[FFmpeg-devel] Libavcodec consulting

[Eran Kornblau]

> 
> Thanks for that clarification. Unfortunately the http server is a third
> party camera that broadcasts a WiFi hotspot. Therefore we don't really
> have control over the underlying server. However, what I do know is
> that the ffmpeg command I quoted previously seems to be able to
> grab a chunk of a video anywhere in the file without downloading the
> whole thing. So I assume libav must also be capable.
>
The nginx module we develop https://github.com/kaltura/nginx-vod-module 
has the capability to efficiently clip MP4 files - 
1. It downloads the index (moov atom) whether it's in the beginning of the file 
or at its end
2. It generates a new 'clipped' index for the output video
3. It determines the relevant range of the video/audio frames in the original
file, and serves it to the client

In addition, this module has the ability to work in remote mode - it can pull the 
relevant sections of the file using HTTP range requests.
So, easiest solution, assuming you can set up some server (and you don't have 
to provide a client-only solution) would be to set up such a "clipping proxy"
and have the mobile app simply download the clip from the proxy (providing 
the clipping from/to offsets)
If a server solution is not option, you can still use our code as a reference for 
the implementation.

Btw, nginx has a built-in module for clipping MP4 files - 
http://nginx.org/en/docs/http/ngx_http_mp4_module.html 
But our module has several advantages compared to built-in version, incl:
1. Support for remote (HTTP) MP4 files
2. Support for MP4 files in which the index is at the end of the file

Hope this helps

Eran