[FFmpeg-user] Need more detailed description of the behaviour of the "-ac <channelcount>" option

[Christoph Gerstbauer]

Am 02.07.2015 um 12:02 schrieb Paul B Mahol:
> On 7/2/15, Christoph Gerstbauer <christophgerstbauer at gmail.com> wrote:
>>
>> Am 02.07.2015 um 11:04 schrieb Paul B Mahol:
>>> On 7/2/15, Christoph Gerstbauer <christophgerstbauer at gmail.com> wrote:
>>>>> Then please don't use it, use an audiofilter instead.
>>>>> (The one that fits your needs.)
>>>>>
>>>>> I am not convinced that the current mapping of -ac
>>>>> to aresample is immutable.
>>>>> (Even if it is, you can still use the filter and
>>>>> you are on the safe side.)
>>>>>
>>>>> Carl Eugen
>>>> Hello Carl, so what can I do when my target has more audio channel than
>>>> the source?
>>>> For example if I have a file with 2ch stereo and my target is 4ch (with
>>>> ch3 and ch4 silent) how can i do that? I need to generate silence for
>>>> the last 2 channels because I dont want to copy ch1ch2 to ch3ch4.
>>>>
>>>> If I have a target with less channels than the source I use the
>>>> -map_channel option:
>>>> Like: ffmpeg -i "24bitaudio8CH.wav" -acodec pcm_s16le -map_channel 0.1.0
>>>> -map_channel 0.1.1 -ac 2 "16bitaudio2CH_ch1ch2.wav"
>>>>
>>>> So is this possible?:
>>>> ffmpeg -i "2ch_audio_source.wav" -i "mono-silence" -acodec pcm_s16le
>>>> -map_channel 0.1.0 -map_channel 0.1.1 -map_channel 1.0.0 -map_channel
>>>> 1.0.0  "4ch_audio_target.wav"
>>>> Is there a filter which can generate silence as input source?
>>> See anullsrc and aevalsrc.
>> Is anullsrc filter about to be debrecated in some years?
>> I think anullsrc will be debrecated because aevalsrc offers mor e
>> possibilities to generate sound or silence.
>> And anullsrc only generates silence.
>>
>> Is this correct?
> Hmm, I do not think it will get deprecated. It should not get deprecated because
> anullsrc is near 10x times faster than aevalsrc in generating silence.
>
>> So would it be better to use aevalsrc (just for generating silence), or
>> are there any known bugs at "aevalsrc"?
> For generating silence anullsrc is much faster.
Thank you, Paul!

Best Regards
Christoph

>> Best Regards
>> Christoph
>>
>>>> Best Regards
>>>> Christoph
>>>>
>>>>
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