Abstract:
A method for reproducing, i.e., playing back, media data includes: receiving media data in a receive buffer; determining whether the receive buffer is sufficiently filled; reducing the playback speed over a period until the receive buffer is sufficiently filled, and playing back the media data at the reduced playback speed. The reduced playback speed has a speed profile having at least one non-linear section.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a method for reproducing media data, a media reproduction apparatus and a vehicle. 
       BACKGROUND TO THE INVENTION 
       [0002]    Vehicles, such as automobiles, involve the use of a large number of apparatuses that are used to receive and reproduce media, such as radio programs, television programs and telephone calls. In this case, digital media data are stored in a reception buffer following reception in order to compensate for the usually discontinuous transmission of digital data in packets. 
         [0003]    When digital audio data and/or video data are transmitted from a source to the sink, for example, a stable and interference-free reproduction practically always requires buffering of the data at a receiver end in order to compensate for fluctuations during the data transmission (jitter). Since the buffer first needs to be filled, particularly before the beginning of reproduction, reproduction usually starts after a delay. This becomes noticeable when changing over from one audio stream to another, for example. 
         [0004]    A similar problem can arise when different media sources need to be synchronized. An example that may be mentioned is an automobile radio that can receive the same radio station either in analog form using FM or in digital form using DAB. So as always to be able to provide the listener with the best (that is to say: interference-free) sound quality, the radio can change over between reproduction of the analog signal and the digital signal on a case by case basis. For technical reasons, the audio signal may be subject to a time delay between the two cited reception paths. Should it be desirable to perform the changes as actually as possible, matching therefore needs to take place in the receiver by delaying the leading signal by means of buffering. In this case, the problem again arises that the selected audio source cannot be reproduced immediately but rather the reception buffer is first of all filled. 
         [0005]    For the time for the buffering, either the audio signal from a previous source continues to be reproduced or the reproduction is muted. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the invention to render the reproduction of digital media more agreeable to a listener/viewer. 
         [0007]    This object is achieved by the subject matter of the independent claims. Further embodiments of the invention are obtained from the dependent claims and from the description below. 
         [0008]    One aspect of the invention relates to a method for reproducing digital media data. By way of example, the media data may comprise audio data and/or video data. 
         [0009]    According to one embodiment of the invention, the method comprises the steps of:
       reception of media data in a reception buffer;   establishment of whether the reception buffer is filled;   reduction of the reproduction speed over a period of time until the reception buffer is sufficiently filled; and   reproduction of the media data at the reduced reproduction speed.       
 
         [0014]    By way of example, the digital media data are received in data packets that are first of all stored in a reception buffer. If the reception buffer is empty or no longer sufficiently filled to be able to ensure continuous reproduction of the media data at a normal reproduction speed, the reproduction speed is temporarily reduced, so that the media data are reproduced more slowly when new media data arrive. This allows the reception buffer to fill. 
         [0015]    By way of example, a situation in which the reception buffer is not sufficiently filled may arise when a program or a media stream is changed, as is the case when changing a radio program, for example. Such a situation can also arise when reproduction of the media data is started, for example at the beginning of media reproduction, such as when a headset is switched on. In all of these situations, the media reproduction can start immediately when the first media data from the selected media source arrive at the receiver. 
         [0016]    According to one embodiment of the invention, the reduced reproduction speed has a speed profile having at least one nonlinear section. In other words, the change in the reproduction speed over time does not need to be constant, but rather can increase or decrease. In this way, transitions between reproduction speeds that are greatly different than one another can be compensated for more harmonically. 
         [0017]    If just a comparatively small reception buffer needs to be filled, a moderate speed change can suffice. If a large buffer needs to be filled in a short time, however, it may be unavoidable for the slowing of the reproduction to be apparent. In this case, the speed change can also be highlighted as an “effect” in which the speed profile at the reduced reproduction speed is modeled. 
         [0018]    By way of example, this can be accomplished by making the reproduction speed similar to that of a tape drive starting to turn or to a record player that is speeding up. 
         [0019]    In this way, the time that is needed to fill a reception buffer can be concealed without this requiring a signal from an incorrect media source having to be reproduced or the media reproduction having to be muted. 
         [0020]    According to one embodiment of the invention, the speed profile has a section in which the reproduction speed increases more than linearly. In other words, the reproduction speed increases over time, with the change in the reproduction speed over time increasing as time goes by. By way of example, this allows a transition between a low reproduction speed, which may be almost zero, and a reproduction speed that corresponds almost to the normal reproduction speed to be modeled. This transition can be modeled as in the case of a starting analog reproduction appliance. 
         [0021]    According to one embodiment of the invention, the speed profile has a section in which the reproduction speed increases less than linearly. In other words, the reproduction speed increases over time, with the change in the reproduction speed over time decreasing as time goes by. By way of example, this allows a transition between a reproduction speed that corresponds almost to the normal reproduction speed and the normal reproduction speed to be modeled. 
         [0022]    According to one embodiment of the invention, the method also comprises the step:
       overlaying of the media data with a media effect when the reproduction speed has been reduced.       
 
