28, image decoder 48, audio encoder 26, audio decoder 46, encapsulation unit 30, MMS receiving unit 52, and/or decapsulation unit 50 may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.

Client device 40, server device 60, and/or content preparation device 20 may be configured to operate in accordance with the techniques of this disclosure. For purposes of example, this disclosure describes these techniques with respect to client device 40 and server device 60. However, it should be understood that content preparation device 20 may be configured to perform these techniques, instead of (or in addition to) server device 60.

Encapsulation unit 30 may form Network Abstraction Layer (NAL) units comprising a header that identifies a program to which the NAL unit belongs, as well as a payload, e.g., audio data, video data, or data that describes the transport or program stream to which the NAL unit corresponds. For example, in H.264/AVC, a NAL unit includes a 1-byte header and a payload of varying size. A NAL unit including video data in its payload may comprise various granularity levels of video data. For example, a NAL unit may comprise a block of video data, a plurality of blocks, a slice of video data, or an entire picture of video data. Encapsulation unit 30 may receive encoded video data from video encoder 28 in the form of packetized elementary stream (PES) packets of elementary streams. Encapsulation unit 30 may associate each elementary stream with a corresponding program.

Encapsulation unit 30 may also assemble access units from a plurality of NAL units. In general, an access unit may comprise one or more NAL units for representing a frame of video data, as well as audio data corresponding to the frame when such audio data is available. An access unit generally includes all NAL units for one output time instance, e.g., all audio and video data for one time instance. For example, if each view has a frame rate of 20 frames per second (fps), then each time instance may correspond to a time interval of 0.05 seconds. During this time interval, the specific frames for all views of the same access unit (the same time instance) may be rendered simultaneously. In one example, an access unit may comprise a coded picture in one time instance, which may be presented as a primary coded picture.

Accordingly, an access unit may comprise all audio, 3D media, and/or video frames of a common temporal instance, e.g., all views corresponding to time X. This disclosure also refers to an encoded picture of a particular view as a “view component.” That is, a view component may comprise an encoded picture (or frame) for a particular view at a particular time. Accordingly, an access unit may be defined as comprising all view components of a common temporal instance. The decoding order of access units need not necessarily be the same as the output or display order.

FIG. 2 is a block diagram illustrating elements of an example video file 150. Video file 150 may be included in a message sent according to a messaging service, such as Multimedia Message Service (MMS). Thus, video file 150 may be included in an MMS message. Additionally or alternatively, video file 150 may be included in one or more multimedia messaging body parts (MMBPs) of a multimedia message, which may be an MMS message or other messaging protocol message.

As described above, video files in accordance with the ISO base media file format and extensions thereof store data in a series of objects, referred to as “boxes.” In the example of FIG. 2, video file 150 includes file type (FTYP) box 152, movie (MOOV) box 154, segment index (sidx) boxes 162, movie fragment (MOOF) boxes 164, and movie fragment random access (MFRA) box 166. Although FIG. 2 represents an example of a video file, it should be understood that other media files may include other types of media data (e.g., audio data, timed text data, or the like) that is structured similarly to the data of video file 150, in accordance with the ISO base media file format and its extensions.

File type (FTYP) box 152 generally describes a file type for video file 150. File type box 152 may include data that identifies a specification that describes a best use for video file 150. File type box 152 may alternatively be placed before MOOV box 154, movie fragment boxes 164, and/or MFRA box 166.

MOOV box 154, in the example of FIG. 2, includes movie header (MVHD) box 156, track (TRAK) box 158, and one or more movie extends (MVEX) boxes 160. In general, MVHD box 156 may describe general characteristics of video file 150. For example, MVHD box 156 may include data that describes when video file 150 was originally created, when video file 150 was last modified, a timescale for video file 150, a duration of playback for video file 150, or other data that generally describes video file 150.

TRAK box 158 may include data for a track of video file 150. TRAK box 158 may include a track header (TKHD) box that describes characteristics of the track corresponding to TRAK box 158. In some examples, TRAK box 158 may include coded video pictures, while in other examples, the coded video pictures of the track may be included in movie fragments 164, which may be referenced by data of TRAK box 158 and/or sidx boxes 162.

