implementing network cache using qiodevice

[derektmm]

Hi,
I am trying to implement an audio HTTP stream player using the phonon framework. I can successfully play local files and even streams using a QUrl or filename as MediaSource, but this is not enough fir what i need.

The goal of my application is to play a live audio stream, that uses authentication. The authentication can be achieved by a normal http username&password, or by setting a certain value in the HTTP User Agent header. The problem is that I cannot use any of these two authentication schemes with the MediaSource url support - I cannot see any username/password support, and I cannot modify the headers of the HTTP connection.

So, I want to do the whole network part manually, connecting to the URL with a QNetworkManager, etc.. which will allow me to set the header and/or use username and password authentication.

My problem is that I think I can make this work (I have written different proof-of-concept parts of the code), but I am left with the problem that this is a live stream, therefore never ends. If I download the stream to a file, and play from there, (which is my current idea) this file will never be truncated and will end up becoming really huge after several days of play. So I need some kind of cache of the stream I'm downloading, which can delete the already played bytes and append the new downloaded bytes to the end.

My question - if this is a correct way to do what I want, which would be the best way to implement this stream cache? Using a QIODevice, as this is what I need to feed to the MediaSource.

Thanks in advance.

[high_flyer]

One way would to use a double buffer.
You fill one while you play the other, once you finished playing, you switch the buffers, and the process starts all over again.

[derektmm]

Without having tested this yet... do you know if its possible to switch the MediaSource without interrupting the playback?

As this is an endless stream, the playback will never 'finish', so I wouldn't have a moment to switch buffers. I would have to set a limit to the size of the buffer (QFIle for example), and when its reached start writing to another. As I allow the buffer to fill to a certain size before starting to play, I would have some time to write data to the new buffer, then detect when the Mediasource has consumed all data from the first buffer, then change the source with MediaSource-> setCurrentSource()

I will test this, thanks for the suggestion. If you already know if such idea can work correctly or not, please let me know.

[high_flyer]

It works well with video... should work for audio too I reckon...

[derektmm]

Hmm... when trying to implement your idea I noticed that the code was not working as expected. I'm writing the downloaded data to a file, opening with QFile and passing the qfile object as MediaSource. But it seems that it is only playing whatever is on the disk at the moment I open it - it doesn't keep reading while the data is written. I am storing a relatively large amount of data, and the bitrate of the stream is low, so I didn't notice this until now.

I realized that QNetworkReply inherits QIODevice, so I tried just passing the QNetworkReply object to the MediaSource, but it results in a segmentation fault....

So I'm pretty much back to square one - do you have experience in such stream-playing code? Could you give me some pointers on how to solve this problem?

Thanks a lot for your responses.

[high_flyer]

But it seems that it is only playing whatever is on the disk at the moment I open it - it doesn't keep reading while the data is written.

I am not sure I follow.
What I meant was:
You load one QIODevice with data and start playing it.
While it is being played, you fill another QIODevice with data (which starts where the first ends).
Once the first QIODevice has come to the end, you set the second one and start playing it, and start filling the first one with data again (from the end of the second), and so on.