[FFmpeg-devel] [RFC] libavfilter audio API and related issues

Michael Niedermayer michaelni
Fri Jul 2 16:24:36 CEST 2010


On Fri, Jul 02, 2010 at 01:12:41AM -0700, S.N. Hemanth Meenakshisundaram wrote:
> On 07/01/2010 03:14 PM, Stefano Sabatini wrote:
>> On date Friday 2010-06-25 03:52:45 -0700, S.N. Hemanth Meenakshisundaram 
>> encoded:
>>    
>>> Hi All,
>>> [...] Is it ok to name this filter af_resample or should I
>>> name this one af_reformat and reserve the af_resample name for the
>>> sample rate conversion filter?
>>>      
>> Yes I prefer the second scheme:
>> af_reformat
>> af_resample
>>
>>    
>
> Hi Stefano,
>
> I'll rename this as suggested.
>
>> is consistent with the video scale / format filters scheme, maybe even
>> af_format ->  aformat will do.
>>
>>    
>>> 2. The current resample.c only accepts two channel input data - why?
>>> Depending on the file and codec, isn't it possible for input data to
>>> be more than two channels? Can I attempt adding multichannel input
>>> support or is there a reason it is not supported?
>>>      
>> Audio multichannel support is welcome, and I believe is not
>> implemented for historical reasons (the same for which most codecs
>> assume the sample format is always signed 16 bit).
>>    
>
> Did you also get a chance to see my patch from yesterday. The filter now 
> works for the existing channel conversions (if output sample format is 
> 16-bit) and for any sample format conversion. I am now writing a channel 
> conversion routine for downmixing 5.1 audio.
>
> However, the SDL_AudioOpen call configures the audio output to 16-bit 
> signed and stereo output during init. So even though the filter works, I am 
> not able to get SDL to play the audio right unless I set the SDL parameters 
> to the new values in the code and build again. How do I reconfigure SDL 
> whenever channel/sample format changes. Is closing and reopening SDL 
> session acceptable?

ideally SDL should be inited after the audio strutcure is known.
if the audio channels change then yes sdl reinit is ok

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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