Due to the possibility to connect to two or more streams simultaneously with different clocks synchronization It's necessary to improve the timestamps calculation to detect this.
Prior to this commit, we saved the first timestamp that arrive and use it to calculate the running time of the stream for the rest of frames (pts field in gstreamer buffer) in all of the streams. This lead to problems when connecting to multiple streams in multiple computers and the clocks were not correctly synchronized.
To fix this, now we save a different initial timestamp for each stream.
See: https://github.com/FFmpeg/FFmpeg/blob/master/libavdevice/libndi_newtek_common.h#L27
From NDI SDK Documentation:
This is the timecode of this frame in 100ns intervals. This is generally not used internally by the SDK, but is passed
through to applications who may interpret it as they wish. When sending data, a value of
NDIlib_send_timecode_synthesize can be specified (and should be the default), the operation of this value is
documented in the sending section of this documentation. NDIlib_send_timecode_synthesize will yield UTC
time in 100ns intervals since the Unix Time Epoch 1/1/1970 00:00. When interpreting this timecode a receiving
application may choose to localise the time of day based on time zone offset which can optionally be communicated by
the sender in connection metadata. Since timecode is stored in UTC within NDI, communicating timecode time of day for
non UTC time zones requires a translation
We could also go via the glib::Type but that requires more steps unless
we also add a getter from the registered type to the audio/video source
modules.
A buffer can also have one or both of a start and an end offset. These are media-type specific. For video buffers, the start offset will generally be the frame number. For audio buffers, it will be the number of samples produced so far. For compressed data, it could be the byte offset in a source or destination file. Likewise, the end offset will be the offset of the end of the buffer. These can only be meaningfully interpreted if you know the media type of the buffer (the preceding CAPS event). Either or both can be set to GST_BUFFER_OFFSET_NONE.
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer/html/GstBuffer.html
Now it's possible to connect to N streams in the same pipeline. Each new connection will create a new NDI receiver except if it's a empty slot in the receiver.
Each receiver has two slots one to connect to audio and other to connect to video to the same stream.
