[Qt-interest] Phonon - Play back a downloading video file

[Jonathan Wong]

Andy, and anyone else interested in this topic of appending to a file while playing it with Phonon...

Experiments show that MediaObject may be seeking around the QIODevice while playing it. Probably
seeked to the end by reading all data there is.

To append to the file, you must seek to the end, even if you opened it with QIODevice::Append. If
you don't do this, "appending" to the file will corrupt it (writing to the wrong position).

Jonathan Wong wrote:
> Hi Andy,
> 
> I tried it, didn't close file, was able to play the file and append to it at the same time.
> 
> However, the total time didn't change. I'll still have to do an enqueue later on. It'll be better
> to use separate file chunks then.
> 
> Qt 4.5. Mpeg, not sure which codec was applied though.
> 
> There seems to be a bug in aboutToFinish signal. To work around it, simply do a setTransitionTime(0).
> 
> Andy Bell wrote:
>> Hi Johathan,
>>
>> No, I don't close the file.  Again, which version of Qt are you using? 
>> What format is the video?
>>
>> Andy
>>
>> On Wed, May 20, 2009 at 11:29 AM, Jonathan Wong <jhannwong at gmail.com
>> <mailto:jhannwong at gmail.com>> wrote:
>>
>>     Hi Andy,
>>
>>     Don't you need to close the 6MB file before you do a setSource?
>>
>>     Of course, it'll be marvelous if I could setSource while still
>>     appending to the same video file.
>>
>>     I just tried it myself. MediaObject is unable to load a video file
>>     if it is not closed. And I
>>     can't open a video file for appending if MediaObject had already
>>     loaded it for playing.
>>
>>     Andy Bell wrote:
>>     > Hi Jonathan,
>>     >
>>     > I guess it may be important here to mention that I am using Qt
>>     4.4.0 on
>>     > Windows XP.
>>     >
>>     > The video files are pretty large, like 700MB, what I find is that
>>     after
>>     > say 6MB of download the video files plays back fine.  This is
>>     obviously
>>     > all dependent on bitrate and the download rate but it seems to work
>>     > fine.  I will try out that signal to see if I can work the player
>>     to run
>>     > smoothly on higher bitrates and/or slower connection speeds.
>>     >
>>     > Andy
>>     >
>>     > On Wed, May 20, 2009 at 6:08 AM, Jonathan Wong
>>     <jhannwong at gmail.com <mailto:jhannwong at gmail.com>
>>     > <mailto:jhannwong at gmail.com <mailto:jhannwong at gmail.com>>> wrote:
>>     >
>>     >     Andy,
>>     >
>>     >     My colleague tried it. Did a MediaObject.setSource(), but
>>     failed to
>>     >     open the file again. Opening
>>     >     the file first will cause setSource() to fail.
>>     >
>>     >     How did you play a video file while it is still open for
>>     appending?
>>     >
>>     >     Jonathan Wong wrote:
>>     >     > Wow, one of my staff told me that wasn't possible, playing video
>>     >     file while still appending to it.
>>     >     > Thanks for the heads up!
>>     >     >
>>     >     > (Sorry, repost. Sent to Andy privately before. The Reply-to
>>     >     doesn't seem to be the list address.)
>>     >     >
>>     >     > Andy Bell wrote:
>>     >     >> Hi All,
>>     >     >>
>>     >     >> I would like to playback a video via Phonon whilst I am
>>     actually
>>     >     >> downloading the video.  I can open the video file and play
>>     it back
>>     >     >> whilst it is downloading but I would like to be able to
>>     have the
>>     >     player
>>     >     >> pause when it reaches the end of the already downloaded
>>     video so that
>>     >     >> more video can be buffered and played back.  Is this possible?
>>     >      If so,
>>     >     >> what do I need to do to accomplish this with Phonon?
>>     >     >>
>>     >     >> Thanks in advance.
>>     >     >>
>>     >     >> Andy Bell
>>     >     >>
>>     >     >>
>>     >     >>
>>     >     >>
>>     >    
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>> -- 
>> Kind regards
>> Andy
>>
>> AllBabel Software
>> www.allbabel.com <http://www.allbabel.com>
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>>
> 
>