[FFmpeg-user] Right audio channel shifted

[Alex]

Moritz Barsnick wrote
> Hi Alex,
> 
>> I guess there is somehing wrong with the channel mapping, but without the
>> fliter_complex the mapping seems to be okay.
> 
> I think the filter_complex messes up the mapping. Note this mapping
> from your output:
>> Stream mapping:
>>   Stream #0:2 (pcm_s24le) -> atrim
>>   atrim -> Stream #0:0 (pcm_s24le)
>>   Stream #0:0 -> #0:1 (copy)
> 
> and this result:
>> Output #0, mxf, to 'test_new.mxf':
>>     Stream #0:0: Audio: pcm_s24le, 48000 Hz, mono, s32 (24 bit), 1152
>> kb/s
>>     Stream #0:1: Video: mpeg2video, yuv422p, 1920x1080 [SAR 1:1 DAR
>> 16:9],
> 
> and this warning:
>> [mxf @ 00000000003b69c0] there must be exactly one video stream and it
>> must be the first one
> 
> I'm sure that's your issue. The filter seems to be messing up the
> mapping, at least in this automatic case.
> 
> Instead of
> 
>> C:\>ffmpeg -i test.mxf -vcodec copy -map 0:v -acodec pcm_s24le -map 0:1
>> -map 0:2 -filter_complex "[a:1]atrim=start=0.035" test_new.mxf
> 
> you probably need something like
> 
> ffmpeg -i test.mxf -vcodec copy -map 0:v -acodec pcm_s24le -map 0:1
> -filter_complex "[a:1]atrim=start=0.035[ashifted]" -map "[ashifted]"
> test_new.mxf
> 
> (Untested) Note that I'm trying to explicitly map the filter output to
> a particular stream, avoiding automatic mapping. You may have to play
> around a bit more with the map options.
> 
> Is this a bug, BTW? Documentation on "-map" states:
>>    The first -map option on the command line specifies the source for
>>    output stream 0, the second -map option specifies the source for
>>    output stream 1, etc.
> 
> Digging further, documentation of "-filter_complex" clarifies:
>>    Output link labels are referred to with ‘-map’. Unlabeled outputs
>>    are added to the first output file.
> 
> So the first documentation section is somewhat unclear, as it is
> "disturbed" by the second behavior. (And in the second section: "first
> output file" -> "first output stream", right?)
> 
> Moritz

Hi Moritz,

thanks for your help, works great! The mapping thing is still a bit
confusing to me. :)

One last problem: I would like to set the sample format of the second stream
back to s32. I tried the follwoing, but it won't work:

ffmpeg -i test.mxf -vcodec copy -map 0:v -map 0:1 -sample_fmt s32 -c:a:0
copy -c:a:1 pcm_s24le -sample_fmt:a:1 s32 -filter_complex
"[a:1]atrim=start=0.035[ashifted]" -map "[ashifted]"  test_new.mxf 

Thanks,
Alex






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