ffmpeg HLS multisize with no audio - audio

Question

I need to implement HLS video conversion and I've found a shell script that works almost perfectly. Here it is:
VIDEO_IN=test.mov
VIDEO_OUT=master
HLS_TIME=4
FPS=25
GOP_SIZE=100
PRESET_P=veryslow
V_SIZE_1=960x540
V_SIZE_2=416x234
V_SIZE_3=640x360
V_SIZE_4=768x432
V_SIZE_5=1280x720
V_SIZE_6=1920x1080
# HLS
ffmpeg -i $VIDEO_IN -y \
-preset $PRESET_P -keyint_min $GOP_SIZE -g $GOP_SIZE -sc_threshold 0 -r $FPS -c:v libx264 -pix_fmt yuv420p \
-map v:0 -s:0 $V_SIZE_1 -b:v:0 2M -maxrate:0 2.14M -bufsize:0 3.5M \
-map v:0 -s:1 $V_SIZE_2 -b:v:1 145k -maxrate:1 155k -bufsize:1 220k \
-map v:0 -s:2 $V_SIZE_3 -b:v:2 365k -maxrate:2 390k -bufsize:2 640k \
-map v:0 -s:3 $V_SIZE_4 -b:v:3 730k -maxrate:3 781k -bufsize:3 1278k \
-map v:0 -s:4 $V_SIZE_4 -b:v:4 1.1M -maxrate:4 1.17M -bufsize:4 2M \
-map v:0 -s:5 $V_SIZE_5 -b:v:5 3M -maxrate:5 3.21M -bufsize:5 5.5M \
-map v:0 -s:6 $V_SIZE_5 -b:v:6 4.5M -maxrate:6 4.8M -bufsize:6 8M \
-map v:0 -s:7 $V_SIZE_6 -b:v:7 6M -maxrate:7 6.42M -bufsize:7 11M \
-map v:0 -s:8 $V_SIZE_6 -b:v:8 7.8M -maxrate:8 8.3M -bufsize:8 14M \
-map a:0 -map a:0 -map a:0 -map a:0 -map a:0 -map a:0 -map a:0 -map a:0 -map a:0 -c:a aac -b:a 128k -ac 1 -ar 44100\
-f hls -hls_time $HLS_TIME -hls_playlist_type vod -hls_flags independent_segments \
-master_pl_name $VIDEO_OUT.m3u8 \
-hls_segment_filename HLS/stream_%v/s%06d.ts \
-strftime_mkdir 1 \
-var_stream_map "v:0,a:0 v:1,a:1 v:2,a:2 v:3,a:3 v:4,a:4 v:5,a:5 v:6,a:6 v:7,a:7 v:8,a:8" HLS/stream_%v.m3u8
It works as expected when test.mov has an audio track. But if it is, e.g. a screencast recorded with Quick Time with no audio track it will fail with this error:
Stream map 'a:0' matches no streams.
To ignore this, add a trailing '?' to the map.
I tried to do what it recommends and add ? to all audio mappings like:
-map a:0?
In this case it failed on -var_stream_map because it doesn't allow optional parameters.
I've also found how to add an empty audio track here adding silent audio in ffmpeg
But I had no luck trying to combine it with the script above.
Can anyone help me change the script so it could accept any files with and without audio?
p.s. I honestly read the official docs of ffmpeg but it didn't help at all

Answer 1

It seems this is due to the HLS muxer not parsing/using the trailing '?'. Unfortunately, there is currently nothing you can do differently in your call to ffmpeg.
The work around I use is to call
ffprobe -show_streams -select_streams a -i $VIDEO_IN
If the resulting list of STREAMS is empty, then there is no audio stream.
Then you can adjust your ffmpeg call accordingly.