[FFmpeg-devel] Confusion over temporal filters.

[Marton Balint]

On Sun, 10 Sep 2017, Paul B Mahol wrote:

> On 9/10/17, Richard Ling <divetec at rling.com> wrote:
>> I'm thinking of adding a temporal filter (one that relies on context from
>> previous frames), and I've realised I'm a bit confused about how they
>> should work.
>>
>> Say I open a file with ffplay and let it play up to frame 100.  Then I open
>> the same file with another instance of ffplay and seek directly to frame
>> 100.  It seems to me that frame 100 should look the same in both cases.
>> Put another way, a specific set of filters, applied to a specific file,
>> should completely define what every frame of that file looks like.  Seeking
>> around in the file should not change that.  Is that right (in principle)?
>>
>> So, looking at some of the existing temporal filters (eg. deflicker), I
>> don't think that is what happens.  They filter based on the frames
>> previously passed to the filter, and if the user seeks over a bunch of
>> frames, the filter will see frames as consecutive that are not actually
>> consecutive in the file, so it will give a different result.  Also, looking
>> at the API, I can't see a way to get the behaviour I expect.  I can't see a
>> way for a filter to ask its inputs for a frame from a different (specific)
>> time.  Is that right?
>>
>> If my understanding is wrong, please let me know!
>>
>> If my undersanding is correct, then I guess my questions are:
>> (1) is this behaviour a known issue (or a deliberate design choice)?
>
> Both. There is no seeking in lavfi (yet).

Actually ffplay re-creates the filter chain after every seek 
flushing any state of the filters, therefore non-consecuitve frames are 
not passed to the filters.

Regards,
Marton