[FFmpeg-devel] 答复: 答复: [PATCH]Filter: Add snapshot filter. It is enable to save snapshot.

Tobias Rapp t.rapp at noa-archive.com
Mon May 30 12:18:15 CEST 2016

On 28.05.2016 07:31, kl222 wrote:
> On 27.05.2016 13:49, Nicolas George wrote: 
>> Can you explain your use case for this filter?
>> I ask because I am very uncomfortable with filters that perform direct output
>> instead of producing frames for the rest of the graph. They need to duplicate
>> the encoding and muxing code, usually with fewer options and features, and
>> that duplicated code becomes itself a maintenance burden in case of API
>> changes and such.
>> IMHO, a better solution would be some kind of "interactive select" (or just an
>> option of plain select) filter, and encode its output as image2.
> I want to implement to the snapshot function whenever push stream, 
> and set the file name of snapshot picture. 
> this function can snapshot pictures before, between or after the other filters.
> Because I want to change the file in filter, so duplicate the encoding and muxing code
> can not be avoided. 
> OK, add it to "select" filter and a single filter patch. Chosen by you. see annex.

The way you added it to the select filter it still uses own muxing code and doesn't 
allow to take full advantage of output format options.

To give an idea what I had in mind when suggesting the select filter: The following 
command uses current FFmpeg code to generate snapshot files of the first two video 

ffmpeg -i input-file.avi -f image2 -q 5 -filter:v "select=lt(selected_n\,2)" -y snapshot-%03d.jpg

Now if the select filter code would be improved to allow updating the evaluated 
expression at run-time, sending filter commands like

expr lt(selected_n,2)  // save two snapshot files
expr lt(selected_n,3)  // add another snapshot file
expr lt(selected_n,4)  // add another snapshot file

could be used to trigger saving snapshot files on demand.


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