Video upload with captions doesn't work every time

[antalkiss]

Hi there,

unfortunately it seems captions doesn't appear every time although the video publish API request was successful.

Let me share the details:

Endpoint: uploadBlob
Request and response from the API:

{
  "method": "POST",
  "response": {
    "uri": "at://did:plc:ridw5wciuntrfkqzsz7mh6ti/app.bsky.feed.post/3lfp4f355rr2d",
    "cid": "bafyreihx6uadxoyiicqz3mn2pg6hz2hznlbl7oxgu4jrctn2gb76arngn4",
    "commit": {
      "cid": "bafyreicmtp3kgm53uxd4bju63gti2wqq3i5sfovs5r5ai4rh6c53scv7li",
      "rev": "3lfp4f35flr2d"
    },
    "validationStatus": "valid"
  },
  "request": {
    "repo": "did:plc:ridw5wciuntrfkqzsz7mh6ti",
    "collection": "app.bsky.feed.post",
    "record": {
      "embed": {
        "alt": "",
        "$type": "app.bsky.embed.video",
        "video": {
          "$type": "blob",
          "ref": {
            "$link": "bafkreidcguax5wz7newqcmekfqodkaboyqoqbm5mer7xfos4mrvoko37ty"
          },
          "mimeType": "video/mp4",
          "size": 2107842
        },
        "aspectRatio": {
          "width": 1280,
          "height": 720
        },
        "captions": [
          {
            "file": {
              "ref": {
                "$link": "bafkreicdn5fsslwfhwngicsbysaomkronoxvt65zc3zbl3hfzp5x5bot54"
              },
              "mimeType": "application/octet-stream",
              "size": 148,
              "$type": "blob"
            },
            "lang": "en"
          }
        ]
      },
      "$type": "app.bsky.feed.post",
      "text": "Test video with caption.",
      "createdAt": "2025-01-14T11:08:51+00:00"
    }
  }
}

Post: https://bsky.app/profile/antikiss.bsky.social/post/3lfp4f355rr2d (it can be seen that the subtitle icon doesn't appear)
Video: https://github.com/user-attachments/assets/3b3cd4bb-9bed-4442-b74d-eae1818c5027
Captions file content:

WEBVTT

00:00:00.000 --> 00:00:03.000
It's a beautiful day!

00:00:04.000 --> 00:00:07.000
It is indeed!

00:00:08.000 --> 00:00:10.000
Hello there!

Could you please advise me what i do wrong?

Thank you any suggestion in advance.