Why does ffprobe report color space as unknown?

Question

If the caja file properties report YUV for color space, why does ffprobe report color space as unknown ?

The video in question was obtained from Astronomy Picture of the Day (APOD) Spinning Moon.

Here is the snapshot from caja:

ffprobe reports as follows:

# ffprobe -v error -show_streams "${file}"
FILE: VIDEO__MOON__SpinningMoon.mp4
[STREAM]
index=0
codec_name=h264
codec_long_name=H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
profile=Main
codec_type=video
codec_time_base=1/60
codec_tag_string=[27][0][0][0]
codec_tag=0x001b
width=640
height=800
coded_width=640
coded_height=800
has_b_frames=2
sample_aspect_ratio=1:1
display_aspect_ratio=4:5
pix_fmt=yuv420p     <<<===
level=32
color_range=unknown     <<<===
color_space=unknown     <<<===
color_transfer=unknown     <<<===
color_primaries=unknown     <<<===
chroma_location=left
field_order=progressive
timecode=N/A
refs=1
is_avc=false
nal_length_size=0
id=0x1e1
r_frame_rate=30/1
avg_frame_rate=30/1
time_base=1/90000
start_pts=192410
start_time=2.137889
duration_ts=1959000
duration=21.766667
bit_rate=N/A
max_bit_rate=N/A
bits_per_raw_sample=8
nb_frames=N/A
nb_read_frames=N/A
nb_read_packets=N/A
...{snip - DISPOSITION:*}...
[/STREAM]

But when I play the video in VLC, it reports CODECs as follows:

I must say that when I start the playing in VLC, the moon image is initally presented (for a fraction of a second) as an elipse going full width of the screen, but then it blanks out and continues with "proper" proportions (i.e. near circle), and when I tell VLC to go on repeat loop, you don't see that initial "deformation" (as if it was able to figure something out and remember that as a setting, during ongoing playback).

QUESTION: Is the reporting of "unknown" for the color space parameters a bug with ffprobe/ffmpeg, even though it has recognized the pixel format at "yuv420p"? Is that an oversight in coding?

My environment:

Ubuntu MATE 20.04 LTS

ffprobe version 4.2.7-0ubuntu0.1 Copyright (c) 2007-2022 the FFmpeg developers
built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)

Answer 1

caja is using mediainfo and mediainfo has some misleading labels.

What mediainfo is describing as Color space is more accurately a color model. What ffprobe displays is the pixel format (pix_fmt) which is the specific combination of color model, chroma subsampling, bit depth and component interleaving that the decoder will produce.

A Color space is a mathematical organization of reproducible colors. Two videos may both have YUV (or RGB) encoding and yet have different color spaces. If the output device doesn't know or guess the color space of the image/video, reproduced colors will be different from what is intended.