[FFmpeg-devel] GSoC 2016 own ideas

[wm4]

On Thu, 18 Feb 2016 18:27:45 +0100
Gerion Entrup <gerion.entrup.ffdev at flump.de> wrote:

> Good day,
> 
> I'm a master student and long term FFmpeg-user. I want to participate in the GSoC 2016 for FFmpeg. The reason, I write this, is that I want to suggest some own ideas. It could be, that some of the mentioned things are wrong (because FFmpeg could do this already or it it much more difficult than I think). Please correct me if so.
> I'm excited to hear, what do you think about this ideas, if you think, they are suitable for GSoC and if you maybe are willing to mentor some of this.
> 
> 1. *disc support
> 
> What current FFmpeg could do:
> - Bluray support through protocol support with prefix "bluray:" and libbluray. The implemention is some kind of limited. There is missing chapter support. The "main movie" selection is simply the longest one. Menus are not supported. Afaik no metadata are transfered.
> - CD support through libavdevice and libcdio. Last time I tried it, it only works under some strange circumstances (I have to set the parameter "-ss 0"). I don't know if it is fixed right now. It recognizes a CD as one track with multiple chapters. Afaik CD-Text is not supported.
> - No DVD support at all. I saw, that Stefano ones write a patch [1] (protocol and libdvdnav based), which seems to work in principal, but was probably not ready to merge.
> 
> Goal:
> - Implement an uniform solution for *disc support, that also support metadata.
> - Maybe (?): Add some kind of Menu Support, FFmpeg is not made for this atm, I think. Not sure how difficult it is.
> - Maybe (?): Try to change something on libdvdnav/libdvdread to make it more consistent (to libbluray ?). Similar idea from Flameeyes [2].

Hm, I'm not sure if that's even possible in a reasonable way. Full
DVD/Bluray support requires menus, which are hard to get right, and
which would require non-trivial interactions between applications and
libavformat.

Improving support for merely transcoding a DVD to a file might be not
so hard and potentially a good idea, though.

> Qualification task:
> - Maybe (?): Add chapter support for the current Bluray implementation (get the chapters out of libbluray is fairly simple, I'm not sure how difficult it is to get them into the stream).

This sounds like a hard design issue: currently bluray is implemented
as avio protocol, which can not pass things like chapters to the higher
level (demuxer). This would require coming up with a mechanism for
transferring this metadata, which sounds hard. Just reading the bluray
chapters should indeed be simple.

> Comments:
> - I would try to orientate on VLC, mplayer and mpv implementation.
> - libdvdread/nav seem to do much less than libbluray, so the main work would be the dvd support, I guess.
> - All kinds of discs normally contains more than one track. My idea for a solution would be, that ffmpeg recognize the disc as multiinput and choose the mainmovie as default.
> 
> 
> 2. treelike metadata
> 
> What current FFmpeg could do:
> - Metadata is always an AVDictionary (string based afaik).
> - Some metadata systems like the one of Matroska use a treelike structure (xml in mkv), so you can specify the charatername given an actor or define more than on actor, see example at the end of the mail.
> 
> Goal:
> Rewrite the FFmpeg metadata system, to support extended tags. In Detail:
> - Support for more than one value per key.
> - Support for more key/value pairs as value.
> 
> Qualification task:
> No idea.
> 
> Comments:
> Not sure, if this task is GSoC suitable.
> 

Includes API design, which is better avoided for a gsoc. I'm also not
sure if we really need such metadata, but I guess this is debatable.

> 
> 3. Vector graphic support
> 
> What current FFmpeg could do:
> - No support at all, afaik.
> 
> Goal:
> - Extend FFmpeg to support vector graphics (without converting to pixel graphics).
> - Write an SVG decoder for this.
> - Write an vector to pixel image converter/filter.
> 

That sounds not only very hard, but also very out of scope for ffmpeg.
The problem with SVG is that nothing seems to support it correctly and
entirely, so it's a good way to get hurt.

> Qualification task:
> No idea.
> 
> Comments:
> I think, this could be a very hard task. Could you comment, whether you find this suitable? I have no experience with SVG. Maybe it could be based on cairo.
> 
> 
> 4. Usable analyse filter output for programs
> Not sure, if this is a real problem at all. Not sure if this is suitable for GSoC at all.
> 
> What current FFmpeg could do:
> - Receive (multiple) streams in filter and write back other streams.
> - The problem I see here, is that the output of analyse filters is hard to process (needs some kind of subprocess and extended usage of grep/sed).
>     Examples: All filters that analyse some thing and then "print" it to stdout, like cropdetect, volumedetect, blackframe, .... Some (not implemented filter) like tonality, bpm detection, waveform analysis, ...
> 
> Goal:
> - Rewrite the filtersystem, so that some function "receive_output" exists, that could be called from the external API or another filter to get non multimedia data as the filter output, like an String for tonality, or an index array for the wavform, etc.
> 

I'm not sure if I'm following. Currently, filters like cropdetect
pass the metadata via AVFrame (as separate field besides audio/video
data), and other filters (or the API user) can read it.

> Comments:
> - Has the side effect, that a following filter in the chain could use the output to do some other stuff.
> - Not sure, how hard (and wanted) this is.
> 
> 
> 
> Other ideas, but imho not suitable for GSoC:
> - Jack output support (too simple for GSoC)
> - Python bindings

Bindings for what?

> - merge of ffmpeg and ffplay (call ffmpeg without output reacts like ffplay). Maybe this idea is fairly naive.
> 

That sounds hard, and maybe not really what we'd want anyway. (Updating
ffplay with SDL2 or something sounds more realistic.)

Nice to see a potential gsoc student showing such initiative. I hope we
can find a suitable project. Sorry if I may sound too dismissive here.

> thank you,
> Gerion
> 
> [1] https://gitorious.org/ffmpeg/sastes-ffmpeg/commit/716c1f7b2ad02a906ad1e47182492554b668f3dc?p=ffmpeg:sastes-ffmpeg.git;a=blob;f=libavformat/dvdproto.c;h=72ed431c6a47c87e30e4876587c6bb97215517cf;hb=4ed59d83a6e9fb45c3134bb67267e9b05927125c
> [2] https://blog.flameeyes.eu/2013/02/it-s-that-time-of-the-year-again
> 
> example tags from matroska:
>     ...
>     <Simple>
>       <Name>ACTOR</Name>
>       <String>Matthew McConaughey</String>
>       <TagLanguage>und</TagLanguage>
>       <DefaultLanguage>1</DefaultLanguage>
>       <Simple>
>         <Name>CHARACTER</Name>
>         <String>Jake Tyler Brigance</String>
>         <TagLanguage>und</TagLanguage>
>         <DefaultLanguage>1</DefaultLanguage>
>       </Simple>
>     </Simple>
>     <Simple>
>       <Name>ACTOR</Name>
>       <String>Sandra Bullock</String>
>       <TagLanguage>und</TagLanguage>
>       <DefaultLanguage>1</DefaultLanguage>
>       <Simple>
>         <Name>CHARACTER</Name>
>         <String>Ellen Roark</String>
>         <TagLanguage>und</TagLanguage>
>         <DefaultLanguage>1</DefaultLanguage>
>       </Simple>
>     </Simple>
>     ...
> 
> 
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