[FFmpeg-user] Create slideshow with ffmpeg from still images

[thljcl]

Yes, I’m aware of the fact that ffmpeg can be used to concatenate videos
Physical concatenation protocol. 
Allow to read and seek from many resource in sequence as if they were a
unique resource. 
A URL accepted by this protocol has the syntax: 
 	concat:URL1|URL2|...|URLN

where URL1, URL2, ..., URLN are the urls of the resource to be concatenated,
each one possibly specifying a distinct protocol. 
For example to read a sequence of files ‘split1.mpeg’, ‘split2.mpeg’,
‘split3.mpeg’ with ffplay use the command: 
 	ffplay concat:split1.mpeg\|split2.mpeg\|split3.mpeg

Note that you may need to escape the character "|" which is special for many
shells. 
But I can make my own choice to use the tools I prefer, can I not?
With regards to reporting bugs to ffmpeg developers, I do not in this case
discover a bug, so to speak. If it sounds like a bug to you; suite yourself
to report it. I’m sure that you can test it to find the bugs yourself.
Bear in mind, frame rate conversion from one constant frame rate to another
always involves adding or dropping frames. As users, we might not know the
algorithms behind the video filter “fps”; that’s why I specifically perform
a number of tests to find out how it decides which frames it adds or drops.
I would consider the frame rate conversion is “flawed” if such a condition
is true: the conversion process is not reversible. Well, allows me to
elaborate further.
If the original source is of the frame rate of lower frame rate, when its
frame rate is to be converted to higher frame rate, it would involve the
duplication of frames; of course the question of which frames would be
duplicated depends on the algorithms designed by the developers. When the
video of higher frame rate with duplicated frames undergoes frame rate
conversion so that the output would have the original frame rates, only
duplicated frames would be dropped. Even though the length of the videos
would change due to frame rate conversion, repeated conversion from one to
another and vice versa would not change the video length for a specific
frame rate. Of course, if the source of higher frame rate with no duplicated
frames undergoes frame rate conversion to achieve lower frame rate, such a
process is irreversible, as expected.
Based on my own tests, ffmpeg passes my expectation of how frame rate
conversion should be handled. That’s why I do not discover a bug. However,
if you find bugs from my experience, feel free to report it and publish it.
I have to say that the basic idea behind the duplication of frames to create
a slideshow involves a feature in ffmpeg which is frame rate conversion. In
effect, we use frame rate conversion algorithms to cause ffmpeg to duplicate
frames for us, instead of manually copying frames to create a slideshow.
I’m not absolutely sure that my way of creating a slideshow is particularly
good or superior, that’s why I did not attempt to edit the ffmpeg wiki.
No, it’s not meant for propagating my views of world. In fact, similar
questions have been asked before at http://bit.ly/13rjKL3 and
http://bit.ly/1cgluyH. But while I believe that my experience may be helpful
to somebody, it does not directly answer their questions. Speaking of
questions the users may ask, it’s indeed a question. It is a question I
would ask myself as well as other possibly much more skillful users of
ffmpeg. I gave my “workaround”. But in no way I suggested that somehow I
gave a perfect answer. If I sound like such, I apologize in advance.
Presumably, somebody else may have better answers for what I saw or what I
want to achieve. Possibly, my understanding of how ffmpeg works is
misguided.
That's why I specifically try to extract all the original non-duplicated
frames from the created slideshow, which is successful, I have to say.



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