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

[Paul B Mahol]

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.

>
> Another sidenote: I have seen that some filters use a common expression
> language (e.g. aeval, crop, scale). Not sure if this expression language
> supports string operators or if it is limited to numbers but in my
> opinion it would be great to re-use it here.

Added and applied. Filter is easily extendable.