Re: [FFmpeg-devel] [PATCH v2] fftools/ffmpeg_mux: fix reporting muxer EOF as error

[Anton Khirnov <anton@khirnov.net>]

Quoting Marton Balint (2023-04-23 12:05:51)
> 
> 
> On Sun, 23 Apr 2023, Anton Khirnov wrote:
> 
> > Quoting Marton Balint (2023-04-23 11:42:48)
> >> On Sun, 23 Apr 2023, Anton Khirnov wrote:
> >>> Quoting Marton Balint (2023-04-23 11:12:38)
> >>>> This seems like yet another clash of AVERROR_EOF error codes coming from
> >>>> different places with different semantics. For
> >>>> av_interleaved_write_frame(), AVERROR_EOF is an error condition, so
> >>>> file encoding should fail,
> >>>
> >>> Why should it fail? I'd think a muxer returning EOF is the way to signal
> >>> non-error muxer-side termination.
> >>
> >> That would be an API change. AVERROR_EOF is not special in any way from
> >> other error codes for av_interleaved_write_frame. A muxer cannot signal
> >> non-error muxer side termination with existing API.
> >
> > All error codes (should) have a specific meaning. I cannot think of a
> > good reason for a muxer to return AVERROR_EOF to signal an error.
> > Can you?
> 
> Previously, we expeced users to treat any negative error code as error for 
> av_interleaved_write_frame().

I don't think we expect the users to do anything in particular in
responce to av_interleaved_write_frame() return codes. The doxy says
that it returns a negative error code on error, but the caller can
freely decide what to do with that information - this includes ignoring
it.

> This is what is documented. ffmpeg.c followed this approach. Don't you
> see the slightest problem if we suddenly change this?

Seems to me you're mixing ffmpeg CLI and lavf behavior. My claim is
entirely from the point of view of the CLI, and is this: if the muxer
returns AVERROR_EOF, then it should be treated as normal termination.
This is similar to how other components behave - e.g. a (bitstream)
filter can at any time decide to return EOF to its downstream,
terminating a stream even though more input is available.

You could argue that muxers should never return AVERROR_EOF and any
muxer that currently does so is buggy, but that is still compatible with
the above.

-- 
Anton Khirnov
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