         [0024]    In order to strengthen the impression of a starting reproduction appliance server, it is possible, by way of example, for an audio signal to be overlaid with further tones, for example the crackling of a record player or the sound of a turning tape drive. In this way, it is possible to bridge the time with the actual (but slowed) audio signals and to make this as acceptable as possible to the listener, if need be, by adding audio effects. 
         [0025]    A further option is for the audio signal not to be put through to the loudspeakers immediately but rather to be delayed by one second, for example. This allows the buffer to be filled for one second. So as not to hear silence from the loudspeakers for one second, the typical sound of a radio that is tuning through the VFH frequency band can be played. A tuner today is usually so fast that practically no delay arises as a result of tuning. The tuning sound may therefore be an audio sample that is simply played at the appropriate time. In the case of reception appliances with an analog dual tuner, (while one tuner is already at the target frequency and filling the buffer) the second tuner can tune through the band and produce the typical effect. 
         [0026]    According to one embodiment of the invention, the method also comprises the step of:
       matching of a pitch to the reduced reproduction speed.       
 
         [0028]    If the media data comprise audio data, the audio data can be reproduced such that the pitch is increased by the same factor as the reproduction speed is reduced. Appropriate signal processing allows the pitch, which may be distorted as a result of the speed change, to be corrected. In this way, slight changes should be apparent only to a few listeners. 
         [0029]    According to one embodiment of the invention, the media data are transmitted via a wireless link. The wireless link may comprise a radio link and/or an infrared link. By way of example, radio programs can be transmitted via a digital radio link. It is also possible for a data transmission from a radio receiver to a set of headphones to be effected via an infrared link. 
         [0030]    A further aspect of the invention relates to a media reproduction apparatus for reproducing media data. By way of example, the media reproduction apparatus may be a radio tuner, an automobile radio, a head unit, i.e. a main unit, which may be located in the central console of a vehicle, or a set of headphones. 
         [0031]    According to one embodiment of the invention, the media reproduction apparatus comprises a reception device for receiving digital media data, for example a radio receiver or an infrared receiver; a reception buffer for buffer-storing received media data; and a reproduction device for reproducing media data from the reception buffer. By way of example, the reproduction apparatus may comprise a loudspeaker or a display. 
         [0032]    The media reproduction apparatus can carry out the method as claimed in one of the preceding claims, i.e. reduce the reproduction speed of the media data when the reception buffer needs to be filled, for example. It goes without saying the features of the method as described above and below may also be features of the media reproduction apparatus, and vice versa. 
         [0033]    A further aspect of the invention relates to a vehicle having a media reproduction apparatus, as described above and below. By way of example, the vehicle may be an automobile, truck, motorcycle or bus. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0034]    Exemplary embodiments of the invention are described in detail below with reference to the accompanying figures. 
           [0035]      FIG. 1  shows a vehicle having a media reproduction apparatus according to an embodiment of the invention. 
           [0036]      FIG. 2  shows a flowchart for a method for reproducing media data according to an embodiment of the invention. 
           [0037]      FIG. 3  shows a speed profile for the reproduction of media data according to an embodiment of the invention. 
       
    
    
