[Libav-user] I'll ask in other words - how can I force input frame rate?

[Matthew Einhorn]

On Mon, Oct 10, 2011 at 3:32 AM, wl2776 <wl2776 at gmail.com> wrote:
>
> Steffen Ebersbach-2 wrote:
>>
>>> wl2776 wrote:
>>>
>>> So, it is possible to force input frame rate. How can I do it in my
>>> application?
>>>
>>
>> Hello,
>>
>> in an own application you have to do this resampling by your self. If
>> you have 2fps input and 25fps output, it means that you have to write
>> each picture from the input 12,5 times to the output. In fact this is
>> not possible, so you have to do 12 and 13 pictures for each second. The
>> code should look like this
>>
>> - read input sample
>>
>> while < 12 (13)
>>      - write to the output
>>      - wait 40ms
>>
>> .. and so on
>>
>
> Sorry for repeating quotes, one more thing, which probably is not obvious.
> You can specify "-r" switch (set frame rate) in the command line of ffmpeg
> *before* "-i" switch.
> This makes ffmpeg to consider that *incoming* frame rate is given from
> outside and it should not neither determine nor assign a default value.

You might want to look into av_set_string3() in opt.h. I don't know if
it'll help you but you can use it to set stuff like from the command
line.