Add keyframe index metadata
Used to facilitate seeking; particularly for HTTP pseudo streaming.
1. read live streaming or file by sequence
2. if use add_keyframe_index option, add a mark flag at the position,
use to insert new context at the last step.
3. add the keyframes *offset* and *timestamp* into a list
4. if use add_keyframe_index option, shift the metadata data from
mark flag offset
5. insert the keyframes *offset* and *timestamp* from the list by
sequence
6. free the list
7. end.
Add FATE test case;
Reviewed-by: Lou Logan <lou@lrcd.com>
Signed-off-by: Steven Liu <liuqi@gosun.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
