We have used in the last article the mediastreamvalidator from Apple to create a report of recommendations for our stream. Now we start fixing this by starting with the following message:
The server MUST deliver playlists using gzip content-encoding
- All Variants
- Master Playlist
I was wondering about this message, because the specification tells me something different:
HTTP servers SHOULD transfer text files — such as Playlists and WebVTT segments — using the “gzip” Content-Encoding if the client indicates that it is prepared to accept it.
Is it now a MUST or a SHOULD? Nevertheless we’ll check how to fix this.
Update: The mediastreamvalidator is not validating it against the RFC specification. It’s validating it against Apples “HLS Authoring Specification for Apple Devices“.
Since I’m using NGINX as my webservice, it has built in support for gzip compression. We just need to enable it by adding the following lines in the nginx.conf:
Enables or disables inserting the “Vary: Accept-Encoding” response header field if the directives gzip, gzip_static, or gunzip are active.
Enables gzipping of responses for the specified MIME types in addition to “text/html”.
application/vnd.apple.mpegurl is the official MIME type for m3u8 playlist files (specified in chapter 4 of RFC 8216). You should also verified that his MIME type is used and correctly sent into the browser. If not, you should verify if the following line is available in your mime.types file:
Restart and Re-Test
After a restart of NGINX (or configuration re-load) we can easily re-execute the mediastreamvalidator and the hlsreport.py to create a new report. Now this point is no longer in your MUST fix list.
Any idea if you can turn on gzip compression for segments? Safari native sends out a header:
Which seems to make gzip not work.
We have a special use case where compressing segments over the wire would be very helpful
Safari sends only “Accept-Encoding: identity” for the media files itself and wants only the playlist files compressed. For the .m3u8 file it sends “Accept-Encoding: gzip”.
The idea behind that is that text file can be well compressed but not binary files like the video or audio stream (.ts files).
Great post! I particularly liked adding multiple outputs and the folders to the stream. It is hard to find technical documents written this well.