X media upload APPEND: 5 MB chunks, and how to split a Sume MP4

On the X API v2, each APPEND request carries one chunk of at most 5 MB, after INIT returns a media_id and before FINALIZE completes the upload. For a Sume MP4, read the file in 5 MB pieces, number each piece as a segment, and upload them in order.

What are the four steps?

The chunked quickstart lists four endpoints.

How many chunks will my file need?

Use 5,000,000 bytes as the chunk size to stay under 5 MB however the vendor counts a megabyte. The script builds a stand-in file, so it runs anywhere; point path at your downloaded MP4 for a real count.

import math, os, tempfile

CHUNK = 5_000_000

def chunks(path):
    with open(path, "rb") as f:
        index = 0
        while block := f.read(CHUNK):
            yield index, block
            index += 1

with tempfile.NamedTemporaryFile(delete=False) as t:
    t.write(os.urandom(12_000_000))
size = os.path.getsize(t.name)
print(size, "bytes ->", math.ceil(size / CHUNK), "chunks")
print([(i, len(b)) for i, b in chunks(t.name)])
os.unlink(t.name)

What does Sume add?

Sume returns a durable media.sume.com MP4, which you download before the upload. The X page says media uploads can fail validation at post time when they exceed the entitlements of the authenticated user, so trim first if the file is close to a limit. A trim job costs $0.02 per the Sume docs.