Encoding Cheatsheet

This is a cheatsheet for encoding best practices for VFX/Animation production. For each section there are more detailed sections on why these settings are picked, and notes on what parameters you may want to change.

This document is based on results from ffmpeg 6.0.

H264 Encoding from an image sequence for Web Review

If you are encoding from an image sequence (e.g. imagefile.0000.png imagefile.0001.png …) to h264 using ffmpeg, we recommend:

ffmpeg -r 24 -start_number 1 -i inputfile.%04d.png -pix_fmt yuv420p \
        -vf "scale=in_color_matrix=bt709:out_color_matrix=bt709" \
        -frames:v 100 -c:v libx264 -preset slower \
        -color_range tv -colorspace bt709 -color_primaries bt709 -color_trc iec61966-2-1 \
       -movflags faststart outputfile.mp4

-r 24	means 24 frames per second for the png files.
-start_number 1	The frame sequence starts from frame 1 (defaults to 0)
-i inputfile.%04d.png	the %04d means the file sequence will be padded to 4 digits, i.e. 0000, 0001, 0002, etc. It is the same syntax supported by the C printf function.
-frames:v 100	is optional, but allows you to specify how many frames to encode, otherwise it will encode the entire frame range. There is an obsolete alias flag -vframes which will be retired.
-c:v libx264	use the h264 encoding library (libx264)
-preset slower	a reasonably high quality preset, which will run slow, but not terribly slow.
-pix_fmt yuv420p	use yuv420 video format, which is typical for web playback. If you want a better quality for RV or other desktop tools use -pix_fmt yuv444p10le
-color_range tv	mp4 metadata - specifying color range as 16-235 (which is default for web playback).
-colorspace bt709	mp4 metadata - specifying bt709 yuv color pixel format
-color_primaries bt709	mp4 metadata - bt709 color gamut primaries
-color_trc iec61966-2-1	mp4 metadata color transfer = iec61966-2-1 = sRGB - See tests here. In some cases, you may also want -color_trc bt709
-movflags faststart	This re-organises the mp4 file, so that it doesnt have to read the whole file to start playback, useful for streaming. It can add a second or so to do this, since it does require re-writing the file.

-vf “scale=in_color_matrix=bt709:out_color_matrix=bt709” means use the sw-scale filter, setting:

in_color_matrix=bt709	color space bt709 video coming in (normal for TV/Desktop video).
out_color_matrix=bt709	means color space bt709 video going out.

The combination of this and in_color_matrix will mean the color encoding will match the source media. If you are only adding one set of flags, this is the one, otherwise it will default to an output colorspace of bt601, which is a standard definition spec from the last century, and not suitable for sRGB or HD displays.

Separately, if you are converting from exr’s in other colorspaces, please use OCIO to do the color space conversions. oiiotool is an excellent open-source tool for this.

For more details see:

• H264 Encoding
• YUV Conversion
• Browser color issues

ProRes 422 encoding with ffmpeg.

Unlike h264 and DnXHD, Prores is a reverse-engineered codec. However, in many cases ffmpeg can produce adequate results. There are a number of codecs, we recommend the prores_ks one.

ffmpeg -r 24 -start_number 1 -i inputfile.%04d.png \
    -pix_fmt yuv422p10le -vframes 100 \
    -c:v prores_ks -profile:v 3 -qscale:v 9 \
    -vf scale=in_color_matrix=bt709:out_color_matrix=bt709 outputfile.mov

-profile:v 3	Prores profile
-qscale:v 9	Controls the output quality, lower numbers higher quality and larger file-size. See comparison graph
-pix_fmt yuv422p10le	Convert to 10-bit YUV 422
-vendor apl0	Treat the file as if it was created by the apple-Prores encoder (even though it isn’t), helps some tools correctly read the Quicktime

For more details see:

• Prores
• YUV Conversion

ProRes 4444 encoding with ffmpeg.

As above, but using 4444 (i.e. a color value for each pixel + an alpha)

ffmpeg -r 24 -start_number 1 -i inputfile.%04d.png  \
    -pix_fmt yuv444p10le -vframes 100 \
   -c:v prores_ks -profile:v 4444 -qscale:v 9 \
   -vf scale=in_color_matrix=bt709:out_color_matrix=bt709 outputfile.mov

-profile:v 4444	Prores profile for 4444
-qscale:v 9	Controls the output quality, lower numbers higher quality and larger file-size. See comparison graph
-pix_fmt yuv444p10le	Convert to 10-bit YUV 4444

For more details see:

• Prores
• YUV Conversion

TV vs. Full range.

All the video formats typically do not use the full numeric range but instead the R’, B’, G’ and Y’ (luminance) channel have a nominal range of [16..235] and the CB and CR channels have a nominal range of [16..240] with 128 as the neutral value. This frequently results in quantisation artifacts for 8-bit encoding (the standard for web playback).

TODO Get Quantization examples.

You can force the encoding to be full range using the libswscale library by using

-vf "scale=in_range=full:in_color_matrix=bt709:out_range=full:out_color_matrix=bt709"

Specifying out_range=full forces the output range, but you also need to set the NCLX tag:

-color_range 2

A full example encode would look like:

ffmpeg -y -loop 1 -i ../sourceimages/radialgrad.png \
    -pix_fmt yuv420p -vf "scale=in_range=full:in_color_matrix=bt709:out_range=full:out_color_matrix=bt709" \
    -c:v libx264 -t 5  -qscale:v 1 \
    -color_range pc -colorspace bt709 -color_primaries bt709 -color_trc iec61966-2-1 ./greyramp-fulltv/radialgrad-full.mp4

We have seen the full range encoding work across all browsers, and a number of players including RV.

TODO: Do additional testing across all players.

For more details see:

• Comparing full-range vs. tv range
• Encoding Guide

Encoding as RGB.

You do not have to encode into YCrCb, h264 does support RGB encoding, which may be preferable in some situations.

Using the encoder:

-c:v libx264rgb

Will skip the conversion completely. Sadly this has no support in web browsers, but is supported by some players (e.g. RV). It is also limited to 8-bit.

TODO Check about 10-bit encoding.

For more details see:

• Comparing full-range vs. tv range
• Encoding Guide