Fix a few "its" vs "it's" typo.

doc/ffserver.texi

@@ -221,7 +221,7 @@ of an infinite movie or a whole movie.
 
 FFM is version specific, and there is limited compatibility of FFM files
 generated by one version of ffmpeg/ffserver and another version of
-ffmpeg/ffserver. It may work but its not guaranteed to work.
+ffmpeg/ffserver. It may work but it is not guaranteed to work.
 
 FFM2 is extensible while maintaining compatibility and should work between
 differing versions of tools. FFM2 is the default.

doc/swresample.txt

@@ -32,9 +32,9 @@ Special Converter         v
                         Output
 
 Planar/Packed conversion is done when needed during sample format conversion.
-Every step can be skipped without memcpy when its not needed.
+Every step can be skipped without memcpy when it is not needed.
 Either Resampling and Rematrixing can be performed first depending on which
-way its faster.
+way it is faster.
 The Buffers are needed for resampling due to resamplng being a process that
 requires future and past data, it thus also introduces inevitably a delay when
 used.

libavcodec/snow.c

@@ -398,7 +398,7 @@ av_cold int ff_snow_common_init(AVCodecContext *avctx){
     int i, j;
 
     s->avctx= avctx;
-    s->max_ref_frames=1; //just make sure its not an invalid value in case of no initial keyframe
+    s->max_ref_frames=1; //just make sure it's not an invalid value in case of no initial keyframe
 
     ff_dsputil_init(&s->dsp, avctx);
     ff_videodsp_init(&s->vdsp, 8);

libavformat/avformat.h

@@ -844,7 +844,7 @@ typedef struct AVStream {
 
     /**
      * Number of internally decoded frames, used internally in libavformat, do not access
-     * its lifetime differs from info which is why its not in that structure.
+     * its lifetime differs from info which is why it is not in that structure.
      */
     int nb_decoded_frames;