Options

The filter accepts the following options, any of the options supported by the libswscale scaler, as well as any of the framesync options.

See the ffmpeg-scaler manual for the complete list of scaler options.

width, w, height, h

Set the output video dimension expression. Default value is the input dimension.

If the width or w value is 0, the input width is used for the output. If the height or h value is 0, the input height is used for the output.

If one and only one of the values is -n with n >= 1, the scale filter will use a value that maintains the aspect ratio of the input image, calculated from the other specified dimension. After that it will, however, make sure that the calculated dimension is divisible by n and adjust the value if necessary.

If both values are -n with n >= 1, the behavior will be identical to both values being set to 0 as previously detailed.

See below for the list of accepted constants for use in the dimension expression.

eval

Specify when to evaluate width and height expression. It accepts the following values:

init

Only evaluate expressions once during the filter initialization or when a command is processed.

frame

Evaluate expressions for each incoming frame.

Default value is init.

interl

Set the interlacing mode. It accepts the following values:

1

Force interlaced aware scaling.

0

Do not apply interlaced scaling.

-1

Select interlaced aware scaling depending on whether the source frames are flagged as interlaced or not.

Default value is 0.

flags

Set libswscale scaling flags. See the ffmpeg-scaler manual for the complete list of values. If not explicitly specified the filter applies the default flags.

param0, param1

Set libswscale input parameters for scaling algorithms that need them. See the ffmpeg-scaler manual for the complete documentation. If not explicitly specified the filter applies empty parameters.

size, s

Set the video size. For the syntax of this option, check the "Video size" section in the ffmpeg-utils manual.

in_color_matrix, out_color_matrix

Set in/output YCbCr color space type.

This allows the autodetected value to be overridden as well as allows forcing a specific value used for the output and encoder.

If not specified, the color space type depends on the pixel format.

Possible values:

auto

Choose automatically.

bt709

Format conforming to International Telecommunication Union (ITU) Recommendation BT.709.

fcc

Set color space conforming to the United States Federal Communications Commission (FCC) Code of Federal Regulations (CFR) Title 47 (2003) 73.682 (a).

bt601, bt470, smpte170m

Set color space conforming to:

• ITU Radiocommunication Sector (ITU-R) Recommendation BT.601

• ITU-R Rec. BT.470-6 (1998) Systems B, B1, and G

• Society of Motion Picture and Television Engineers (SMPTE) ST 170:2004

smpte240m

Set color space conforming to SMPTE ST 240:1999.

bt2020

Set color space conforming to ITU-R BT.2020 non-constant luminance system.

in_range, out_range

Set in/output YCbCr sample range.

This allows the autodetected value to be overridden as well as allows forcing a specific value used for the output and encoder. If not specified, the range depends on the pixel format. Possible values:

auto/unknown

Choose automatically.

jpeg/full/pc

Set full range (0-255 in case of 8-bit luma).

mpeg/limited/tv

Set "MPEG" range (16-235 in case of 8-bit luma).

in_chroma_loc, out_chroma_loc

Set in/output chroma sample location. If not specified, center-sited chroma is used by default. Possible values:

• auto, unknown
• left
• center
• topleft
• top
• bottomleft
• bottom

force_original_aspect_ratio

Enable decreasing or increasing output video width or height if necessary to keep the original aspect ratio. Possible values:

disable

Scale the video as specified and disable this feature.

decrease

The output video dimensions will automatically be decreased if needed.

increase

The output video dimensions will automatically be increased if needed.

One useful instance of this option is that when you know a specific device’s maximum allowed resolution, you can use this to limit the output video to that, while retaining the aspect ratio. For example, device A allows 1280x720 playback, and your video is 1920x800. Using this option (set it to decrease) and specifying 1280x720 to the command line makes the output 1280x533.

Please note that this is a different thing than specifying -1 for w or h, you still need to specify the output resolution for this option to work.

force_divisible_by

Ensures that both the output dimensions, width and height, are divisible by the given integer when used together with force_original_aspect_ratio. This works similar to using -n in the w and h options.

This option respects the value set for force_original_aspect_ratio, increasing or decreasing the resolution accordingly. The video’s aspect ratio may be slightly modified.

This option can be handy if you need to have a video fit within or exceed a defined resolution using force_original_aspect_ratio but also have encoder restrictions on width or height divisibility.

The values of the w and h options are expressions containing the following constants:

in_w, in_h

The input width and height

iw, ih

These are the same as in_w and in_h.

out_w, out_h

The output (scaled) width and height

ow, oh

These are the same as out_w and out_h

a

The same as iw / ih

sar

input sample aspect ratio

dar

The input display aspect ratio. Calculated from (iw / ih) * sar.

hsub, vsub

horizontal and vertical input chroma subsample values. For example for the pixel format "yuv422p" hsub is 2 and vsub is 1.

ohsub, ovsub

horizontal and vertical output chroma subsample values. For example for the pixel format "yuv422p" hsub is 2 and vsub is 1.

n

The (sequential) number of the input frame, starting from 0. Only available with eval=frame.

t

The presentation timestamp of the input frame, expressed as a number of seconds. Only available with eval=frame.

pos

The position (byte offset) of the frame in the input stream, or NaN if this information is unavailable and/or meaningless (for example in case of synthetic video). Only available with eval=frame. Deprecated, do not use.

ref_w, rw, ref_h, rh, ref_a, ref_dar, rdar, ref_n, ref_t, ref_pos

Eqvuialent to the above, but for a second reference input. If any of these variables are present, this filter accepts two inputs.

Commands

This filter supports the following commands:

width, w, height, h

Set the output video dimension expression. The command accepts the same syntax of the corresponding option.

If the specified expression is not valid, it is kept at its current value.