[FFmpeg-devel] patch for DCA "floating point output" option

[madshi]

M?ns Rullg?rd schrieb:
> madshi <dear at madshi.net> writes:
>
>   
>> M?ns Rullg?rd schrieb:
>>     
>>> madshi <dear at madshi.net> writes:
>>>
>>>   
>>>       
>>>> Not sure whether the DCA maintainers will like this patch. But maybe
>>>> they will, so I'm posting it here just in case.
>>>>
>>>> This patch adds optional floating point output to the DCA
>>>> decoder. This optional feature must be enabled at compile time by
>>>> adding the following switch to config.h:
>>>>
>>>> #define CONFIG_AUDIO_NONSHORT 1
>>>>
>>>> I'm using this solution in my eac3to tool because 16bit PCM just
>>>> doesn't cut it for a good audio transcoding tool. The idea for this
>>>> option comes from the MLP/TrueHD decoder which offers a similar
>>>> feature.
>>>>
>>>> +#ifdef CONFIG_AUDIO_NONSHORT
>>>>     
>>>>         
>>> That's a rather useless name.  Can't you think of anything better?
>>>
>>>   
>>>       
>> It was not my idea. The same constant is already used by the
>> MLP/TrueHD decoder. I thought that it doesn't make sense to
>> use a different name for every decoder...
>>
>> Besides, I don't think that the name is useless. Currently the decoders
>> all output "short" samples (shorter than they should be). "non short"
>> simply means that the decoders stop shorten the audio samples.
>>     
>
> The name is equally non-descriptive for any decoder.  If the output is
> not 'short', then what is it?
>   

Well, the point of the constant is to allow the decoder to output
whatever sample format suits best. It may be floating point or
24 bit integer or even the usual 16 bit integer. Of course the
decoder must set the "sample_fmt" field to the correct value.
My patch does that. The MLP/TrueHD decoder does that, too.

A different solution would be to use specific constants for
specific bitdepths/formats. E.g. "CONFIG_AUDIO_FLOAT".
But this doesn't fit every purpose. E.g. lossless audio decoders
should really output their data in the native format. For
MLP/TrueHD that can be either 16 bit integer or 24 bit integer,
but not floating point. For lossy codecs like AC3 and DTS
however the best output format is floating point.

Personally, I want every decoder to output the most ideal
format and bitdepth for the audio track. And this is not the
same for every decoder. So the "non short" flag just tells the
decoder to output what it likes best.