Patent Application
20190238931
This application claims the benefit of Taiwan application Serial No. 107103617, filed Feb. 1, 2018, the subject matter of which is incorporated herein by reference.
The invention relates to Digital Video Broadcasting (DVB), and more particularly to a de-jitter buffer in a DVB receiving end.
The development of digital video broadcasting has gradually matured with the progressing of communication technologies. The Digital Video Broadcasting (DVB) standard is one mainstream digital video broadcasting standard in African and Asian regions.
The de-jitter buffer 107 serves a main purposes of buffering data sequentially outputted from the de-interleaving and FEC circuit 106, combines the data into a transport stream, and transmits the transport stream at an appropriate speed to the source decoder 108. If the de-jitter circuit 107 outputs the transport stream without waiting for a period of time after receiving a first set of data, subsequent data in the transport stream may not be ready yet for output after the first set of data because the speed at which the de-interleaving and FEC circuit 106 stores the data into the de-jitter buffer 107 is not fast enough. Such issue is referred to as underflow. Conversely, if the de-jitter buffer 107 starts outputting the transport stream too slowly, storage space in the de-jitter buffer 107 for accommodating the data stored thereinto by the de-interleaving and FEC circuit 106, causing an issue of overflow.
According to the specification of the DVB standard, a transmitting end provides a time-to-output (TTO) parameter to the de-jitter buffer 107 at the receiving end for each interleaved video frame, wherein the TTO parameter indicates a starting time point for the de-jitter buffer 107 to output the transport stream corresponding to the interleaved video frame.
However, in actual conditions, it is a common problem that a transmitting end does not provide a reasonable TTO parameter to a receiving end. For example, some transmitting ends sets TTO parameters of all interleaved video frames to zero. If a receiving end uses these TTO parameters without checking, the abovementioned issue of underflow may be encountered, severely affecting the normal operation of the receiving end.
To solve the above issues, the present invention provides a signal receiving apparatus and a signal processing method.
A signal receiving apparatus is provided according to an embodiment of the present invention. The signal receiving apparatus receives a video signal provided by a Digital Video Broadcasting (DVB) transmitting end, wherein the video signal corresponds to multiple interleaved video frames. The signal receiving apparatus includes a time de-interleaver, a signal processing circuit, a verification circuit, a de-jitter buffer, a correction circuit and a setting circuit. The time de-interleaving circuit performs time de-interleaving on the multiple interleaved video frames to generate a time de-interleaving result, and generates a counting request upon identifying an interleaved video frame under verification. The signal processing circuit performs signal processing on the time de-interleaving result to generate a signal processing result. The signal processing has an average delay. The de-jitter buffer obtains an original time-to-output (TTO) of the interleaved video frame under verification from the signal processing result, accordingly generates an output request, and transforms the signal processing request to a transport stream. The verification circuit generates a counting result according to the counting request and the output request, and determines, according to the counting result and the average delay, whether a TTO under verification of the interleaved video frame under verification satisfies a predetermined condition. If the TTO under verification does not satisfy the predetermined condition, the correction circuit generates a corrected TTO under verification, and requests the verification circuit to verify whether the corrected TTO under verification satisfies the predetermined condition. If the TTO under verification satisfies the predetermined condition, the setting circuit sets, according to the TTO under verification, a time to output the transport stream for the de-jitter buffer.
A signal processing method applied to a Digital Video Broadcasting (DVB) receiving end is provided according to another embodiment of the present invention. The method includes: a) receiving a video signal provided by the DVB receiving end, wherein the video signal corresponds to multiple interleaved video frames; b) performing time de-interleaving on the multiple interleaved video frames to generate a time de-interleaving result, and generating an output request upon identifying a starting point of an interleaved video frame under verification; c) performing signal processing on the time de-interleaving result to generate a signal processing result, wherein the signal processing has an average delay; d) obtaining an original time-to-output (TTO) of the interleaved video frame under verification from the signal processing result, and accordingly generating an output request; e) transforming the signal processing result to a transport stream; f) generating a counting result according to the counting request and the output request, and determining whether a TTO under verification of the interleaved video frame under verification satisfies a predetermined condition according to the timing result and the average delay; g) if the TTO under verification does not satisfy the predetermined condition, generating a corrected TTO under verification, and verifying whether the corrected TTO under verification satisfies the predetermined condition; and h) if the TTO under verification satisfies the predetermined condition, setting, according to the TTO under verification, a time to output the transport stream.
The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.
