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When you want to upload a large file, you can split it into smaller parts and upload them using the Upload Part API.

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Create Upload Session

First, . The resulting object defines the size of each part and the number of parts to upload. 
{
  "id": "F971964745A5CD0C001BBE4E58196BFD",
  "type": "upload_session",
  "session_expires_at": "2012-12-12T10:53:43-08:00",
  "part_size": 1024,
  "total_parts": 1000,
  "num_parts_processed": 455,
  "session_endpoints": {
    "upload_part": "https://upload.box.com/api/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD",
    "commit": "https://upload.box.com/api/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD/commit",
    "abort": "https://upload.box.com/api/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD",
    "list_parts": "https://upload.box.com/api/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD/parts",
    "status": "https://upload.box.com/api/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD",
    "log_event": "https://upload.box.com/api/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD/log"
  }
}

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Split File

Split the file into parts to be uploaded. If you want to use the command line, use the split command: 
split -b <PART_SIZE> <FILE_NAME> <YOUR_PART_NAME>
For example: 
split -b 8388608 video.mp3 videopart
This will result in your file divided into several files.

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Get SHA Digest

To get the value for the SHA digest, use the following openSSL command to encode the file part: 
openssl sha1 -binary <FILE_PART_NAME> | base64
For example: 
openssl sha1 -binary videoparta | base64
The result is a base-64 encoded message used to verify the upload.

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Upload Part

Upload the bytes for the part you want to upload, specifying the byte range for the part and the SHA digest to ensure the content is uploaded correctly. 
curl -i -X PUT "https://upload.box.com/2.0/files/upload_sessions/F971964745A5CD0C001BBE4E58196BFD" \
     -H "authorization: Bearer <ACCESS_TOKEN>" \
     -H "digest: sha=fpRyg5eVQletdZqEKaFlqwBXJzM=" \
     -H "content-range: bytes 8388608-16777215/445856194" \
     -H "content-type: application/octet-stream" \
     --data-binary @<FILE_NAME>

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Content Range

Each part’s size must be exactly equal in size to the part size specified in the upload session that you created. One exception is the last part of the file, as this can be smaller. The Content-Range parameter definition follows this pattern: 
-H "Content-Range: bytes <LOWER_BOUND>-<HIGHER_BOUND>/<TOTAL_SIZE>"
When providing the value for Content-Range, remember that:
  • The lower bound of each part’s byte range must be a multiple of the part size.
  • The higher bound must be a multiple of the part size - 1.
For example, if the part size is 8388608, the content range for the first two parts will be: 
-H "Content-Range: bytes 0-8388607/32127641" \ ## first part
-H "Content-Range: bytes 8388608-16777215/32127641" \ ## second part

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Response

After each upload, the resulting response includes the ID and SHA of the part uploaded. 
{
  "part_id": "6F2D3486",
  "offset": 16777216,
  "size": 3222784,
  "sha1": "134b65991ed521fcfe4724b7d814ab8ded5185dc"
}
Keep all the JSON responses from all part uploads as they are needed to .

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Range Overlap

If a part upload request fails with any error code range_overlaps_existing_part then the application made a mistake in cutting up the file into parts and tried to upload a part into a range that already had content uploaded for it. The application should assume that this last part was not persisted to the session.

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Parallel uploads

Although you can upload the parts in parallel, try to upload them in order as much as is possible. Parts with a lower byte offset should be uploaded before parts with a higher byte offset. The recommended approach is to upload 3 to 5 parts in parallel from a queue of parts, ordered by byte offset. If a part upload fails, retry it before you upload further parts.