AV1 Interlaced Video Support Explained

This article examines how the AV1 video codec manages legacy interlaced content and addresses whether progressive scanning is strictly required. Unlike older broadcast standards such as MPEG-2 and H.264, AV1 completely omits native interlaced field coding from its specification, making progressive scanning mandatory for all encoded video streams.

The Removal of Interlaced Support

The Alliance for Open Media (AOMedia) designed AV1 primarily for modern web streaming, computer monitors, mobile devices, and contemporary televisions, none of which utilize interlaced display technology. Older codecs like MPEG-2 and H.264 (AVC) included dedicated, complex toolsets—such as Picture-Adaptive Frame-Field (PAFF) and Macroblock-Adaptive Frame-Field (MBAFF) coding—to split frames into alternating odd and even field pairs.

AV1 strips away all legacy field-coding syntax entirely. The bitstream specification contains no mechanisms to identify, signal, or decode separate fields. Every frame passed into an AV1 encoder is processed, compressed, and output as a single, unified progressive picture.

How to Handle Interlaced Footage with AV1

Because AV1 does not accept raw interlaced fields natively, any legacy interlaced source material (such as 480i, 576i, or 1080i broadcast recordings) must be deinterlaced before encoding:

  1. Pre-Encoding Deinterlacing: Video processors must convert interlaced fields into full progressive frames in a pre-processing pipeline. Modern software filters—such as Yadif, BWDIF, or neural-network-driven deinterlacers like QTGMC—reconstruct missing lines and reduce combing artifacts prior to delivering the frames to the AV1 encoder.
  2. Frame Rate Adaptation: Converting interlaced video to progressive typically involves either maintaining the nominal frame rate (e.g., converting 1080i at 29.97 frames per second to 1080p at 29.97 fps) or bob-deinterlacing to match the temporal field rate (e.g., converting 1080i at 59.94 fields per second to a smooth 1080p at 59.94 full fps).

Attempting to feed interlaced video directly into an AV1 encoder without deinterlacing will cause the encoder to treat the interlaced combing artifacts as sharp, high-frequency image details. This severely degrades compression efficiency, consumes an excessive amount of bitrate, and results in visible visual defects during playback.

Progressive scanning is strictly required by the AV1 specification. Hardware decoders and playback software assume that all incoming AV1 data represents progressive content, eliminating the hardware overhead and computational complexity required to support legacy interlaced television standards.