[FFmpeg-user] Non-mandatory audio

[Will Boba]

On 10/14/20 11:18 AM, Greg Oliver wrote:
> sorry just realized I had to redirect stderr to get the results
>
> On Wed, Oct 14, 2020 at 10:17 AM Greg Oliver <oliver.greg at gmail.com> wrote:
>
>> On Tue, Oct 13, 2020 at 8:50 AM Mar Andrés López <mar.andres.l at gmv.com>
>> wrote:
>>
>>> Dear all,
>>>
>>>
>>> I am using the following command to generate dash content from a file:
>>>
>>>
>>> ffmpeg -i video.mp4 –r 25 -c:v libx264 -c:a aac -b:a 128k -ac 1 -ar 44100
>>> -map v:0 -b:v:0 2M -map v:0 -b:v:1 145k -map v:0 -b:v:2 365k -map 0:a -f
>>> dash dash.mpd
>>>
>>>
>>> But sometimes I have streams with audio and sometimes not. Is there
>>> anyway to make this command to not break if the video file does not
>>> contains audio?
>>>
>>>
>>> A lot of thanks
>>>
>> Assuming you are scripting this, probe the file first and check for
>> audio.  Use a separate ffmpeg command line for eac result.
>>
>> ffprobe <infile> | grep "Stream.*Audio"
>> if [ $? -eq 0 ]; then
>>      ffmpeg command with audio
>> else
>>      ffmpeg command without audio
>> fi
>>
>
> ffprobe <infile> 2>&1 | grep "Stream.*Audio"
> if [ $? -eq 0 ]; then
>      ffmpeg command with audio
> else
>      ffmpeg command without audio
> fi
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 From here: https://ffmpeg.org/ffmpeg-all.html

"To map the video and audio streams from the first input, and using the 
trailing ?, ignore the audio mapping if no audio streams exist in the 
first input:

ffmpeg -i INPUT -map 0:v -map 0:a? OUTPUT"


Will.