The option -hls_enc_key_url actually does not what the docs says

[alexey.rodionov]

According to the docs:

-hls_base_url baseurl
Append `baseurl` to every entry in the playlist. Useful to generate playlists with absolute paths.

-hls_enc_key_url keyurl
If set, `keyurl` is prepended instead of `baseurl` to the key filename in the playlist.

Firstly, actually the baseurl isn't appended to the key filename at all, it's only appended to the segments (chucks) paths.

This can be easily checked by running the following command:

ffmpeg -i input.mp4 -f hls -hls_enc 1 -hls_base_url http://foo.bar/ stream.m3u8

Moreover, baseurl isn't appended to variant playlist paths in the master playlist.

Running the following command:

ffmpeg -i input.mp4 -f hls -hls_enc 1 -hls_base_url http://foo.bar/ -master_pl_name master.m3u8 stream.m3u8

produces the following stream.m3u8 file:

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:4
#EXT-X-MEDIA-SEQUENCE:9
#EXT-X-KEY:METHOD=AES-128,URI="master.m3u8.key",IV=0x00000000000000000000000000000000
#EXTINF:3.883333,
http://foo.bar/stream1.ts
#EXTINF:4.016667,
http://foo.bar/stream2.ts
#EXTINF:0.650000,
http://foo.bar/stream3.ts
#EXT-X-ENDLIST

and the following master.m3u8 file:

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-STREAM-INF:BANDWIDTH=140800,RESOLUTION=1920x1080,CODECS="avc1.64002a,mp4a.40.2"
stream.m3u8

instead of:

#EXTM3U
#EXT-X-VERSION:3
#EXT-X-STREAM-INF:BANDWIDTH=140800,RESOLUTION=1920x1080,CODECS="avc1.64002a,mp4a.40.2"
http://foo.bar/stream.m3u8

And secondly, actually the keyurl isn't prepended to the key filename too, it's actually a filename/path/URL for writing the key file.

Running the following command:

ffmpeg -i input.mp4 -f hls -hls_enc 1 -hls_enc_key_url key.bin stream.m3u8

saves the key file with key.bin name instead of default stream.m3u8.key (by default the key filename depends on the playlist filename).

Running the following command:

ffmpeg -i input.mp4 -f hls -hls_enc 1 -hls_enc_key_url http://foo.bar/ stream.m3u8

causes the following error:

[hls @ 0000026f5cf12000] Opening 'http://foo.bar' for writing
[tcp @ 0000026f637e0c40] Failed to resolve hostname foo.bar: The name does not resolve for the supplied parameters
[out#0/hls @ 0000026f5cf11f00] Could not write header (incorrect codec parameters ?): I/O error

Expected fix:

1. Change the description of the -hls_enc_key_url keyurl option in the docs to what it actually does.
2. Add a new -hls_enc_key_base_url baseurl option for prepending baseurl to the key filename in the playlist (sometimes it's useful to have different baseurl for the key file and for everything else).
3. Fix the -hls_base_url baseurl option so that it adds baseurl not only to the segment (chuck) paths, but also to the variant playlist paths in the master playlist.