How to identify the first I-frame of a H264 stream

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How to Find I-frame Using Wireshark for H.323 Video Communication
Ancient blog post. Skip to the bottom for filter: h264.nal_unit_hdr == 7

There is a sample capture attached to issue 3000: h264 Dissector-errors and extension.
Payload type is 97. Edit->Preferences->Protocol->H.264->H.264 dynamic payload types: 97

Frame 169:

H.264
    NAL unit header or first byte of the payload
        0... .... = F bit: No bit errors or other syntax violations
        .01. .... = Nal_ref_idc (NRI): 1
        ...0 0111 = Type: NAL unit - Sequence parameter set (7)
    H264 NAL Unit Payload