Audiobook chapters that don't start at beginning of file - sonos

Question

We've implemented a SMAPI service and are attempting to serve up an audiobook. We can select the audiobook and start playback, but we run into issues when we want to move between chapters because our audio files are not split by chapter. Each audiobook is divided into roughly equal-length parts, and we have information on which part and how far into the part each chapter starts.
So we've run into an issue where our getMetadata response is giving back the chapters of the audiobook because that's how we'd like a user to be able to navigate the book, but our getMediaURI responses for each chapter are giving back URLs for the parts the audio files are divided into, and we seem to be unable to start at a specific position in those files.
Our first attempt to resolve the issue was to include positionInformation in our getMediaURI response. That would still leave us with an issue of ending a chapter at the appropriate place, but might allow us to start at the appropriate place. But according to the Sonos docs, you're not meant to include position information for individual audiobook chapters, and it seems to be ignored.
Our second thought, and possibly a better solution, was to use the httpHeaders section of the getMediaURI response to set a Range header for only the section of the file that corresponds to the chapter. But Sonos appears to have issues with us setting a Range header, and seems to either ignore our header or break when we try to play a chapter. We assume this is because Sonos is trying to set its own Range headers.
Our current thought is that we might be able to pass the media URLs through some sort of proxy, adjusting the Sonos Range header by adding an offset to the start and end values based on where the chapter starts in the audio file.
So right now we return <fileUrl> from getMediaURI and Sonos sends a request like this:
<fileUrl>
Range: bytes=100-200
Instead we would return <proxyUrl>?url=<urlEncodedFileUrl>&offset=3000 from getMediaURI. Sonos would send something like this:
<proxyUrl>?url=<htmlEncodedFileUrl>&offset=3000
Range: bytes=100-200
And the proxy would redirect to something like this:
<fileUrl>
Range: bytes=3100-3200
Has anyone else dealt with audio files that don't match up one-to-one with their chapters? How did you deal with it?

Answer 1

The simple answer is that Sonos players respect the duration of the file, not the duration expressed in the metadata. You can't get around this with positionInformation or Cloud Queues.
However, the note that you shouldn't use positonInformation for chapters in an audiobook seems incorrect, so I removed it. The Saving and Resuming documentation states that you should include it if a user is resuming listening. You could use this to start playback at a specific position in the audio file. Did you receive an error when you attempted to do this?
Note that you would not be able to stop playback within the file (for example, if a chapter ended before the file ended). The player would play the entire file before stopping. The metadata would also not change until the end of the file. So, for example, if the metadata for the file is "Chapter 2" and chapter 2 ends before the end of the file, the Sonos app would still display "Chapter 2" until the end of the file.
Also note that the reporting APIs have been deprecated. See Add Reporting for the new reporting endpoint that your service should host.