[FFmpeg-devel] [PATCH] avfilter/f_loop: do not loop if loop size is 0

[Marton Balint]

On Mon, 20 May 2019, Gyan wrote:

>
>
> On 20-05-2019 02:18 AM, Marton Balint wrote:
>>
>>
>> On Sun, 19 May 2019, Paul B Mahol wrote:
>>
>>> On 5/19/19, Marton Balint <cus at passwd.hu> wrote:
>>>>
>>>>
>>>> On Sun, 19 May 2019, Paul B Mahol wrote:
>>>>
>>>>> On 5/19/19, Marton Balint <cus at passwd.hu> wrote:
>>>>>> Fixes infinte loop with -vf loop=loop=1.
>>>>>>
>>>>>> Possible regression since ef1aadffc785b48ed62c45d954289e754f43ef46.
>>>>>>
>>>>>> Signed-off-by: Marton Balint <cus at passwd.hu>
>>>>>> ---
>>>>>>  libavfilter/f_loop.c | 2 +-
>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/libavfilter/f_loop.c b/libavfilter/f_loop.c
>>>>>> index d9d55f9837..3da753dd1e 100644
>>>>>> --- a/libavfilter/f_loop.c
>>>>>> +++ b/libavfilter/f_loop.c
>>>>>> @@ -343,7 +343,7 @@ static int activate(AVFilterContext *ctx)
>>>>>>
>>>>>>      FF_FILTER_FORWARD_STATUS_BACK(outlink, inlink);
>>>>>>
>>>>>> -    if (!s->eof && (s->nb_frames < s->size || !s->loop)) {
>>>>>> +    if (!s->eof && (s->nb_frames < s->size || !s->loop || 
>>>>>> !s->size)) {
>>>>>>          ret = ff_inlink_consume_frame(inlink, &frame);
>>>>>>          if (ret < 0)
>>>>>>              return ret;
>>>>>> -- 
>>>>>> 2.16.4
>>>>>>
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>>>>>
>>>>> I think better fix is to change default and minimal allowed loop 
>>>>> size to
>>>>> 1.
>>>>> Does that sounds ok to you?
>>>>
>>>> Well, looping the whole length of the input would be more intuitive 
>>>> to me
>>>> as the default.
>>>
>>> That would require infinite memory.
>>
>> So as the reverse filter. As long as it is properly documented that 
>> the looped stuff is kept in memory so the user should not use this for 
>> long clips, then I think it is fine.
>
> I disagree. Yes, for loop with only loop specified, it would be 
> intuitive to loop the whole stream, but relying on users to exercise due 
> diligence can't be counted upon. We're talking about a scenario where 
> the user hasn't bothered to specify the size variable because they don't 
> know or don't care or are sloppy. They won't take heed of the 
> documentation until the command fails. The defaults should be robust 
> against lax use.

Fair enough, although I never liked the idea that we make the tool less 
handy because we target unexperienced users.

Anyway, I don't have strong feelings about this, maybe my patch has the 
benefit of keeping existing behaviour (which is similar to how aloop 
works) in contrast to what paul suggested, but I don't really mind Paul's 
or Bela's solution either.

Regards,
Marton