Question on "-aspect" in the docs

[idest]

In the documentation to the ffmpeg tool, at the end of the -aspect option description there's a phrase:

If used together with -vcodec copy, it will affect the aspect ratio stored at container level, but not the aspect ratio stored in encoded frames, if it exists.

Here "stored at container level" should probably be replaced with "stored at video stream metadata level".

ffmpeg N-118724-g73f4668ef8-20250310.

[Gyan]

The change makes it less accurate and less precise.

Do you think otherwise? Why?

[idest]

Do you think otherwise? Why?

I do, the reason is this: if you change aspect ratio with a command like this:

ffmpeg -i in.mp4 -aspect 11:3 -vcodec copy out.mp4

, and then analyze the resulting video with ffprobe:

ffprobe -show_format -show_streams out.mp4

, you'll notice that the "sample_aspect_ratio" and "display_aspect_ratio" values, which are related to aspect ratio, are shown in the [STREAM] (video stream metadata) section, not in the [FORMAT] (container level) one.

[Cigaes]

Your assumption that [FORMAT] = “container level” is unfounded. [STREAM] contains information both from the container and the bitstream.

[idest]

Your assumption that [FORMAT] = “container level” is unfounded.

I think it's what ffprobe documentation says:

1. (in the "Description" section): Metadata tags stored in the container or in the streams are recognized and printed in the corresponding "FORMAT", "STREAM", "STREAM_GROUP_STREAM" or "PROGRAM_STREAM" section.
2. (in the -show_format description): All the container format information is printed within a section with name "FORMAT".
3. (in the -show_streams description): Each media stream information is printed within a dedicated section with name "STREAM".

[Cigaes]

Looks accurate.

Note that the aspect ratio is not part of what is specifically called metadata.

[Gyan]

Container information is that which is written by the muxer.

Video stream metadata i.e. metadata stored about a stream can be
1) written into a container field by the muxer
and/or
2) embedded within the coded bitstream by the encoder or a bitstream filter.

-aspect only affects (1).

[idest]

-aspect only affects (1).

Sorry if I'm being stupid now, but doesn't the phrase

"If used together with -vcodec copy, it will affect the aspect ratio stored at container level, but not the aspect ratio stored in encoded frames, if it exists" (that's from -aspect description)

imply that -aspect affects (2) if used without -vcodec copy?

[Gyan]

If encoding, -aspect affects both (1) and (2).

[MasterQuestionable]

͏    https://ffmpeg.org/ffmpeg.html#Video-Options