[Ffmpeg-devel] Re: [PATCH] Configure selectable video grab format

Michel Bardiaux mbardiaux
Wed Jan 31 18:27:49 CET 2007

Ramiro Polla wrote:
> Michel Bardiaux wrote:
>> Ramiro Polla wrote:
>>> Ramiro Polla wrote:
>>>> Michel Bardiaux wrote:
>>>>> M?ns Rullg?rd wrote:
>>>>> [snip]
>>>>>> That said, I don't like the design of the grabbing code at all.  
>>>>>> IMHO it would
>>>>>> be much cleaner to simply run ffmpeg -f v4l2 -i /dev/video0 or 
>>>>>> whatever,
>>>>>> dropping the whole concept of a default grabbing device used if no 
>>>>>> input is
>>>>>> specified.
>>>>> FWIW I agree.
>>>> Me too =).
>>>> The code for using a default grabbing device is really buggy (the 
>>>> grabbing interfaces depend on what has been set for output).
>>> It seems this would be just removing a bunch of redundant code (like 
>>> Michael said), and making few adaptations to the existing -i code.
>>> One problem with -i <grab device> is when you want to use the default 
>>> grab device. This could be accomplished by (some suggestions):
>>> a) using the '-' character
>> Please dont, '-' generally means stdin. AAMOF ffmpeg -i - < 
>> /dev/video0 *should* work as expected.
> Generally as in POSIX programs, or FFmpeg? (Sorry to ask. I searched a 
> little, but it's quite hard to google for "-")
>>> b) making -grab mean -i <default device>.
>> Why do you insist on having a default grab device?
> First I wanted to set the default grab *format* (as is what currently 
> happens in FFmpeg). Now I'm talking about default grab *device*.
> It would be nice to have default devices since most grab interfaces have 
> a widely used device (like /dev/bktr0, /dev/tuner0, /dev/video0...)

Widely, yes, universal, no. This would be bad for packagers, since 
whatever default device they select, might well not exist on the target 
system. Pick bktr and ship to a system with a v4l device, or the reverse.

> And for the VFW grab interface I'm writing, the devices are set by a 
> number (0-9), 0 meaning default.

Its the *system* default, no? Then under Windows, if -i 0, you should 
look up in the registry which device has been given as default.

Which suggests: "-i default" as trap value for all platforms, and look 
up in ~/.ffmpegrc for the designated default device.

> Ramiro Polla

Michel Bardiaux
R&D Director
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