Phonon directShow does not play data from QBuffer or QNetWorkReply

Using phonon with DirectShow or QuickTime backend:

Corrupted or missing video/audio output when setting a QBuffer as MediaSource
-> when QBuffer is still receiving data, it seems like DS and QuickTime backend doesnt take it.

If QBuffer is totally filled with the media data, load and play work as expected.
Otherwise backend will output some part of media (100 ms) and then output black screen.

In example :

• Filling data from QNetworkReply in a QBuffer inside a SLOT connected to the reply downloadProgress .
• if VideoPlayer->load(MediaSource(Qbuffer)) is called before download is finished, the problem occurs.

May it be expected behaviour?