It should be noted that, the drawings of the present invention include functional block diagrams of multiple functional modules related to one another. These drawings are not detailed circuit diagrams, and connection lines therein are for indicating signal flows only. The interactions between the functional elements/or processes are not necessarily achieved through direct electrical connections. Further, functions of the individual elements are not necessarily distributed as depicted in the drawings, and separate blocks are not necessarily implemented by separate electronic elements.
As previously described, for each interleaved video frame, a transmitting end provides a time-to-output (TTO) parameter for reference of the de-jitter buffer 207. In practice, a transmitting end may provide unreliable TTO parameters for quite a few consecutive interleaved video frames. It is known that, if one TTO parameter acquired by the de-jitter buffer 207 is deemed unreasonable, following TTO parameters of other subsequent interleaved video frames are much likely unreasonable. Thus, in the signal receiving apparatus 200, the verification circuit 211 first verifies a TTO parameter (to be referred to as an original TTO parameter (TTO_TX)) that a transmitting end provides for one certain interleaved video frame to determine whether to initiate a subsequent correction procedure. More specifically, if the verification circuit 211 determines that the original time to output TTO_TX satisfies a predetermined condition, the verification circuit 211 requests the setting circuit 213 to set, according to the original time to output TTO_TX, a starting time point at which the de-jitter buffer 207 outputs the transport stream. Conversely, if the verification circuit 211 determines that the original TTO TTO_TX does not satisfy the predetermined condition, the correction circuit 212 generates a corrected TTO, and requests the verification circuit 211 to again perform verification to determine whether the corrected TTO satisfies the predetermined condition. Only when the corrected TTO satisfying the predetermined condition has been successfully identified, the setting circuit 213 sets, according to the corrected TTO, a starting time point for outputting the transport stream for the de-jitter buffer 207.
The predetermined condition used by the verification circuit 211, and implementation details of the verification circuit 211, the correction circuit 212 and the setting circuit 213 are given in the embodiments below.
The time spending on signal processing processes in the signal processing circuit 206B contribute an implementation delay, which is also referred to as a transmission latency. An average (to be referred to as an average delay imp_delay) of the implementation delay may be generated through simulation calculations or actual measurements, and is pre-stored in a memory (not shown) of the signal receiving apparatus 200. It should be noted that, the value of the average delay imp_delay may differ as a signal format (e.g., an encoding mode) changes; average delays imp_delay corresponding to multiple different signal formats may be pre-stored in the signal receiving apparatus 200 to serve as reference information for the verification circuit 211.
In this embodiment, the verification circuit 211 includes a timing circuit 211A, an addition circuit 211B, a comparison circuit 211C and a multiplexer 211D. The timing circuit 211A counts a working time length Cnt. As shown in
It should be noted that, details of how the timing de-interleaver 206A identifies a starting point of an interleaved video frame and how the de-jitter buffer 207 acquires the original TTO TTO_TX are generally known to one person skilled in the art, and shall be omitted herein. On the other hand, although the output request is received to generate a counting result tto_Cnt, the counting circuit 211A continues counting. The working time length Cnt accumulated by the counting circuit 211A is provided to the setting circuit 213 for further use, with associated details to be given shortly.
As previously described, the average delay imp_delay contributed by the signal processing circuit 206B is known in advance. The addition circuit 211B receives the average delay imp_delay, and calculates a summation result Sum of the average delay imp_delay and a TTO under verification. As shown in
In this embodiment, the predetermined condition used by the verification circuit 211 is set as “the addition result Sum of the average delay imp_delay and the TTO under verification needs to be greater than the counting result tto_Cnt”. Thus, the comparison circuit 211 compares the values of the addition result Sum with the counting result tto_Cnt. More specifically, the transmitting end usually sets the original TTO TTO_TX according to the time spent in an encoding process; however, the time spent in a decoding procedure at a receiving end is usually longer than the time spent in the encoding process at the transmitting end. For example, it costs some time for trial-and-errors in signal processing of the signal processing circuit 206B that is not within the period covered by the original TTO TTO_TX, and so the average delay imp_delay is taken into account. With the average delay imp_delay added, a reasonable/reliable original TTO TTO_TX allows the condition “the addition result Sum_0 is greater than the counting result tto_Cnt_0” to be met.