In some examples, video file 150 may include more than one track. Accordingly, MOOV box 154 may include a number of TRAK boxes equal to the number of tracks in video file 150. TRAK box 158 may describe characteristics of a corresponding track of video file 150. For example, TRAK box 158 may describe temporal and/or spatial information for the corresponding track. A TRAK box similar to TRAK box 158 of MOOV box 154 may describe characteristics of a parameter set track, when encapsulation unit 30 (FIG. 1) includes a parameter set track in a video file, such as video file 150. Encapsulation unit 30 may signal the presence of sequence level SEI messages in the parameter set track within the TRAK box describing the parameter set track.

MVEX boxes 160 may describe characteristics of corresponding movie fragments 164, e.g., to signal that video file 150 includes movie fragments 164, in addition to video data included within MOOV box 154, if any. In the context of streaming video data, coded video pictures may be included in movie fragments 164 rather than in MOOV box 154. Accordingly, all coded video samples may be included in movie fragments 164, rather than in MOOV box 154.

MOOV box 154 may include a number of MVEX boxes 160 equal to the number of movie fragments 164 in video file 150. Each of MVEX boxes 160 may describe characteristics of a corresponding one of movie fragments 164. For example, each MVEX box may include a movie extends header box (MEHD) box that describes a temporal duration for the corresponding one of movie fragments 164.

As noted above, encapsulation unit 30 may store a sequence data set in a video sample that does not include actual coded video data. A video sample may generally correspond to an access unit, which is a representation of a coded picture at a specific time instance. In the context of Advanced Video Coding (AVC), the coded picture include one or more video coding layer (VCL) NAL units, which contain the information to construct all the pixels of the access unit and other associated non-VCL NAL units, such as Supplemental Enhancement Information (SEI) messages. Accordingly, encapsulation unit 30 may include a sequence data set, which may include sequence level SEI messages, in one of movie fragments 164. Encapsulation unit 30 may further signal the presence of a sequence data set and/or sequence level SEI messages as being present in one of movie fragments 164 within the one of MVEX boxes 160 corresponding to the one of movie fragments 164.

SIDX boxes 162 are optional elements of video file 150. That is, video files conforming to the Third Generation Partnership Project (3GPP) file format, or other such file formats, do not necessarily include SIDX boxes 162. In accordance with the example of the 3GPP file format, a SIDX box may be used to identify a sub-segment of a segment (e.g., a segment contained within video file 150). The 3GPP file format defines a sub-segment as “a self-contained set of one or more consecutive movie fragment boxes with corresponding Media Data box(es) and a Media Data Box containing data referenced by a Movie Fragment Box must follow that Movie Fragment box and precede the next Movie Fragment box containing information about the same track.” The 3GPP file format also indicates that a SIDX box “contains a sequence of references to subsegments of the (sub) segment documented by the box. The referenced subsegments are contiguous in presentation time. Similarly, the bytes referred to by a Segment Index box are always contiguous within the segment. The referenced size gives the count of the number of bytes in the material referenced.”

SIDX boxes 162 generally provide information representative of one or more sub-segments of a segment included in video file 150. For instance, such information may include playback times at which sub-segments begin and/or end, byte offsets for the sub-segments, whether the sub-segments include (e.g., start with) a stream access point (SAP), a type for the SAP (e.g., whether the SAP is an instantaneous decoder refresh (IDR) picture, a clean random access (CRA) picture, a broken link access (BLA) picture, or the like), a position of the SAP (in terms of playback time and/or byte offset) in the sub-segment, and the like.

Movie fragments 164 may include one or more coded video pictures. In some examples, movie fragments 164 may include one or more groups of pictures (GOPs), each of which may include a number of coded video pictures, e.g., frames or pictures. In addition, as described above, movie fragments 164 may include sequence data sets in some examples. Each of movie fragments 164 may include a movie fragment header box (MFHD, not shown in FIG. 2). The MFHD box may describe characteristics of the corresponding movie fragment, such as a sequence number for the movie fragment. Movie fragments 164 may be included in order of sequence number in video file 150.

MFRA box 166 may describe random access points within movie fragments 164 of video file 150. This may assist with performing trick modes, such as performing seeks to particular temporal locations (i.e., playback times) within a segment encapsulated by video file 150. MFRA box 166 is generally optional and need not be included in video files, in some examples. Likewise, a client device, such as client device 40, does not necessarily need to reference MFRA box 166 to correctly decode and display video data of video file 150. MFRA box 166 may include a number of track fragment random access (TFRA) boxes (not shown) equal to the number of tracks of video file 150, or in some examples, equal to the number of media tracks (e.g., non-hint tracks) of video file 150.

