[multicat-devel] multicat

[Zdravko Edrovski]

Hello,

I've been working with multicat recently and noticed some problems when concatenating input chunks of video streams, produced also by multicat, back into the original stream and also found what might be the reason for the problem. Please review the explanation bellow and give your comments.

First of all several one minute chunks were produced with the following command:

multicat -u -U -r 1620000000 @multicast_IP output_dir

Then linux command cat was used to rebuild the original stream.
When played back the stream, at the position in time of each join the video was scrambled for very short period (about a second) and then moved on correctly.

I troubleshoot the problem and found that time stamp was not correctly calculated when creating a new file, i.e. function GetDirFile, for a fraction of a second, was returning wrong file name referencing the time in the past. For this reason output stream for really short period of time was alternately written back and forth into two files.
Afterwards everything was back to normal until next file creation.

What I did to remedy the situation was casting the constant 27/1000 to uint64_t type in the function _wall_Date:

Line:
return ((uint64_t)ts.tv_sec * (uint64_t)27000000) + (uint64_t)(ts.tv_nsec * 27 / 1000);

was changed to:
return ((uint64_t)ts.tv_sec * (uint64_t)27000000 + (uint64_t)(ts.tv_nsec) * (uint64_t)0.027 );

It might be that some arithmetic error occurred due to different types.

With this modification we had smooth transition in the output video stream.

Please note that I tried to concatenate the chunks with the multicat command itself, but the output stream was not usable, i.e it was scrambled in some time sequences and time duration was significantly shortened.

System configuration:
OS: Ubuntu 13.10
Multicat release: multicat-2.0

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