Add dual-octet VP8 picture ID to payload descriptor

[Copilot]

Plan for VP8 Dual-Octet Picture ID Implementation

Based on PR #4515, I have applied the following minimal changes:

• Add picture_id field to pjmedia_vpx_packetizer struct in vpx_packetizer.c
• Update payload descriptor size from 1 to 4 bytes for VP8 in vpx_packetizer.c
• Set X bit (0x80) to indicate extended control bits present for VP8
• Set S bit when starting a new partition and increment picture_id
• Set Extended Control Bits ILTK (I bit: 0x80)
• Add dual-octet picture_id to payload descriptor
• Update payload_desc_size in vpx.c for VP8 codec
• Build and test the changes to ensure no regressions
• Address review comments: Update references to Add dual-octet vp8 pictureId to vp8 payload descriptor #4659 and fix formatting

Reference: #4659 (formerly #4515)

Changes Made:

1. vpx_packetizer.c:

   • Added unsigned int picture_id field to pjmedia_vpx_packetizer struct
   • Changed payload_desc_size to conditionally use 4 bytes for VP8 and 1 byte for VP9
   • Set X bit (0x80) to indicate extended control bits
   • Set S bit and increment picture_id when starting new partition
   • Set I bit in Extended Control Bits (0x80)
   • Added dual-octet picture ID encoding with M bit set
   • Fixed comment from H.264 to vpx

2. vpx.c:

   • Updated payload_desc_size to be 4 for VP8 and 1 for VP9

Review Comments Addressed:

• Updated all references from Add dual-octet vp8 pictureId to vp8 payload descriptor #4515 to Add dual-octet vp8 pictureId to vp8 payload descriptor #4659
• Changed payload_desc_size assignment to conditional format: (pktz->cfg.fmt_id == PJMEDIA_FORMAT_VP8? 4: 1)
• Ensured line length does not exceed 80 characters

Validation Results:

• ✅ All changes verified for correctness
• ✅ Line lengths comply with 80-character limit
• ✅ Issue reference updated to Add dual-octet vp8 pictureId to vp8 payload descriptor #4659

The implementation follows RFC 7741 section 4.2 for the dual-octet PictureID format.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add dual-octet vp8 pictureId to vp8 payload descriptor</issue_title>
<issue_description>### Describe the feature

This feature modifies the vp8 packetization method to add the dual-octet picture id to the payload descriptor header. In our usage of vp8, certain systems required this to correctly decode our vp8 media.

Summary of changes:

• We added a picture_id field to the pjmedia_vpx_packetizer struct.
• We increased the size of the vp8 payload descriptor to 4 bytes.
• We increment the picture_id when the S-bit is present
• We set the ILTK Extended Control Bits
• We added the picture id to the two pictureID octets

See https://datatracker.ietf.org/doc/rfc7741/

4.2.  VP8 Payload Descriptor

   The first octets after the RTP header are the VP8 payload descriptor,
   with the following structure.  The single-octet version of the
   PictureID is illustrated to the left (M bit set to 0), while the
   dual-octet version (M bit set to 1) is shown to the right.

         0 1 2 3 4 5 6 7                      0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        |X|R|N|S|R| PID | (REQUIRED)        |X|R|N|S|R| PID | (REQUIRED)
        +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
   X:   |I|L|T|K| RSV   | (OPTIONAL)   X:   |I|L|T|K| RSV   | (OPTIONAL)
        +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
   I:   |M| PictureID   | (OPTIONAL)   I:   |M| PictureID   | (OPTIONAL)
        +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
   L:   |   TL0PICIDX   | (OPTIONAL)        |   PictureID   |
        +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
   T/K: |TID|Y| KEYIDX  | (OPTIONAL)   L:   |   TL0PICIDX   | (OPTIONAL)
        +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
                                       T/K: |TID|Y| KEYIDX  | (OPTIONAL)
                                            +-+-+-+-+-+-+-+-+

The structure modified is shown in the right-hand bit diagram above.

Caveats and limitations

• We did not implmenet the single-octet picture_id format

Contributors:

Zurab Tutberidze (optime.dev)
Tornike Kutchukhidze (optime.dev)
Sergii Lovygin (Trembit)
Jonathan Knowles (Equiti Health)

Describe alternatives you've considered

No response

Additional context

No response</issue_description>

<agent_instructions>Use the patch in #4515.
You must NOT make any modifications other than the reference to the PR number.
</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Add dual-octet vp8 pictureId to vp8 payload descriptor #4659

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