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EncodeProres.md

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layout default
nav_order 4.2
title Prores Encoding
parent Encoding

ProRes

There are four Prores encoders, Prores, Prores_ks, Prores_aw and now with ffmpeg 5 VideoToolBox Prores, which is a hardware based OSX M1 encoder/decoder.

From https://trac.ffmpeg.org/wiki/Encode/VFX the recommendation is to use Prores_ks with -profile:v 3 and the qscale of 11

Options that can be used include:

-profile:v values can be one of.

  • proxy (0)
  • lt (1)
  • standard (2)
  • hq (3)
  • 4444 (4)
  • 4444xq (5)

-qscale:v between values of 9 - 13 give a good result, 0 being best, see below for some wedge tests.

-vendor apl0 - tricks the codec into believing its from an Apple codec.

Example encode would look like:

ffmpeg -r 24 -start_number 1 -i inputfile.%04d.png -vf "scale=in_color_matrix=bt709:out_color_matrix=bt709" \
        -vframes 100 -c:v prores_ks -profile:v 3 -pix_fmt yuv422p10le \
        -color_range tv -colorspace bt709 -color_primaries bt709 -color_trc iec61966-2-1 outputfile.mov

Using this with the usual color space flags, seems to work well with the exception of ffmpeg itself is unable to read a prores file, and convert it to a still frame. It needs the flags:-vf scale=in_color_matrix=bt709:out_color_matrix=bt709 added to the command to ensure the right input colorspace is recognised, e.g.:

ffmpeg -i INPUTFILE.mov -compression_level 10 -pred mixed -pix_fmt rgba64be \
   -sws_flags spline+accurate_rnd+full_chroma_int -vframes 1 \
   -vf scale=in_color_matrix=bt709:out_color_matrix=bt709 OUTPUTFILE.png

However, other encoders seem to be recognised correctly, so there is clearly some metadata missing. I did try using the prores_metadata filter to try adding some additional parameters, but it didn't seem to help.

ffmpeg -i ./chip-chart-yuvconvert/basicnclc.mov -c copy \
   -bsf:v prores_metadata=color_primaries=bt709:color_trc=bt709:colorspace=bt709 \
   chip-chart-yuvconvert/basicnclcmetadata.mov

If you are on a OSX M1 machine and are using ffmpeg 5.0 or higher, you can use the built in libraries to encode to prores using:

ffmpeg -r 24 -start_number 1 -i inputfile.%04d.png -vf "scale=in_color_matrix=bt709:out_color_matrix=bt709" \
        -vframes 100 -c:v prores_videotoolbox -profile:v 3 -pix_fmt yuv422p \
        -color_range tv -colorspace bt709 -color_primaries bt709 -color_trc bt709 outputfile.mp4

NOTE, it does not appear to allow -color_trc iec61966-2-1 (sRGB) -- so this needs more testing.

Prores_ks -qscale:v comparison.

To help pick appropriate values with the -qscale:v , we have run the Test Framework through some of the reference media.

| This is showing qscale values against encoding time. | | This is showing qscale values against file size. | | This is showing qscale values against VMAF harmonic mean |