream, the buffer cannot overflow or underflow. The following are several settings that allow the user to adjust the rate control settings tied to this buffer model:

  • Bitrate: Defines the long-term average bitrate, in bits/second. This field does not appear when Rate Control Mode is set to CQ.

  • Buffer Size: Defines the total buffer size in bits.

  • Max Bitrate: Defines the buffer fill rate, in bits/second. This field appears only when Rate Control Mode is set to VBR or Statmux.

  • Initial Buffer Fill: Defines the percentage of the buffer filled with bits before the decode begins.

These fields work with the Rate Control Mode field, which is discussed in Encoding – Rate Control Modes.

Recommendations

  • For Bitrate, more is better. The value used will depend more on other workflow constraints and will likely be different for each application.

  • In general, Buffer Size is commonly set to 1x to 2x the bitrate (again, more is typically better).

  • Max Bitrate is commonly set to 1x to 2x the bitrate. Although more is typically better, this value must also fit within the other encoding requirements of your specific application.

  • For Initial Buffer Fill, the default value (90%) typically provides the best video quality, so leave it blank to use the default.

Location of Fields

Location of Field on Web Interface Location of Tag in XML
Streams – Video > Advanced > Bitrate

stream_assembly/video_description/codec/bitrate

where codec is one of the following:

  • h264_settings

  • vc1_settings

  • mpeg2_settings

  • h265_settings

Streams – Video > Advanced > Buffer Size

stream_assembly/video_description/codec/buf_size

where codec is one of the following:

  • h264_settings

  • vc1_settings

  • mpeg2_settings

  • h265_settings

Streams – Video > Advanced > Max Bitrate

stream_assembly/video_description/codec/max_bitrate

where codec is one of the following:

  • h264_settings

  • vc1_settings

  • mpeg2_settings

  • h265_settings

Streams – Video > Advanced > Initial Buffer Fill

stream_assembly/video_description/codec/buf_fill_pct

where codec is one of the following:

  • h264_settings

  • vc1_settings

  • mpeg2_settings

  • h265_settings