[FFmpeg-trac] #6525(ffmpeg:new): Still image file format codecs are tricky to filter out of -codecs output

[FFmpeg]

#6525: Still image file format codecs are tricky to filter out of -codecs output
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             Reporter:  tangent      |                     Type:
               Status:  new          |  enhancement
            Component:  ffmpeg       |                 Priority:  normal
             Keywords:  codecs,      |                  Version:  3.2.4
  help, output                       |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 I am interested in constructing a short command that reliably filters
 `ffmpeg -codecs` output to show only the list of lossless video encoders.
 So far, I have come up with this:

 {{{
 $ ffmpeg -codecs 2> /dev/null | grep '^..EV..S ' | grep -Ev 'image|bitmap'
 }}}

 The second `grep` command filters out a bunch of codecs I'm not interested
 in like `bmp` and `pcx` because they are not "video" codecs in the way I
 understand the term.

 There is something of a gray area here, which I will deal with below.

 I propose that these encoders have their `V` tag  in the `DEVILS` scheme
 replaced by either `I` or `M`:

 *   `I` means an "image" codec, and implies that you can only encode one
 frame at a time with this codec, and that each frame will have a separate
 image header. I believe `bmp` is in this class, for example. To make a
 single-file movie with this encoder, you must put it into a container like
 AVI, MKV, or MPEG-TS.

     I propose that a still image file format like `jpeg-ls` keeps its `V`
 tag because it is often used within an A/V container format: `avi` +
 `jpeg-ls` = Lossless MJPEG, so `jpeg-ls` is a "video" codec to me. I'm not
 aware of anyone using `avi` + `bmp`, by contrast.

     A thought experiment you can use to decide this issue is to ask
 whether you are likely to find this encoder used as the argument to an
 `-f` flag or a `-c:v` flag. We expect `bmp` to be used with `-f` for a
 "pile of frames" output, but `jpeg-ls` to be used with `-c:v` and some
 container format with `-f` to produce a single-file movie.

 *   `M` means a format like `gif` or `apng` that allows multiple frames
 with timing information per file, so that you don't need the container if
 you don't need associated audio or other streams.

 If that idea is rejected, at least give some other way to reliably filter
 these codecs out of the `ffmpeg -codecs` output. I'd like to see you
 settle on either `bitmap` or `image` and apply that term uniformly to all
 of the still image file formats I'm talking about here.

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Ticket URL: <https://trac.ffmpeg.org/ticket/6525>
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