[FFmpeg-user] ffmpeg output list question

[Carl Eugen Hoyos]

Am So., 15. Dez. 2019 um 16:50 Uhr schrieb Mark Filipak
<markfilipak.windows+ffmpeg at gmail.com>:
>
> I run this command:
> ffmpeg -ss 30.0 -i %1 -hide_banner -filter:v idet -frames:v 900 -an -f
> rawvideo -y NUL
> to gather data on multimedia source files (passed in via %1).

When asking questions on this mailing list, please do not use
-hide_banner (unless you want to report an issue with this
option).

> I've run it against a wide mix -- close to a hundred -- sources:
> - 24 FPS,
> - 25 FPS,
> - soft telecined,
> - hard telecined, and
> - NTSC with embedded hard telecined (e.g., "Making of" documentaries).
> I've included a typical output (with added line #s) at the bottom of
> this message.
>
> Question: Is the output listing documented anywhere?
> Of particular interest are:
> - the meaning of "tbr" (line 04),
> - the meaning of "tbc" (line 04),

Different time bases, tbn is the container, tbc is codec iirc.

> - the meaning of "dup" (line 18),

This is a message from the ffmpeg executable to tell you how many
frames were duplicated to get cfr output.

> - why 'dup'+'drop'+'Neither'+'Top'+'Bottom' (lines 18 & 20) always
> equals 901, and

dup is not related to neither top and bottom
(although the sum is related to your 900 request)

You can use -vsync 0 for your use case, it will avoid the duplicate
frames.

> - why 'Neither'+'Top'+'Bottom' (line 20) totals 830 instead of 1660.

I wrote originally:
Because there are less input frames than output frames, this is
related to the fact that your input are mpeg streams.

But the answer is more likely:
FFmpeg (and digital transcoders in general) doesn't know about fields,
it can only work with frames. (This is also related to the specifications
of sane video codecs.)

Carl Eugen