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Extra stream data fixes
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@cyanreg
cyanreg committed Jul 3, 2024
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106 changes: 51 additions & 55 deletions draft-avtransport-spec.bs
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Expand Up @@ -1473,6 +1473,49 @@ Any undefined values are hereby reserved and must not be present in a compliant
AVTransport stream with this version.


### Stream data segmentation ### {#stream-data-segment-packets}

Packets can be split up into separate chunks that may be received out of order
and assembled. This allows transmission over switched networks with a limited MTU,
or prevents very large packets from one stream interfering with another stream.
The packet structure used for segments is the [[#generic-data-segment-packets]] from
[[#generic-data-packets]], with the following descriptors:

<figure id="table-StreamDataSegmentation" class="table">
<table class="complex data longlastcol" dfn-for="#stream-data-segment-packets">
<tr>
<th>Descriptor value</th>
<th>Name</th>
<th>Structure</th>
<th>Description</th>
</tr>
<tr id="0x00FF+0">
<td>''0x00FF''</td>
<td><dfn noexport>stream_data_segment_descriptor</dfn></td>
<td>[[#generic-data-segment-packets]]</td>
<td>Non-final segment for segmented codec configuration.</td>
</tr>
</table>
</figure>

The size of the final assembled packet is the sum of all [=seg_length=] fields,
plus the [=data_length=] field from the [[#stream-data-packets]].

Data segments and packets may arrive out of order and be duplicated.
Implementations must reorder them, deduplicate them and assemble them into
complete packets.

Implementations may try to decode incomplete data packets with missing segments
due to latency concerns.

Senders may send duplicate segments to compensate for packet loss,
but should use [[#fec-grouping-packets]] or [[#stream-data-parity-packets]] instead.

Implementations should discard any packets and segments that arrive after their
presentation time. Implementations should drop any packets and segments
that arrive with unrealistically far away presentation times.


## Extended stream data ## {#extended-stream-data-packets}

Depending upon the codec, using an extended stream data header may be required.
Expand Down Expand Up @@ -1562,54 +1605,48 @@ It is laid out in the following way:
<td>64-bits of LDPC parity data to correct the previous 224 bits of the packet.</td>
</tr>
<tr id="0x0200+12">
<td><code>[=data_length=]*b(8)</code></td>
<td>[=packet_data=]</td>
<td>payload</td>
<td>The packet data itself.</td>
</tr>
<tr id="0x0200+13">
<td><code>i(64)</code></td>
<td>[=duration=]</td>
<td></td>
<td>The duration of this packet in stream timebase unis.</td>
</tr>
<tr id="0x0200+14">
<tr id="0x0200+13">
<td><code>u(32)</code></td>
<td><dfn noexport>total_data_length</dfn></td>
<td></td>
<td>The total size of all data needed to receive the payload correctly. Must be either 0 if unknown, or the total size of the payload across all segments.</td>
</tr>
<tr id="0x0200+15">
<tr id="0x0200+14">
<td><code>u(32)</code></td>
<td><dfn noexport>side_data_length</dfn></td>
<td></td>
<td>Length of the side data, if any.</td>
</tr>
<tr id="0x0200+16">
<tr id="0x0200+15">
<td><code>u(32)</code></td>
<td><dfn noexport>side_data_offset</dfn></td>
<td></td>
<td>The offset within the packet where the side data is located at.</td>
</tr>
<tr id="0x0200+17">
<tr id="0x0200+16">
<td><code>u(8)</code></td>
<td><dfn noexport>side_data_type</dfn></td>
<td></td>
<td>The size of the data in this packet.</td>
</tr>
<tr id="0x0200+18">
<tr id="0x0200+17">
<td><code>b(48)</code></td>
<td>[=padding=]</td>
<td></td>
<td>Padding, reserved for future use. MUST be ''0x0''.</td>
</tr>
<tr id="0x0200+19">
<tr id="0x0200+18">
<td><code>b(64)</code></td>
<td>[=ldpc_288_224=]</td>
<td>[=LDPC(288, 224)=]</td>
<td>64-bits of LDPC parity data to correct the previous 224 bits of the packet.</td>
</tr>
<tr id="0x0200+20">
<tr id="0x0200+19">
<td><code>[=data_length=]*b(8)</code></td>
<td>[=packet_data=]</td>
<td>payload</td>
Expand All @@ -1621,48 +1658,7 @@ It is laid out in the following way:
Extended stream data packets should only be used if there's a need to use them.
Regular stream data packets have a much lower overhead.


### Stream data segmentation ### {#stream-data-segment-packets}

Packets can be split up into separate chunks that may be received out of order
and assembled. This allows transmission over switched networks with a limited MTU,
or prevents very large packets from one stream interfering with another stream.
The packet structure used for segments is the [[#generic-data-segment-packets]] from
[[#generic-data-packets]], with the following descriptors:

<figure id="table-StreamDataSegmentation" class="table">
<table class="complex data longlastcol" dfn-for="#stream-data-segment-packets">
<tr>
<th>Descriptor value</th>
<th>Name</th>
<th>Structure</th>
<th>Description</th>
</tr>
<tr id="0x00FF+0">
<td>''0x00FF''</td>
<td><dfn noexport>stream_data_segment_descriptor</dfn></td>
<td>[[#generic-data-segment-packets]]</td>
<td>Non-final segment for segmented codec configuration.</td>
</tr>
</table>
</figure>

The size of the final assembled packet is the sum of all [=seg_length=] fields,
plus the [=data_length=] field from the [[#stream-data-packets]].

Data segments and packets may arrive out of order and be duplicated.
Implementations must reorder them, deduplicate them and assemble them into
complete packets.

Implementations may try to decode incomplete data packets with missing segments
due to latency concerns.

Senders may send duplicate segments to compensate for packet loss,
but should use [[#fec-grouping-packets]] or [[#stream-data-parity-packets]] instead.

Implementations should discard any packets and segments that arrive after their
presentation time. Implementations should drop any packets and segments
that arrive with unrealistically far away presentation times.
[=side_data_type=] must be ignored if [=side_data_length=] is 0.


## FEC grouping ## {#fec-grouping-packets}
Expand Down

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