ProRes
There are four Prores encoders, Prores, Prores_ks, Prores_aw and prores_videotoolbox, which is a hardware based OSX M1 encoder/decoder (ffmpeg version 5 or higher).
From https://trac.ffmpeg.org/wiki/Encode/VFX the recommendation is to use Prores_ks with -profile:v 3 and the qscale of 11 unless you are on OSX where we would recommend using prores_videotoolbox.
The two encoders we are reviewing are:
- Prores_ks
- videotoolbox_prores - only available on osx.
Prores_ks
While prores does support up to 12 bits of resolution, prores_ks can only encode to 10-bits. It is able to decode to > 10 bits (see https://github.com/ColorlabMD/Prores-BitDepth )
Supported pixel formats: yuv422p10le yuv444p10le yuva444p10le
Example encode would look like:
ffmpeg -r 24 -start_number 100 -i inputfile.%04d.png \
-pix_fmt yuv422p10le -vf "scale=in_color_matrix=bt709:out_color_matrix=bt709" \
-frames:v 100 -c:v prores_ks -profile:v 3 -vendor apl0 -qscale:v: 10 \
-color_range tv -colorspace bt709 -color_primaries bt709 -color_trc iec61966-2-1 \
-y outputfile.mov
Options that can be used include:
| -profile:v 4444xq | Which prores encoding profile to use, see below |
| -qscale:v 10 | 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. |
| -alpha_bits 16 | Allows you to specify how many bits to use for the alpha channel (default 16) |
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 recognized, 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 recognized 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
Prores_ks profile
Profile values can be one of:
| Profile | Number | Chroma | Data Rate HD @ 29.97 | Description |
|---|---|---|---|---|
| proxy | 0 | 4:2:2 | 45Mbps | Proxy |
| lt | 1 | 4:2:2 | 102Mbps | Light |
| standard | 2 | 4:2:2 | 147Mbps | Standard |
| hq | 3 | 4:2:2 | 220Mbps | High Quality 10-bit |
| 4444 | 4 | 4:4:4:4 | 300Mbps | High quality mastering format, can support both RGB and Y’CrCb. Also supports a 16-bit mathematically lossless alpha. |
| 4444xq | 5 | 4:4:4:4 | 500MBps | High quality mastering format, supports up to 12 bit, and 16-bit alpha. ffmpeg will only generate up to 10-bit. |
See https://support.apple.com/en-us/HT202410
To compare them:
 This is showing profile values against encoding time. |  This is showing profile values against file size. |
 This is showing profile values against VMAF harmonic mean (quality) |
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 (quality) |
videotoolbox_prores
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 \
-pix_fmt yuv422p10le \
-vf "scale=in_color_matrix=bt709:out_color_matrix=bt709" \
-vframes 100 -c:v prores_videotoolbox -profile:v 3 \
-color_range tv -colorspace bt709 -color_primaries bt709 -color_trc bt709 outputfile.mov
NOTE, it does not appear to allow -color_trc iec61966-2-1 (sRGB) – so this needs more testing.
Prores_videotoolbox profile
Similar to prores_ks, with the exception of xq. Profile values can be one of:
| Profile | Number | Chroma | Data Rate HD @ 29.97 | Description |
|---|---|---|---|---|
| proxy | 0 | 4:2:2 | 45Mbps | Proxy |
| lt | 1 | 4:2:2 | 102Mbps | Light |
| standard | 2 | 4:2:2 | 147Mbps | Standard |
| hq | 3 | 4:2:2 | 220Mbps | High Quality 10-bit |
| 4444 | 4 | 4:4:4:4 | 300Mbps | High quality mastering format, can support both RGB and Y’CrCb. Also supports a 16-bit mathematically lossless alpha. |
| xq | 5 | 4:4:4:4 | 500MBps | High quality mastering format, supports up to 12 bit, and 16-bit alpha. ffmpeg will only generate up to 10-bit. |