[FFmpeg-user] FFmpeg's HLS variant stream mappings for audio streams

[Ted Park]

> Hello there,
> 
> When dealing with FFmpeg's HLS muxer's handling of audio streams when
> the -var_stream_map option is applied, why is it that an audio stream
> cannot be mapped twice to video streams variant?
> 
> Attempting to do so aborts with the error:
> 
> [hls @ 0x55a6e3f9f7c0] Same elementary stream found more than once in
> two different variant definitions #0 and #1
> [hls @ 0x55a6e3f9f7c0] Variant stream info update failed with status ffffffea
> [tee @ 0x55a6e2ad3e40] Slave
> '[bsfs/a=aac_adtstoasc:bsfs/v=dump_extra:f=hls:hls_wrap=30:hls_time=6:hls_list_size=6:hls_segment_type=fmp4:ignore_io_errors=1:hls_flags=+independent_segments:var_stream_map='v:0,a:0
> v:1,a:0 v:2,a:0 v:3,a:0 v:4,a:0 v:5,a:0 v:6,a:0 v:7,a:0
> v:8,a:0']/home/brainiarc7/Desktop/src/AWEHD/HLS/Gear-%v/manifest.m3u8':
> error writing header: Invalid argument
> [tee @ 0x55a6e2ad3e40] All tee outputs failed.
> 
> Is this limitation by design, and if so, can it be lifted?
> There are cases where re-using outputs, such as common audio streams
> can save significant CPU cycles by eliminating unneccessary
> re-encoding, as demonstrated through the tee muxer.
> 
> The workflow in this case can be replicated with the tee muxer with no
> issue, but with HLS, re-mapping the same audio output to multiple
> variant streams results in error, as shown above.

Can you please post the full command and output rather than an excerpt please?
Since you seem to be using fmp4, did you specify hls_fmp4_init_filename?