[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:
>>>
>>>   
>>>       
>>>> 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.
>>     
>
> I figured as much, but the name doesn't convey that very well.
> Perhaps something like "native" would be better than "nonshort".
>   

"native" sounds very good to me!

>> 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.
>>     
>
> I agree.  This is how video is handled.  To do this for audio, we'd
> first need a generic way of converting between different sample
> formats.
>   

For ffmpeg yes. For libav not necessarily. Personally, I'm only
using libav and my application can handle any sample format
and bitdepth. So personally I want all libav decoders to always
output in their native format. I understand that for ffmpeg in
its current formt this is problematic, though.