Encoding – MPEG-4 AVC (H.264) Controls - AWS Elemental Server

This is version 2.16 of the AWS Elemental Server documentation. This is the latest version. For prior versions, see the Previous Versions section of AWS Elemental Conductor File and AWS Elemental Server Documentation.

Encoding – MPEG-4 AVC (H.264) Controls

Description

A few h.264-specific controls are available on AWS Elemental systems that affect video quality:

  • CABAC: This control enables arithmetic coding and can compress the same data with ~15% fewer bits.

  • Slices: This control improves speed of encoding. Using a higher number of slices can improve speed optimization but results in slightly less quality.

  • Flicker Reduction: This control reduces flicker in the video. It enables an additional encoding algorithm that compensates for visual differences when I-frames have occurred (often referred to as I-frame "pop"). The AWS Elemental system uses this approach to encode I-frames as if they were P-frames (thus creating a "PI"-frame), identify macroblocks that are prone to flicker, merge pixels from the PI-frame for the flicker-prone MBs into the I-frame, and then encode the PI-frame. This method carries some of the visual quality from the end of one GOP to the start of the next GOP, preventing the abrupt change in detail that gives the effect of a flicker in the video.

  • Reference Frames: This control defines the number of frames that can be used to define B- and P- frames.

Recommendations

  • Use High Profile with H.264 to improve quality over Baseline Profile and Main Profile.

  • Always enable CABAC unless the intended decoder or playback device doesn't support it.

  • Set Slices to 2 (or higher) for all HD resolution outputs or high bitrate outputs. (AWS Elemental presets typically use 2 slices for 720p content and 4 slices for 1080p content.) For resolutions below 720p, set Slices to 1.

  • Set Flicker Reduction to "high" for low-motion content. Disable it for high-motion content.

  • Set Reference Frames to 2 or more for flash compensation.

Location of Fields

Location of Field on Web Interface Location of Tag in XML
Streams – Video > Advanced > Profile stream_assembly/video_description/h264_settings>/cabac
Streams – Video > Advanced > Level stream_assembly/video_description/h264_settings>/level
Streams – Video > Advanced > CABAC stream_assembly/video_description/h264_settings>/cabac
Streams – Video > Advanced > Slices stream_assembly/video_description/h264_settings/slices
Streams – Video > Advanced > Flicker Reduction stream_assembly/video_description/h264_settings/flicker_reduction