Whenever av_gettime() is used to measure relative period of time,
av_gettime_relative() is prefered as it guarantee monotonic time
on supported platforms.
Signed-off-by: Martin Storsjö <martin@martin.st>

This avoids the caller having to calculate the byte rate if wanting
to push a file in a rate resembling realtime.
Signed-off-by: Martin Storsjö <martin@martin.st>

Signed-off-by: Martin Storsjö <martin@martin.st>

This reduces the dependency on unistd.h which is not available
on all systems.
Signed-off-by: Mans Rullgard <mans@mansr.com>

Also include stdlib.h explicitly - currently it is used
implicitly via avformat.h.
Signed-off-by: Martin Storsjö <martin@martin.st>

Without this, the end of the file might not be transmitted/written.
Signed-off-by: Martin Storsjö <martin@martin.st>

It also optionally can throttle its operation to a particular
speed, to simulate realtime writing.
Signed-off-by: Martin Storsjö <martin@martin.st>