In some examples, movie fragments 164 may include one or more stream access points (SAPs), such as IDR pictures. Likewise, MFRA box 166 may provide indications of locations within video file 150 of the SAPs. Accordingly, a temporal sub-sequence of video file 150 may be formed from SAPs of video file 150. The temporal sub-sequence may also include other pictures, such as P-frames and/or B-frames that depend from SAPs. Frames and/or slices of the temporal sub-sequence may be arranged within the segments such that frames/slices of the temporal sub-sequence that depend on other frames/slices of the sub-sequence can be properly decoded. For example, in the hierarchical arrangement of data, data used for prediction for other data may also be included in the temporal sub-sequence.

FIG. 3 is a flowchart illustrating an example method of transcoding 3D media data according to the techniques of this disclosure. In the example of FIG. 3, UE A may correspond to content preparation device 20 of FIG. 1, multimedia messaging server may correspond to server device 60 of FIG. 1, and UE B may correspond to client device 40 of FIG. 1.

Initially, UE B may register a device profile with capabilities of UE B with the multimedia messaging server (100). UE A may then send a multimedia message with 3D content (102). The multimedia messaging server may detect that UE B does not support 3D content, and thus, performs transcoding (104). For example, the multimedia messaging server may render the 3D media data into one or more images, and then encode the one or more images. The encoded images may be an HEIF-formatted encoded image sequence. The multimedia messaging server may then send the transcoded message to UE B (106).

FIG. 4 is a block diagram illustrating an example set of devices that may exchange messages including 3D media data according to techniques of this disclosure. In this example, FIG. 4 depicts user equipment (UE) device 120 and UE 122, as well as Multimedia Messaging Server (MMS) 124. MMS 124 and UE 122 are communicatively coupled via radio access network (RAN) 130, in this example. MMS 124 may correspond to an edge computing server.

Initially (e.g., when UE 122 becomes communicatively coupled to RAN 130), UE 122 may send rendering capabilities data (that is, data representing the capabilities of UE 122 to render various types of data, such as image and video data, as well as 3D media data) to MMS 124. In this example, it is assumed that UE 122 is not capable of rendering 3D media data. Therefore, UE 122 may send data to MMS 124 indicating that UE 122 is not capable of rendering 3D media data, but is capable of rendering image data.

At some point, UE 120 and UE 122 may initiate a messaging session, such as a multimedia messaging service (MMS) session. UE 120 may send a message including 3D media data (also referred to herein as 3D object data) to UE 122. MMS 124 may receive this message and determine that the message is destined for UE 122. MMS 124 may determine that the message includes 3D media data. Based on the rendering capabilities data received from UE 122, MMS 124 may extract the 3D media data and render (i.e., transcode) the 3D media data on behalf of UE 122 to image data, then send the 3D media data to UE 122. For example, MMS 124 may update the message received from UE 120 to include the rendered image data instead of the 3D media data. In this manner, UE 122 may be capable of participating in an MMS session including the exchange of 3D media data with UE 120 despite not being capable of locally rendering such 3D media data.

FIG. 5 is a flowchart illustrating an example process of sending transcoded image data to a client device according to techniques of this disclosure. The method of FIG. 5 may be performed by a server device (e.g., a Multimedia Messaging Server (MMS) device), such as server device 60 of FIG. 1 or MMS 124 of FIG. 4. For purposes of explanation and example, the method of FIG. 5 is explained with respect to MMS 124 of FIG. 4.

Initially, MMS 124 receives rendering capability data from a client device (250). The rendering capability data may indicate that the client device is not capable of rendering 3D media data. MMS 124 may then receive a message (e.g., an MMBP message or MMS message) including 3D media data and destined for the client device (252). Based on the rendering capabilities data for the client device, MMS 124 may determine that the client device is not capable of rendering the 3D media data. Thus, MMS 124 may transcode (e.g., render) the 3D media data to image data (e.g., one or more images, such as single image or image sequence) (254), then send the image data to the client device (256).

