[Live-devel] Understanding testOnDemandRTSP

[Kumar Bala (DSP-Weuffen GmbH)]

Hi,
I am using the ByteStreamFileSource as an example to implement
frameread. But I noticed something fishy.
I run the testOnDemandRTSPServer on one machine (montavista linux on
DM355) and try to play it at the client side (Windows PC) using VLC

There was an initial delay , so i added some printfs to see what is
happening. I added a printf in the file ByteStreamFileSource.cpp before
the line
FILE* fid = OpenInputFile(env, fileName);

to see if the file is opened multipletimes to even be played once and
the log

fopen instance 1
Read Data fFrameSize 150000
Read Data fFrameSize 135519
Read Data fFrameSize 142284
Read Data fFrameSize 141502
Read Data fFrameSize 146454
Read Data fFrameSize 145149
Read Data fFrameSize 143908
Read Data fFrameSize 146148
Read Data fFrameSize 148311
Read Data fFrameSize 144188
Read Data fFrameSize 142923
Read Data fFrameSize 146860
Read Data fFrameSize 144253
Read Data fFrameSize 145276
Read Data fFrameSize 17033
fopen instance 2
Read Data fFrameSize 150000
Read Data fFrameSize 135519
Read Data fFrameSize 142284
Read Data fFrameSize 141502
Read Data fFrameSize 146454
Read Data fFrameSize 145149
Read Data fFrameSize 143908
Read Data fFrameSize 146148
Read Data fFrameSize 148311
Read Data fFrameSize 144188
Read Data fFrameSize 142923
Read Data fFrameSize 146860
Read Data fFrameSize 144253
Read Data fFrameSize 145276
Read Data fFrameSize 17033

As you can see the file is opened TWICE !!! But then if i try to play it
any further it opens the file only once. Only at the first instance it
does a complete file read !?! Is it a bug at the client end ?

Ross Finlayson wrote:
>> Hi,
>> I am trying to understand and modify one of the testProgs -
>> testOnDemandRTSP
>> Below is how I understand the flow (pardon my lack of OOD understanding)
>>
>>   testOnDemandRTSPServer ->  ServerMediaSession ->
>> MPEG4VideoFileServerMediaSubsession ->   
>> FileServerMediaSubsession->  ByteStreamFileSource
>>
>> Instead of using a file as an input source I would like to use the
>> output of a "blocking function", which gives one output MPEG4 frame
>> every call. This function captures a V4L2 frame from a capture device
>> and encodes it into a MPEG4 frame. Which is the right point where I
>> should insert this blocking function ?
>
> You should first write your own subclass of "FramedSource" that
> encapsulates your capture device.  (See "DeviceSource.cpp" for a model
> of how to do this.)
>
> Then, you should write your own subclass of "ServerMediaSubsession" -
> that uses your new 'capture device' class (instead of
> "ByteStreamFileSource") - and use this in place of
> "MPEG4VideoFileServerMediaSubsession".