ffserver_config: check strchr() return for NULL

Should fix FFmpeg Coverity Scan issue #1257013

Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
ffserver_config: improve error/warning messages

Fix grammar and quote user-supplied values.

Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
ffserver_config: break lines at 80 chars

Add braces when needed and drop redundant parethesis while at it.

Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
ffserver_config: reflow add_codec()

Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
avformat/utils: fix calculating the absolute difference of timestamps

we dont use FFABS(a-b) as that could result in undefined behavior if it overflows

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>