Specify JPEG XL codestream encapsulation.

draft-avtransport-spec.bs

@@ -3640,6 +3640,66 @@ This structure is flexible enough to permit zero-copy or one-copy streaming
 of video from most sources.
 
 
+### JPEG XL codestream encapsulation ### {#jxl-encapsulation}
+
+For JXL codestream streams, the [=codec_id=] in the
+[[#stream-registration-packets]] must be ''0x4a584c20'' (''JXL '').
+
+JXL streams require no [[#stream-configuration-packets]]. A JXL stream may
+optionally contain a [[#stream-configuration-packets]]. The payload of such
+a packet MUST start with a <code>u(32)</code> configuration identifier.
+
+The only supported configuration identifier is ''0x6a786c6c'' (''jxll'').
+The remainder of the configuration payload contains a <code>u(8)</code>
+integer which equals the level of the signalled codestreams.
+
+If a receiver receives an unsupported configuration identifier, it SHOULD
+ignore it.
+
+If no ''jxll'' stream configuration packet is present, codestreams are
+assumed to be level 5.
+
+The [=packet_data=] must contain a fragment of a JXL codestream. The
+codestream Signature, SizeHeader, ImageMetadata, and encoded ICC profile
+(if present) as well as any trailing zeroes needed to pad to a byte boundary,
+these MUST be sent first as a whole packet, and the frame type MUST be
+FRAME_TYPE_KEY.
+
+If a preview frame is present in the codestream, it must occur next per [[ISO18181]].
+The entire preview frame is sent as a packet with FRAME_TYPE_S.
+
+The remainder of the JXL codestream is a sequence of one or more Frames, as they are
+defined in [[ISO18181]]. Each Frame is sent in its own packet. A Frame of type kRegularFrame
+or kSkipProgressive is sent as a packet with FRAME_TYPE_C1. A Frame of type kLFFrame
+is sent as a packet with FRAME_TYPE_C2. A Frame of type kReferenceOnly is sent as a packet
+with FRAME_TYPE_C3.
+
+JXL codestreams may optionally be accompanied by JPEG Bitstream Reconstruction Data (JBRD).
+JBRD is not part of a JXL codestream, but it may be sent with a JXL codestream. If JBRD is
+present for a specific codetream, it may be sent as a packet with FRAME_TYPE_C4, but only
+after all other frames for that JXL image have been sent.
+
+All packets for a single JXL image MUST have the same PTS, and they MUST occur in the order
+specified (after being possibly reordered by the receiver).
+
+JXL codestreams encapsulated by this section MUST NOT be animated JXL codestreams. Codestreams
+as used in this section are raw codestreams as defined in ISO181818-1. The container format
+defined in ISO18181-2 is not supported.
+
+If the AVTransport container signals that a JXL image is rotated, it is applied after the
+orientation flag signalled by the JXL codestream.
+
+If a JXL codestream is internally flagged as XYB-encoded, the color information signalled
+by AVTransport SHOULD agree with the color information signalled by the codestream itself.
+If they do not, the color information siganlled by the codestream itself takes precedence.
+
+If a JXL image is internally flagged as not XYB-encoded, the color information signalled
+by AVTransport MUST agree with the color information signalled by the codestream itself.
+
+Animated JXL codestreams are not supported, but may be supported in a future version of this
+standard. If such support does arrive, it will have a separate [=codec_id=].
+
+
 ### Custom codec encapsulation ### {#custom-codec-encapsulation}
 
 A special section is dedicated for custom codec storage. While potentially useful