[FFmpeg-devel] [PATCH] avfilter: add metadata filters

[Paul B Mahol]

On 2/10/16, Tobias Rapp <t.rapp at noa-archive.com> wrote:
> On 10.02.2016 10:59, Paul B Mahol wrote:
>> On 2/10/16, Tobias Rapp <t.rapp at noa-archive.com> wrote:
>>> On 10.02.2016 10:01, Paul B Mahol wrote:
>>>> On 2/10/16, Tobias Rapp <t.rapp at noa-archive.com> wrote:
>>>>> On 06.02.2016 23:30, Paul B Mahol wrote:
>>>>>> On 2/6/16, Paul B Mahol <onemda at gmail.com> wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> patch attached.
>>>>>>>
>>>>>>
>>>>>> Improved version attached.
>>>>>>
>>>>>> [...]
>>>>>> +
>>>>>> +static int string(const char *value1, const char *value2, size_t
>>>>>> length)
>>>>>> +{
>>>>>> +    return !strncmp(value1, value2, length);
>>>>>> +}
>>>>>
>>>>> If I understand correctly this function is used to compare if the start
>>>>> of value2 matches value1. Maybe this function should be called
>>>>> "starts_with" (also in the "function" option enum)?
>>>>>
>>>>>> +
>>>>>> +static int equal(const char *value1, const char *value2, size_t
>>>>>> length)
>>>>>> +{
>>>>>> +    float f1, f2;
>>>>>> +
>>>>>> +    if (sscanf(value1, "%f", &f1) + sscanf(value2, "%f", &f2) != 2)
>>>>>> +        return 0;
>>>>>> +
>>>>>> +    return f1 != f2;
>>>>>> +}
>>>>>> +
>>>>>> +static int less(const char *value1, const char *value2, size_t
>>>>>> length)
>>>>>> +{
>>>>>> +    float f1, f2;
>>>>>> +
>>>>>> +    if (sscanf(value1, "%f", &f1) + sscanf(value2, "%f", &f2) != 2)
>>>>>> +        return 0;
>>>>>> +
>>>>>> +    return f1 > f2;
>>>>>> +}
>>>>>> +
>>>>>> +static int greater(const char *value1, const char *value2, size_t
>>>>>> length)
>>>>>> +{
>>>>>> +    float f1, f2;
>>>>>> +
>>>>>> +    if (sscanf(value1, "%f", &f1) + sscanf(value2, "%f", &f2) != 2)
>>>>>> +        return 0;
>>>>>> +
>>>>>> +    return f1 < f2;
>>>>>> +}
>>>>>> +
>>>>>> [...]
>>>>>
>>>>> I think it would be better to not compare float values directly with
>>>>> "==", "<" or ">". Instead use some code like "fabsf(f1 - f2) <=
>>>>> epsilon".
>>>>>
>>>>> BTW: Is the return value of "equal", "less" and "greater" inverse on
>>>>> purpose?
>>>>
>>>> Not for equal, but for other it is.
>>>
>>> OK, now I got it that the argument order is flipped but matches the
>>> documentation. In that case it is a bit counter-intuitive that one has
>>> to do something like
>>>
>>> mode=print:key=mykey:value=1.0:function=less
>>>
>>> to print all metadata values of "mykey" which are *bigger* than 1.0.
>>>
>>
>> Nope, this works fine here. It prints values less than 1.0
>
> Then I have problems understanding the documentation text of "less" and
> "greater".

Ah, the problem was in documenation and code, hopefully it should be clear now.