Last feature: allowing Consumers to seek(?)

[almgong]

As a last DESIRED feature, I would like to add that consumers can seek. See: https://github.com/android/platform_frameworks_base/blob/master/core/java/android/widget/MediaController.java

This entails that:

• the sequence numbers be more meaningful (perhaps they equate to some representation of seconds).
• the mapping of this is somehow transferred to the consumer
• for Consumers only, disable the default controller (is commented out in VideoActivity), and implement a custom SeekBar wherein the user is free to seek as they desire.
• onSeek, the user should update the sequence number to ask for next -- research on mp4 container format to see if this is correct
• Consumers only have the ability to seek, pause, and play video.

[almgong]

It seems more promising to implement this as such:

• create a custom mp4 extractor factory. We do not need to modify the mp4extractor class at all, simply need a handle on the instance in order to call seek() and getPosition(). Perhaps the custom factory returns a singleton (that is created and destroyed on demand).
• create custom play, pause, and seekbar for consumers.
• onSeek, the ui should notify the mp4extractor instance by 1. getPosition() and use to determine what sequence number to send interest for next (no need to "make meaningful"), 2. send an interest with this seq num, 3. then start GetVideoTask again with the next seq num, and 4. call seek() to notify mp4extractor seek occurred.

[almgong]

This will invariably become a next steps - the seeking feature is not consistent.