[FFmpeg-trac] #6525(ffmpeg:new): Still image file format codecs are tricky to filter out of -codecs output
FFmpeg
trac at avcodec.org
Sat Jul 15 02:06:46 EEST 2017
#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.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/6525>
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