[FFmpeg-soc] [soc] libavsequencer [PATCH 01/08] Music module public API header file.

[Sebastian Vater]

Vitor Sessak a écrit :
> On 07/11/2010 12:58 AM, Sebastian Vater wrote:
>> Vitor Sessak a écrit :
>>
>>> I don't know what typical values are, but is the folowing doable?
>>>
>>> #define MAX_INSTRUMENTS [... some value here ...]
>>> AVSequencerInstrument *instrument_list[MAX_INSTRUMENTS];
>>>
>>> Everything access and insertion O(1) and both done in one line of
>>> code...
>>
>> The limit almost always 64k, which would be quite large in that case.
>
> I don't mean the theoretical limit, I mean the biggest value ever used
> in any actual file.

Hmm, and how to determine that? Including all the future files that will
ever be created?

Another possibility would be simply stick to 2^n size, with a start
let's say of 1, and if we add a new instrument which makes the list
larger or equal to (2^n) + 1, we increase the size to 2^(n+1).

Anyway, when the limit is 64k, we have at worst O(65535) which should
even not a problem for 20 year old CPUs. And even if the user has to
wait half a second here, we can accept this (in that case, the user
would simply add 16 instruments at once to avoid the delay).

>
>> But I have another idea, we have a CONFIG_SMALL option right?
>>
>> We could do my idea, if CONFIG_SMALL is defined and when it's undefined
>> we use your MAX_INSTRUMENTS approach?
>
> No, the whole point of a MAX_INSTRUMENTS is to make things simpler and
> this would ruin it.

Ok idea discarded. ;-)

>>
>> Remember that the unknown data is only unknown to TuComposer/FFmpeg, the
>> GUI editor / whatever calling it might know (partially or fully) the
>> data, but to find these, the data has to be organized some way. My
>> thoughts on this were, that the applications search this list, match
>> their identifier and then evaluate just their data.
>
> I don't really like to incentive the behavior of adding
> application-specific data to the files...

Unfortunately, some do this, and chunk based files like RIFF/IFF are
especially designed for that. Expect to find this, even the IFF-ILBM
most popular paint program (DPaint) did this.

I'm not 100% sure about this, but MIDI files edited by professional
sequencers like CuBase probably also store extra data in these,
sometimes even important for final song output (i.e. adding custom
samples this way).

-- 

Best regards,
                   :-) Basty/CDGS (-: