Re: Presets and profiles

[Stefan Kost <ensonic hora-obscura de>]

Daniel G. Taylor schrieb:
> On Mon, 2009-05-04 at 11:30 +0100, Christian Fredrik Kalager Schaller
> wrote:
>   
>> Hi everyone,
>>     
>
> Hey,
>
>   
>> Daniel G. Taylor and myself have been working on defining a
>> specification for how we want to handle things like profiles and presets
>> for transcoding to various devices. The initial usecase is for devices
>> you do not have attached to your computer, but we love to get feedback
>> on how we might want to adjust the current specifications to work better
>> for that usecase too.
>>
>> There are two documents so far, the first one discussing element level
>> presets using the GStreamer preset interface:
>> http://gstreamer.freedesktop.org/wiki/PresetDesign
>>
>> The second is a device level description of the Device in XML:
>> http://gstreamer.freedesktop.org/wiki/DeviceProfile
>>
>> Both documents will probably see quite some changes still, so please
>> feel free to give feedback and suggestions.
>>
>> We do hope that this stuff ends up being used beyond Arista and
>> Transmageddon once it matures a bit, for instance Sound Juicer could use
>> the Audio information in here for example.
>>     
>
> Just thought I'd mention that there are some great comments on the wiki
> left by Mike Smith.
>
> I agree that the use of two different formats for the files seems
> unnecessary - I believe it's because of how the presets for GStreamer
> are currently setup, right? I'd prefer one format and don't really care
> which one, though obviously currently Arista is using XML (and the
> format is not stable yet).
>
> In case anyone else misunderstands the passes section in both Arista and
> the DeviceProfile wiki page: it's merely a way to define what should be
> done for each pass of an encode. In the example we have only one pass
> that is based on constant quality, but you could easily see where you'd
> want two pass bitrate-constrained encodes (see Nokia N810 for example),
> and the passes section allows you to define multiple passes to
> accomplish this. As a working example, in Arista trunk it currently runs
> through each pass one after another to produce the final file. In each
> pass element you put the options for that pass (or in the DeviceProfiles
> case the profiles that all elements must provide given the caps like
> video/x-h264, which are defined on the PresetDesign page).
>
> I also agree that the syntax is not well defined in the wiki for certain
> elements. Here is how it works in Arista:
>
> Each element that gives a constraint is allowed to be either a single
> value (e.g. <param>10</param>) or an inclusive range (e.g. <param>10,
> 30</param>). Internally the single parameter is turned into a range of
> e.g. [10, 10] and all calculations in while setting up the transcoder
> are done using those ranges (scaling, resampling, etc). I agree that one
> shortcoming is not allowing a list of discrete values or allowing
> something like e.g. <param>320, 720 % 16</param> to say that the value
> can be between 320 and 720 but must be a multiple of 16. I'm working on
> this for Arista and will probably be updating the GStreamer wiki with
> more info soon as well.
>
> Perhaps it is more useful to direct people to post here rather than the
> wiki? Having conversations on a wiki has never really been very
> successful for me.
>
> Take care,
>   

Okay here are my comments (now removed from the wiki):
Totally agree with Mike regarding the devce capabilities. What about even:
video/x-h264, width=[320, 640], height=[240, 480], framerate=(fraction)1/30
you could e.g. reuse the capssrting and put it on a capsfilter as it is
(except the media-type).

Also agree that xml feature are slight overkill here. The purpose of the
device profile is to describe the suggested format and limitation for a
certain device.

On IRC I was suggesting to also take os-versions into account, so that
we end up with profiles like this:
PC.WindowsXP      // use avi with mpeg4 and mp3
PC.WindowsVista   // use asf with wmv and wma
PC.Linux          // use ogg with theora and vorbis
N8x0.Maemo4       // use avi with mpeg4 and mp3
N8x0.Maemo5       // use mp4 with h264 and aac

It could be consided to have a unversioned fallback (N8x0 that even
could be a symlink incase someone does not know the version).

Stefan

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