Retrieve one frame at a time sequentially

Use getFrameAtIndex sequentially and retrieve one frame at a time,
MediaMetadataRetriever internally will reuse the decoder and frame
memory in this case. This is as efficient and holds up less shared
memory (as we only need one temp frame).

bug: 120414514
Change-Id: I58ddc5df63edaf480875ce2651bf18a037793aad