       [0038]    In principle, identical or similar parts are provided with the same reference symbols. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0039]      FIG. 1  shows a vehicle  10  having media reproduction apparatuses  12   a ,  12   b , in the form of an automobile radio or a head unit  12   a  and a set of headphones  12   b.    
         [0040]    The automobile radio  12   a  or the head unit  12   a  can receive digital and analog radio programs via a radio link  14   a  using a reception device (tuner)  16   a  and can reproduce said radio programs via a reproduction device  18   a  in the interior of the vehicle  10 , for example via loudspeakers. 
         [0041]    The media data from a digital radio program are stored in a reception buffer  20   a  prior to reproduction before being processed further by the reproduction device  18   a  and converted into an analog signal. 
         [0042]    As an alternative to reproduction in the interior of the vehicle  10 , the media data can be transmitted in digital form via an infrared link  14   b  or a radio link  14   b  to the reception device  16   b  of the set of headphones  12   b . There, the media data are buffer-stored in a reception buffer  20   b  and output to an ear loudspeaker by a reproduction device  18   b.    
         [0043]      FIG. 2  shows a flowchart for a method for reproducing media data that can be carried out by the automobile radio  12   a , or the head unit  12   a , or the set of headphones  12   b.    
         [0044]    In a step  30 , media data are received in a reception buffer  20   a ,  20   b . By way of example, the media data are received by the automobile radio  12   a  or the head unit  12   a  and particularly the tuner  16   a  via the radio link  14   a  and buffer-stored in the reception buffer  20   a . Similarly, the reception device  16   b  of the set of headphones  12   b  can receive media data via the link  14   b  and buffer-store said media data in the reception buffer  20   b.    
         [0045]    In a step  32 , it is established whether the reception buffer  20   a ,  20   b  is sufficiently filled. By way of example, the reception buffer may be sufficiently filled if it is at least 80% filled or it contains media data for at least the next two seconds. 
         [0046]    If the reception buffer  20   a ,  20   b  is sufficiently filled, the media data are reproduced at normal reproduction speed by means of the reproduction apparatus  18   a ,  18   b  in a step  34 . 
         [0047]    If the reception buffer  20   a ,  20   b  is not sufficiently filled, the reproduction speed is reduced over a period of time in a step  36 . In this case, the period of time may be chosen such that the reception buffer is sufficiently filled again at the end of the period of time. By way of example, the period of time has a predefined length. 
         [0048]    By way of example, a driver of the vehicle  10  can switch on the automobile radio  12   a  and select an analog FM station. The automobile radio  12   a  recognizes that the same radio station can also be received in digital quality using DAB, but with a time delay of three seconds. The automobile radio  12   a  or the head unit  12   a  then reduces the reproduction speed smoothly to 95%. As a result, in one minute the reception buffer  20   a  can be filled with three seconds. A seamless change between DAB and FM is then possible. 
         [0049]      FIG. 3  shows a graph with a possible speed profile  50  for the reproduction of media data. In step  36 , to reduce the reproduction speed, the speed profile  50  with at least one nonlinear section  52 ,  54  is produced or selected. 
         [0050]    By way of example, the speed profile  50  is stored in the corresponding reproduction apparatus  12   a ,  12   b  or calculated therein. 
         [0051]    In the graph, time t is plotted to the right and reproduction speed v is plotted upward. In this case, a reproduction speed of 100% corresponds to a normal reproduction speed. 
         [0052]    In the graph, it can be seen that the speed profile  50  has reduced speeds during a period of time  56 . In this period of time  56 , the reproduction speed rises nonlinearly from 0% to 100%. In a first section  52 , the reproduction speed has a positive curvature and the gradient of the curve increases. In a second section  54 , the reproduction speed has a negative curvature and the gradient of the curve decreases. In this way, it is possible to achieve a continuous transition for the reproduction speeds in the period of time  56 . 
         [0053]    The speed profile  50  can additionally be modeled such that the effect of a starting analog reproduction appliance, such as a tape drive or a record player, arises. 
         [0054]    In a step  38 , the media data are reproduced at reduced reproduction speed by means of the reproduction apparatus  18   a ,  18   b . In addition, a media effect, such as crackling, can be overlaid with the reproduced media data in this step. The media effect may be stored in the corresponding media reproduction apparatus  12   a ,  12   b.    
         [0055]    The reception device  16   a  or the radio tuner  16   a  can be located in a separate tuner box, for example, that supplies the head unit  12   a  with a desired radio program by means of a digital audio stream. 
         [0056]    The head unit  12   a  or the set of headphones  12   b  contains a reception buffer  20   b  of three seconds, for example. 
         [0057]    The radio listener in the vehicle  10  can then change the tuned station. The tuner box or the reception device  16   a  starts sending the new audio stream or the audio data to the head unit  12   a  or the reproduction apparatus  18   a  thereof. The latter uses the first data packets that arrive to output an audio signal. Since the audio data may still have interference or be incomplete (the stabilizing reception buffer  20   b  is not yet filled at this time), the audio signal is mixed with the sound of a pickup coming down onto a record in order to conceal any interference. In addition, the speed profile  50  is used to simulate the reproduction speed of a record starting to turn. This slowing allows the reception buffer  20   b  to be filled with at least one second fairly quickly, which is sufficient for fairly interference-free operation. Within the next minute, the reception buffer  20   b  is filled to a target level by virtue of the reproduction speed of the audio signal initially remaining indistinguishably reduced. 
         [0058]    In addition, it should be pointed out that “comprising” does not exclude other elements or steps, and “a” or “an” does not exclude a large number. Furthermore, it should be pointed out that features or steps that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps from other exemplary embodiments described above. 
         [0059]    Reference symbols in the claims should not be regarded as a restriction.