Configure VP9 tile-columns and tile-rows in FFmpeg

This article explains how to configure multi-threading in the FFmpeg libvpx-vp9 encoder using the -tile-columns and -tile-rows parameters. You will learn how these settings work, how to calculate the correct values for your video resolution, and how to apply them in your FFmpeg commands to speed up your encoding process.

Understanding VP9 Tiles

The VP9 video codec allows you to split a video frame into a grid of independent “tiles.” Because these tiles are independent of each other, the encoder can process them in parallel using multiple CPU threads, significantly reducing encoding time.

The parameters used to control this grid are -tile-columns and -tile-rows. These values are set on a log2 scale: * Number of columns = \(2^{\text{tile-columns}}\) * Number of rows = \(2^{\text{tile-rows}}\)

For example, setting -tile-columns 2 and -tile-rows 1 creates a grid of 4 columns (\(2^2\)) and 2 rows (\(2^1\)), resulting in 8 independent tiles.

Recommended Values by Resolution

VP9 has strict limitations on tile sizes to maintain compression efficiency. A single tile cannot be narrower than 256 pixels or wider than 4096 pixels.

Here are the standard recommended settings for common resolutions:

• 720p (1280x720):
  • -tile-columns 2 (4 columns)
  • -tile-rows 0 (1 row)
  • Total tiles: 4
• 1080p (1920x1080):
  • -tile-columns 2 (4 columns)
  • -tile-rows 1 (2 rows)
  • Total tiles: 8
• 4K (3840x2160):
  • -tile-columns 3 (8 columns)
  • -tile-rows 1 (2 rows)
  • Total tiles: 16

FFmpeg Command Example

To utilize tiling effectively, you must also enable multi-threading using the -threads parameter. The number of threads should ideally equal the total number of tiles you have created.

Here is a practical FFmpeg command for encoding a 1080p video:

ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 2M -tile-columns 2 -tile-rows 1 -threads 8 output.webm

In this command: * -tile-columns 2 splits the frame width into 4 columns. * -tile-rows 1 splits the frame height into 2 rows. * The total number of tiles is 8 (\(4 \times 2\)). * -threads 8 tells the encoder to spawn 8 threads to process the 8 tiles simultaneously.

Using more tiles than you have available CPU threads will not yield additional performance benefits. Additionally, using an excessive number of tiles can slightly degrade compression efficiency and visual quality, so only configure as many tiles as your hardware can actively process in parallel.