How to used MediaMetadataRetriever for extract frames

[Phonkrit Chanda]

am used MediaMetadataRetriever for extract frames but cannot work
here this code:

            MediaMetadataRetriever retriever = new MediaMetadataRetriever();

            retriever.setDataSource("/sdcard/myvideo.mp4");

            String value =

            retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_DURATION);

            long length = Long.parseLong(value);

            for(int i = 0; i < length; i += 200)

            {

            Bitmap bitmap = retriever.getFrameAtTime(i); <-- problem height and width are -1

            String a = "/sdcard/saved_images/" + i + ".jpg";

           ** save image code **

            }

Thank