On Mon, Aug 3, 2015 at 9:30 PM, Nicolas George <geo...@nsup.org> wrote:
> Le sextidi 16 thermidor, an CCXXIII, Michael Niedermayer a écrit :
>> i also found this comment in a patch in my inbox:
>>
>> + /* When using Standard C input functions, also check if there
>> + is anything in the buffer. After a call to such functions,
>> + the input waiting in the pipe will be copied to the buffer,
>> + and the call to PeekNamedPipe can indicate no input available.
>> + Setting stdin to unbuffered was not enough, IIRC */
>> + if (stdin->_cnt > 0)
>> + {
>> + char ch;
>> + //Read it
>> + read(0, &ch, 1);
>> + return ch;
>> + }
>>
>> This seems to explain what the code was intended to do
>
> That was my guess.
>
> This is ugly, and should be removed anyways. It is not possible to mix stdio
> and low-level reading like that, period.
>
> Fortunately, ffmpeg.c only uses stdin at one single place, a few lines below
> the corresponding code:
>
> }else
> if(scanf("%d", &debug)!=1)
> fprintf(stderr,"error parsing debug value\n");
>
> It needs to be changed to read a line with the low-level function
> (read_key()), exactly like 40 above for the 'c' case. I can not brew a patch
> right now, sorry.
>
> I suspect this would not work:
>
> printf 'd42\nC ... fontfile ...\n' | ffmpeg ...
>
> because the C will end up in the stdio buffer.
>
>
Good catch. This command doesn't work with or without the hunk this
patch removes however.
A simpler command without drawtext would be:
printf 'd0\n?' | ffmpeg -i ...
If you see help output, it works. Using another command instead of d0
works fine, like a C command followed by a \n?
It also doesn't work on Linux, so thats a more fundamental problem.
Since this fixes a build failure, unless we can find a use-case where
this hunk actually does make a difference, I would still rather remove
it.
If it causes any regression in the future, which we didn't think of
now, I'll be here to work on a fix.
- Hendrik
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