Timestamp H.264 frame ramp up?

[pisymbol .]

Here's a weird thing:

I have a pipeline like so (this is the pertinent part):

... ! omxh264enc bitrate=10000000 ! video/x-h264,
stream-format=(string)byte-stream ! h264parse ! identity name=h264id !
muxer.video_0

I use the "identity" plugin to tap the pipeline and count frames like so:

[
    {
        "delta": 0,
        "frame": 0,
        "timestamp": 769318722
    },
    {
        "delta": 19584421,
        "frame": 1,
        "timestamp": 788903143
    },
    {
        "delta": 6983473,
        "frame": 2,,
        "timestamp": 795886616
    },
    {
        "delta": 8273539,
        "frame": 3,
        "timestamp": 804160155
    },
    {
        "delta": 37436828,
        "frame": 4,
        "timestamp": 841596983
    },
    {
        "delta": 35012695,
        "frame": 5,
        "timestamp": 876609678
    },
    {
        "delta": 32337205,
        "frame": 6,
        "timestamp": 908946883
    },
    {
        "delta": 36766563,
        "frame": 7,
        "timestamp": 945713446
    },
    {
        "delta": 28523040,
        "frame": 8,,
        "timestamp": 974236486
    },
    {
        "delta": 35687439,
        "frame": 9,
        "timestamp": 1009923925
    },

I'm doing a fixed 30fps. However, notice the first few frames have odd
deltas (delta is the difference between the current buf.pts minus the last
frame's buf.pts).

But after about 3-4 frames, my deltas start to look good (~0.03 seconds or
1/30 or 30fps).

For why? Is there some kind of buffering going on I'm not aware of? How can
I avoid this ramp up?

-aps
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