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

[Gyan]

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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>>>>> ffmpeg-devel at ffmpeg.org
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>>>>>
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>>>>> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
>>>>
>>>> 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.

Gyan