Cadence and media content phase alignment

1. A media-playback device for aligning play back of media content for a user performing a running activity, the media-playback device comprising:

a content output device that operates to output media content;

a cadence-acquiring device comprising a movement-determining device and a cadence-determination engine configured to determine a cadence based on movement data captured by the movement-determining device;

a phase-delay calibration engine configured to determine phase delay values for at least one cadence value, wherein the phase-delay calibration engine determines the phase delay values based at least in part on a time required to detect a foot strike within the running activity;

a cadence-based media content selection engine configured to identify a media content item based on the cadence determined by the cadence-acquiring device, wherein the media content item comprises music with a tempo that corresponds to the cadence; and

a phase-aligned media playback engine configured to:

align the identified media content item to the running activity using at least one of the determined phase-delay values; and

cause the media-output device to output the aligned media content item so that a beat of the media content item is output coincidentally with an expected foot strike.

2. The media-playback device of claim 1 , wherein the phase-aligned media playback engine is further configured to:

identify foot strikes within the running activity based on the movement data.

3. The media-playback device of claim 1 , wherein the phase-aligned media playback engine is further configured to:

identify a wave action position within an oscillation of a filtered sequence of measurements captured by the measurement-determining device corresponding to the foot strike based on calculating an orientation of the media-playback device.

4. The media-playback device of claim 1 , wherein the phase-aligned media playback engine is further configured to:

determine a phase delay value corresponding to the determined cadence; and

align the identified media content item to the running activity based on the determined phase delay.

5. The media-playback device of claim 1 , wherein the cadence-based media content selection engine is configured to identify a media content item that includes music with a tempo that is within a predetermined threshold of the cadence.

6. The media-playback device of claim 1 , wherein the cadence-based media content selection engine is further configured to:

monitor for changes in cadence; and

upon detecting a change in cadence:

identify a second media content item based on a changed cadence;

align the second media content item to the running activity; and

cause the media-output device to playback the aligned second media content item.

7. The media-playback device of claim 1 , wherein the measurement-determining device comprises three orthogonally-oriented accelerometers and the cadence-determination engine is configured to:

capture a sequence of measurements from each of the three accelerometers;

filter the sequences of measurements based on frequency to generate filtered sequences;

identify the sequence of measurements corresponding to cadence, wherein the sequence is identified based on calculating energy values for each of the sequences.

8. The media-playback device of claim 1 , wherein the media playback engine is configured to identify wave action positions corresponding to foot strikes.

9. The media-playback device of claim 1 , wherein measurements are captured at a sample rate in the range of 20-200 Hz.

10. The media-playback device of claim 1 , wherein the media content item is stored locally on the media-playback device.

11. The media-playback device of claim 1 , wherein the media content item is streamed to the media-playback device by a media-delivery system based on a request for media content items that specifies the cadence.

12. The media-playback device of claim 1 , wherein the media-playback device is a smartphone.

13. A method of cadence-based media playback for use during repetitive-motion activities comprising:

determining a cadence associated with a repetitive-motion activity based on acceleration data captured by a plurality of accelerometers, wherein the acceleration data comprises sequences of acceleration sample data captured from each of the plurality of accelerometers over a duration of time, the repetitive-motion activity including a repetitive cycle of motion having a repetitive action point;

identifying a media content item based on the determined cadence;

phase aligning the identified media content item to the repetitive-motion activity using a phase delay value, wherein the phase delay value is determined based at least in part on a time required to detect the repetitive action point within the repetitive-motion activity; and

playing back the aligned media content item so that a beat of the media content item is output coincidentally with an expected repetitive action point.

14. The method of claim 13 further comprising:

filtering the sequences of measurements based on frequency to generate filtered sequences;

identifying a cadence signal corresponding to the cadence of the repetitive-motion activity from the filtered sequences; and

analyzing the cadence signal to identify a wave action position corresponding to the repetitive action point within the repetitive-motion activity.

15. The method of claim 14 , wherein analyzing the cadence signal comprises:

identifying a portion of the cadence signal corresponding to an oscillation of the repetitive-motion activity;

determining an orientation of the cadence signal relative to the ground; and

selecting a point within the oscillation that corresponds to the acceleration towards the ground stopping as the wave action position.

16. The method of claim 13 , further comprising:

determining a phase delay value corresponding to the determined cadence; and

aligning the identified media content item to the repetitive-motion activity using the determined phase delay.

17. A method of calibrating a cadence-based media playback device for use during repetitive-motion activities comprising:

generating media output, wherein the media output has a tempo;

determining a cadence associated with a repetitive-motion activity based on acceleration data captured by a plurality of accelerometers, wherein the acceleration data comprises sequences of acceleration sample data captured from each of the plurality of accelerometers over a duration of time, the repetitive-motion activity including a repetitive cycle of motion having a repetitive action point;

determining whether the tempo of the media output corresponds to the determined cadence; and

upon determining that the tempo of the media output corresponds to the determined cadence, calculating a phase delay value for the determined cadence based on the repetitive action point within the repetitive-motion activity and a beat within the media output, wherein the phase delay is determined based at least in part on a time required to detect the repetitive action point within the repetitive-motion activity, and wherein the phase delay indicates a shift in playback of the media output that is needed so that a beat of the media output is output coincidentally with an expected repetitive action point.

18. The method of claim 17 , wherein the tempo of the media output is selected to correspond to a goal cadence selected from a predefined list of cadence values.

19. The method of claim 13 , wherein the repetitive-motion activity includes a running activity.

20. The method of claim 13 , further comprising storing the phase delay value for use in phase aligning media content to a repetitive-motion activity for play back during the repetitive-motion activity.