image2 to support start_index and step_increment

[burek]

image2 could be improved to support 2 new parameters, namely start_index and step_increment (or similar), that would be used like this:

for encoding:

ffmpeg -i input -f image2 -start_index 14 -step_increment 3 out%04d.png

this would produce following files: out0014.png, out0017.png, out0020.png, out0023.png, ...

for decoding:

ffmpeg -f image2 -start_index 14 -step_increment 3 -i in%04d.png

this would expect following files on input: in0014.png, in0017.png, in0020.png, in0023.png, ...

[saste]

We already have a -start_number and support glob patterns.

As for -step_increment, it seems to cover a rather specific requirement which can be easily addressed with some scripting, so I prefer to avoid the avoidable complexity of its implementation.

[saste]

Closing the ticket. Please reopen if you think there is a specific use case for the -step_increment option.