[GRASS5] Re: GRASS and configure

[Bob Covill]

Glynn,

Thanks for your help that did the trick.

Glynn Clements wrote:
>>I have mostly got the FFMPEG configure stuff working. The problem is 
>>that ffmpeg consists of 3 libraries (avcodec, avutil and avformat). The 
>>avcodec library is the one that I need and have set up for in configure. 
>>Unfortunately, depending on the system avcodec requires avutil.
> 
> 
> Let me guess; you're making the NVIZ animation feature generate video
> files directly?

Yes ... you guessed it. I have been sitting on the code for a while but 
have not properly incorporated it. I have added it as a space and time 
saving option. When creating animations with > 1000 frames you need a 
fair bit of disk space for the images. You only need a fraction of the 
space for the encoded video, and in the tests I have run it is much 
faster than rendering individual images.

> 
> If so: while I can understand that it might be more convenient, there
> are two problems.
> 
> 1. It creates yet more reasons why NVIZ may fail to compile. NVIZ is
> already the hardest part of GRASS to build due to Tcl/Tk and OpenGL
> issues, and video encoding libraries are several orders of magnitude
> more complex than either Tcl/Tk or OpenGL (and usually in a permanent
> "beta" state).
> 
> 2. The number of parameters which can control exactly how a sequence
> of images is turned into an AVI (or similar) file is immense, and
> varies from one build of ffmpeg to another. These kinds of issues are
> arguably best left to a stand-alone encoder.

Right now I have it set up to with the parameters hard coded to encode a 
simple MPEG1VIDEO. This does not have quite as many restrictions (such 
as aspect ratio, etc) as other video formats. Hopefully, if this takes 
off, user set encoding options and formats can be added.

> 
> If you are planning on adding ffmpeg support to NVIZ, please make it
> optional. Being able to compile ffmpeg shouldn't be a mandatory
> prerequisite for compiling NVIZ.
> 

I definitely agree with this. I hate getting software that will not 
compile unless I get a bunch of other required packages. The default 
will be for FFMPEG support to be off. If the user wants to encode video 
directly they will have to get and install FFMPEG and set the GRASS 
configure option. NVIZ will function normally without ffmpeg (just no 
direct video encoding).

Thanks again for your help.

--
Bob

> 
>>My question is; is it possible to spcify two libraries in the 
>>LOC_CHECK_LIBS() so that the output (FFMPEGLIB in my case) is defined as 
>>two libraries (i.e -lavcodec and -lavutil)? Or do I have to create 
>>seperate variables for each library?
> 
> 
> You can specify that certain additional switches may be required by
> passing them as the 9th and subsequent arguments, e.g.
> 
> LOC_CHECK_LIBS(avcodec,avcodec_init,AVcodec,$AVLIBPATH,AVCODECLIB,,,,-lavutil)
> 
> This will try to find avcodec_init first with just:
> 
> 	... $AVLIBPATH -lavcodec
> 
> then with
> 
> 	... $AVLIBPATH -lavcodec -lavutil
> 
> If the first test passes, AVCODECLIB will be set to "-lavcodec"; if
> the first fails but the second passes, it will be set to
> "-lavcodec -lavutil".
>