AV1 video: high level bitstream overview

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AV1 video high level bitstream overview
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AV1 video format overview

• AV1 is an open, royalty-free video codec
  developed by the Alliance for Open Media
  (AOMedia)
• Open and rayality-free, no licensing fees
• AV1 is open-source, with ongoing improvements
  driven by contributions from the industrys
  leading companies
• Targeted for modern video content optimized for
  4K, 8K, HDR (High dynamic range), and HFR (high
  frame rates)
• Used by YouTube, Netflix, and other major
  streaming services to deliver high-quality
  content with reduced bandwidth
• We will use Virinext Bitstream Analyzer for
  analyzing AV1 files.

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High level AV1 bitstream overview

• At the high level AV1 video is the sequence of
  Open Bitstream Units (OBUs)

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AV1 Open Bitstream Units (OBUs)

• There are different types of OBUs, including
• Sequence Header OBU Contains global parameters,
  such as color space, bit depth, and initial
  settings for the entire sequence
• Frame Header OBU Includes frame-specific details
  like resolution, coding tools, reference frames,
  and frame type
• Tile Group OBU Holds compressed data for one or
  more tiles within a frame
• Metadata OBU Provides auxiliary information,
  such as frame timing, HDR metadata, or
  scalability parameters.

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AV1 Sequence Header OBU

• The Sequence Header OBU contains global video
  parameters and typically appears at the start of
  the bitstream.
• Sequence Header OBU defines settings that apply
  to the entire sequence of frames, including
• Profile Specifies the encoding profile (e.g.,
  main, high)
• Level Defines the performance level for
  decoding, such as supported resolution and frame
  rate
• Bit depth Indicates the color depth (e.g.,
  8-bit, 10-bit)
• Color format Specifies the chroma subsampling
  (e.g., 420)
• Frame size Defines the dimensions of the video
  frames.

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AV1 Sequence Header OBU
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AV1 Frame Header OBU

• Frame Header OBU describes every frame in AV1
  bitstream.
• Frame Header OBU, which contains the information
  required to decode specific frame.
• Frame Header OBU includes a frame type field,
  which indicates whether the frame is a keyframe,
  intra-frame, or inter-frame.

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AV1 Tile Group OBU

• AV1 frames can be split into tiles.
• Tile is an independently encoded sections of a
  frame.
• Each tile contains its own compressed data and
  can be decoded independently from the others.
• Tiles can be used for parallel processing for
  improving encoding and decoding.

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AV1 video analysis with Virinext Bitstream
Analyzer

• Screenshot of frame preview, syntax viewer and
  GOP widgets of AV1 video file opened in Virinext
  Bitstream Analyzer

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References

• Virinext Bitsteam Analyzer - GUI tool for
  displaying and analyzing coded video and audio
  streams
• AV1 video high level bitstream overview
• AV1 homepage
• AV1 Bitstream Decoding Process Specification