[FFmpeg-devel] Read this if you are porting filters from MPlayer

Daniel G. Taylor dan
Mon Dec 6 23:17:58 CET 2010

On 12/02/2010 09:46 PM, Michael Niedermayer wrote:
> its embarrassing but i was unware of them being students from code in.
> if them being high scool students being considered i agree with you that my
> comment was way too harsh, i was writing this in the belive that they where
> older and experienced developers

A few comments as someone who successfully ported the unsharp filter and 
attempted to modify some other filters:

  1. Just because you are older or more experienced does not mean that
     you know how FFmpeg works, and not knowing some of the stricter
     (and fairly strange compared to other projects) policies shouldn't
     necessarily result in lashings in front of the community.

  2. Everyone is a student until they learn the ropes, and this includes
     older and/or more experienced developers.

  3. Modifications are sadly not as simple as you've led them on to be.
     I'll use as an example here the modifications I've tried to make to
     the scale filter to prevent the following from happening:

$ ffmpeg -i foo.flv -vf scale=320:-1 -vcodec libx264 -vpre fast out.mp4
[scale @ 0xa890710] w:390 h:240 fmt:yuv420p -> w:320 h:197 fmt:yuv420p 
[libx264 @ 0xa8954c0] width or height not divisible by 2 (320x197)
Error while opening encoder for output stream #0.0 - maybe incorrect 
parameters such as bit_rate, rate, width or height

As you can see it still happens in trunk, was reported months ago, has 
several working patches to fix it, but has been going back and forth 
forever with no end in sight and feature creep like you wouldn't 
believe. I don't mean to push my issue here but I mean to illustrate 
that working with FFmpeg is frustrating, especially if you only try to 
contribute occasionally, and especially if you are only allocated a 
small amount of time at work to do so.

I'm very happy to see Jason try and bring in new blood, and very happy 
to see you both agree to take it easy on the new students. I really, 
really appreciate all the work that Jason has done to try and make x264 
and FFmpeg easier to use. I only hope this is the start of a trend to 
treat everyone that is trying to help you and your project better.

Anyway, I wish the students well and hope we get a lot of nice filters 
as a result of efforts like this.

Take care,
Daniel G. Taylor

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