In this manner, the method of FIG. 5 represents an example of a method of sending media data including: receiving, by a server device, a set of three-dimensional (3D) media data being sent to a client device; transcoding, by the server device, the set of 3D media data to a set of one or more images; and sending, by the server device, the set of one or more images to the client device.

The following clauses represent various examples of the techniques of this disclosure:

- Clause 1. A method of sending media data, the method comprising: receiving, by a server device, a set of three-dimensional (3D) media data being sent to a client device; transcoding, by the server device, the set of 3D media data to a set of one or more images; and sending, by the server device, the set of one or more images to the client device.
- Clause 2. The method of clause 1, further comprising determining that the client device is not capable of rendering the set of 3D media data.
- Clause 3. The method of clause 2, wherein determining that the client device is not capable of rendering the set of 3D media data comprises receiving data representing capabilities of the client device.
- Clause 4. The method of any of clauses 1-3, wherein the client device comprises a first client device, wherein receiving the set of 3D media data comprises receiving the set of 3D media data from a second client device.
- Clause 5. The method of any of clauses 1-4, wherein receiving the set of 3D media data comprises receiving a Multimedia Message Service (MMS) message.
- Clause 6. The method of clause 5, wherein the MMS message is formatted as a multi-part MIME message.
- Clause 7. The method of any of clauses 5 and 6, wherein the MMS message includes a GL Transmission Format (glTF) or a GL transmission Format Binary (glB) file including the 3D media content.
- Clause 8. The method of any of clauses 1-7, further comprising receiving data indicating a recommended camera path along which to render the one or more images.
- Clause 9. The method of clause 8, wherein the recommended camera path includes an initial pose and a set of additional pose and time sample pairs, where each of the additional pose and time sample pairs provides a pose for a virtual camera and a time offset at which to activate the pose.
- Clause 10. The method of clause 8, wherein the recommended camera path includes an initial pose and a description of the recommended camera path including a shape of each segment of the recommended camera path and a velocity of camera movement along the segment.
- Clause 11. The method of any of clauses 1-10, wherein transcoding the 3D media data comprises forming a High Efficiency Image File (HEIF) encoded image sequence including the set of one or more images.
- Clause 12. The method of any of clauses 1-11, wherein transcoding the 3D media data comprises rendering the set of one or more images to include an alpha channel corresponding to portions of the images around one or more 3D objects of the 3D media data.
- Clause 13. The method of clause 1, further comprising determining that the client device is not capable of rendering the set of 3D media data.
- Clause 14. The method of clause 13, wherein determining that the client device is not capable of rendering the set of 3D media data comprises receiving data representing capabilities of the client device.
- Clause 15. The method of clause 1, wherein the client device comprises a first client device, wherein receiving the set of 3D media data comprises receiving the set of 3D media data from a second client device.
- Clause 16. The method of clause 1, wherein receiving the set of 3D media data comprises receiving a Multimedia Message Service (MMS) message.
- Clause 17. The method of clause 16, wherein the MMS message is formatted as a multi-part MIME message.
- Clause 18. The method of clause 16, wherein the MMS message includes a GL Transmission Format (glTF) or a GL transmission Format Binary (glB) file including the 3D media content.
- Clause 19. The method of clause 1, further comprising receiving data indicating a recommended camera path along which to render the one or more images.
- Clause 20. The method of clause 19, wherein the recommended camera path includes an initial pose and a set of additional pose and time sample pairs, where each of the additional pose and time sample pairs provides a pose for a virtual camera and a time offset at which to activate the pose.
- Clause 21. The method of clause 19, wherein the recommended camera path includes an initial pose and a description of the recommended camera path including a shape of each segment of the recommended camera path and a velocity of camera movement along the segment.
- Clause 22. The method of clause 1, wherein transcoding the 3D media data comprises forming a High Efficiency Image File (HEIF) encoded image sequence including the set of one or more images.
- Clause 23. The method of clause 1, wherein transcoding the 3D media data comprises rendering the set of one or more images to include an alpha channel corresponding to portions of the images around one or more 3D objects of the 3D media data.
- Clause 24. A device for retrieving media data, the device comprising one or more means for performing the method of any of clauses 1-23.
- Clause 25. The device of clause 24, wherein the one or more means comprise a processing system including one or more processors implemented in circuitry.