A scenario where “the addition result Sum_0 is greater than the counting result tto_Cnt_0” is first discussed. When the verification result outputted by the comparison circuit 211C indicates that the original TTO TTO_TX satisfies the above predetermined condition, the correction circuit 212 is idling, and the setting circuit 213 sets, according to the original TTO TTO_TX, a starting time point of outputting the transport stream for the de-jitter buffer 207. In this case, the time to output of the de-jitter buffer 207 is set to be equal to the addition result Sum_0 of the original TTO TTO_TX and the average delay imp_delay. As shown in
In practice, for two successive interleaved video frames time having same timing interleaving depth and encoding mode, the time to output of these two interleaved video frames do not differ much. If the time interleaving depth and encoding mode of multiple successive interleaved video frames are the same, it can be inferred that the TTOs of these interleaved video frames are close to one another. Thus, when it is determined that the original TTO TTO_TX of the initial interleaved video frame is reliable, it is not necessary for the verification circuit 211 to continue verifying the original TTO of the subsequent interleaved video frames one after another. More specifically, the setting circuit 213 can set, on the basis of the original TTO TTO_TX of the initial interleaved video frame, the same TTO for the following successive interleaved video frames, for the de-jitter buffer 207 to output the corresponding transport streams.
It should be noted that, the time point set by the setting circuit 213 for the de-jitter buffer 207 to output the transport stream may not be exactly equal to the addition result Sum_0. For example, the decoding time lengths of the interleaved video frames may slightly vary. Thus, the time the de-jitter buffer 207 outputs the transport stream may be slightly greater than the addition result Sum_0 so as to cover the variances in the decoding time lengths of the subsequent interleaved video frames. Setting the addition result Sum_0 greater than the counting result tto_Cnt_0 as the time point at which the setting circuit 213 generates the output request ensures the de-jitter buffer 207 from being underflow. On the other hand, an upper limit of the time to output that the setting circuit 213 generates does not cause overflow of the de-jitter buffer 207. One person skilled in the art can understand that, given that the time to output that the setting circuit 213 generates is set within an appropriate range, the de-jitter buffer 207 will not suffer from underflow or overflow. That is to say, the time point at which the setting circuit 213 generates the output request is flexible to a certain extent.
A scenario where “the addition result Sum_0 is smaller than or equal to the counting result tto_Cnt_0” is discussed below. When the verification result outputted from the comparing circuit 211C indicates that the original TTO TTO_TX does not satisfy the predetermined condition, the correction circuit 212 receives an instruction and accordingly generates a corrected TTO TTO′_1. In practice, the transmitting end may refer to a time interleaving depth TI of an interleaved video frame when generating a original TTO TTO_TX. Thus, in one embodiment, the correction circuit 212 uses the time interleaving depth TI of an interleaved video frame as the corrected TTO TTO′_1. Taking the DVB-T2 standard for instance, the time interleaving depth TI may be an integral multiple (e.g., three times) of a time length of one T2 video frame, or may be a fraction of an integer (e.g., one-third) of a time length of one T2 video frame. The correction circuit 212 may calculate the time interleaving depth TI of an interleaved video frame received by the signal receiving apparatus 200 according to information provided by the transmitting end. Associated calculation details are generally known to one person skilled in the art, and shall be omitted herein. The correction circuit 212 may store the above time interleaving depth TI in advance, or may obtain this information from a parsing result of the de-jitter buffer 207. When the verification result outputted from the comparing circuit 211C indicates that the original TTO TTO_TX does not satisfy the predetermined condition, the multiplexer 211D feeds the corrected TTO TTO′_1 into the addition circuit 212B, and the corrected TTO TTO′_1 is added with the average delay imp_delay to obtain the addition result Sum_1. Another possibility is that the correction circuit 212 stores the corrected output time TTO′_1 into the de-jitter buffer 207, and so the addition circuit 212B may fetch the corrected TTO TTO′_1 from the de-jitter buffer 207. In other words, when the interleaved video frame under verification is not the initial interleaved video frame but is a subsequent interleaved video frame, the TTO under verification is the corrected TTO TTO′ generated by the correction circuit 212.
