doc/ffmpeg,ffmpeg-formats: avoid to mention ffmpeg options from formats.texi

Also extends documentation for timestamp related ffmpeg options, in order
to make more apparent the fact that muxer processing may change the
timestamps values.

doc/ffmpeg-formats.texi

@@ -151,11 +151,6 @@ been without shifting.
 
 Also note that this affects only leading negative timestamps, and not
 non-monotonic negative timestamps.
-
-When avoid_negative_ts is used together with copyts, vsync or async then
-avoid_negative_ts is applied last. This is neccessary so that containers
-which do not support negative timestamps wont get any and can be used
-with vsync/async and copyts.
 @end table
 
 @c man end FORMAT OPTIONS

doc/ffmpeg.texi

@@ -902,6 +902,10 @@ Chooses between 1 and 2 depending on muxer capabilities. This is the
 default method.
 @end table
 
+Note that the timestamps may be further modified by the muxer, after this.
+For example, in the case that the format option @option{avoid_negative_ts}
+is enabled.
+
 With -map you can select from which stream the timestamps should be
 taken. You can leave either video or audio unchanged and sync the
 remaining stream(s) to the unchanged one.
@@ -911,6 +915,11 @@ Audio sync method. "Stretches/squeezes" the audio stream to match the timestamps
 the parameter is the maximum samples per second by which the audio is changed.
 -async 1 is a special case where only the start of the audio stream is corrected
 without any later correction.
+
+Note that the timestamps may be further modified by the muxer, after this.
+For example, in the case that the format option @option{avoid_negative_ts}
+is enabled.
+
 This option has been deprecated. Use the @code{aresample} audio filter instead.
 
 @item -copyts
@@ -919,7 +928,8 @@ to sanitize them. In particular, do not remove the initial start time
 offset value.
 
 Note that, depending on the @option{vsync} option or on specific muxer
-processing, the output timestamps may mismatch with the input
+processing (e.g. in case the format option @option{avoid_negative_ts}
+is enabled) the output timestamps may mismatch with the input
 timestamps even when this option is selected.
 
 @item -copytb @var{mode}