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

[Marton Balint <cus@passwd.hu>]

On Sun, 23 Apr 2023, Anton Khirnov wrote:

> Quoting Marton Balint (2023-04-23 20:15:13)
>>
>>
>> On Sun, 23 Apr 2023, Anton Khirnov wrote:
>>
>>> 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.
>>
>> I don't understand. A good program propagates back error conditions to the
>> user, and not hides them silently.
>
> I do not think blanket claims such as this are a good idea. What is or
> is not considered "an error condition" depends on the context.
>
> As I said before - I don't see why a muxer should ever return
> AVERROR_EOF to signal a legitimate muxing error.

The real risk is that they unintentionally do that, when the error code is 
coming from some underlying operation for example.

So previsouly a muxer could return any error code to signal error 
condition and reasonably assume that ffmpeg.c will report it back to the 
user as an error.

The change in ffmpeg.c "forces" muxers to check if they ever get 
AVERROR_EOF for some real error condition and map them to 
e.g. AVERROR(EIO). And that is an API change.

Regards,
Marton
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