In one embodiment, if the verification circuit 211 determines that the original TTO TTO_TX does not hold the predetermined condition true, the de-jitter buffer 207 is reset; that is, the de-jitter buffer 207 discards data associated with the initial interleaved video frame, and again starts receiving data associated with the next interleaved video frame. Further, the timing circuit 211A is reset to generate a counting result tto_Cnt for the next interleaved video frame. More specifically, the timing circuit 211A starts counting upon identifying the starting point of the next interleaved video frame, and outputs the counting result when the de-jitter buffer 207 acquires the original TTO TTO_TX of the interleaved video frame. After the timing circuit 211A outputs the counting result tto_Cnt (to be represented by tto_Cnt_1) of the next interleaved video frame, the comparison circuit 211C compares values of the counting result tto_Cnt_1 with the addition result Sum (i.e., the addition result of the corrected TTO TTO′_1 and imp_delay). If the addition result Sum_1 is greater than the counting result tto_Cnt_1, it means that the corrected TTO TTO′_1 holds the predetermined condition true, and this verification result drives the setting circuit 213 to set the time to output for the de-jitter buffer 207 to output the transport stream. For example, the setting circuit 213 can set, according to the addition result Sum_1, the time to output that causes the de-jitter buffer 207 to output the transport stream of multiple successive subsequent interleaved video frames.
If the verification result outputted by the comparison circuit 211C indicates that the corrected TTO TTO′_1 does not hold the predetermined condition true, the correction circuit 212 generates another corrected TTO TTO′_2 that is greater than the corrected TTO TTO′_1. In practice, the correction circuit 212 may slightly increase the corrected TTO each time till the corrected TTO satisfies the predetermined condition. In one embodiment, the correction circuit 212 calculates an allowed increment according to the capacity of the de-jitter buffer 207 and the output rate of the transport stream, and adds the allowed increment to the interleaving depth TI as the corrected TTO TTO′_2. For example, the correction circuit 212 may configure the allowed increment to correspond to a quarter of the capacity of the de-jitter buffer 207. Assuming that the capacity of the de-jitter buffer 207 is 2 MB and the output rate of the transport stream is 1 MB of data per 7/64 ms, so that the de-jitter buffer 207 outputs data of a quarter of its capacity every 7/128 ms. In this situation, 7/128 ms is the above allowed increment, and the corrected TTO TTO′_2 is the addition result of the time interleaving depth TI and 7/128 ms.
Similarly, the addition circuit 211B calculates an addition result Sum_2 of the corrected TTO TTO′_2 and the average delay imp_delay, and the comparison circuit 211C compares the addition result Sum_2 with a counting result tto_Cnt_2 corresponding to the next interleaved video frame to accordingly determine whether the corrected TTO TTO′_2 satisfies the predetermined condition. If the addition result Sum_2 is greater than the counting result tto_Cnt_2, the setting circuit 213 may set, according to the corrected TTO′_2, the time to output the transport stream for the de-jitter buffer 207. Conversely, if the addition result Sum_2 is smaller than the counting result tto_Cnt_2, the correction circuit 212 continues generating another corrected TTO TTO′_3 greater than the corrected TTO′_2, and so forth.
In the above embodiment, when the TTO under verification does not meet the predetermined condition, the de-jitter buffer 207 discards data associated with the interleaved video frame under verification, and the next interleaved video frame is selected as a new interleaved video frame under verification. In this situation, the corrected TTO TTO′ generated by the correction circuit 212 is for the use of the new interleaved video frame under verification, i.e., used as the TTO under verification of the new interleaved video frame under verification. For example, if the original TTO TTO_TX of the initial interleaved video frame does not meet the predetermined condition, the corrected TTO TTO′_1 generated by the correction circuit 212 is for the use of the new interleaved video frame under verification (i.e., the subsequent interleaved video frame but not the initial interleaved video frame). If the corrected TTO TTO′_1 meets the predetermined condition, the setting circuit 213 sets, according to the corrected TTO TTO′_1, the time to output the transport stream associated with the subsequent interleaved video frame for the de-jitter buffer 207.
In another embodiment, when the TTO under verification does not meet the predetermined condition, the de-jitter buffer 207 does not discard the data associated with the current interleaved video frame under verification. In this situation, the corrected TTO TTO′ generated by the correction circuit 212 is for the use of the current interleaved video frame that is under verification, and serves as a new TTO of this interleaved video frame. For example, if the original TTO TTO_TX of the initial interleaved video frame does not hold the predetermined condition true, the corrected TTO TTO′_1 generated by the correction circuit 212 is still for the use of the initial interleaved video frame, and serves as a new TTO under verification of the initial interleaved video frame. Only when the TTO under verification which meets the predetermined condition is found, the de-jitter buffer 207 can accordingly output the transport stream associated with the initial interleaved video frame.
One person skilled in the art can appreciate that, operation variations in the description associated with the signal receiving apparatus 200 are applicable to the signal processing method in
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 107103617 | Feb 2018 | TW | national |
