CDN Image/Video Downloads Are Slow — What to Do?

APIYI hosts all generated images and videos on Cloudflare R2’s global CDN. This guide helps you diagnose slow downloads from specific servers.

Quick Answer

All images and videos generated by APIYI (Veo 3.1, Sora, Nano Banana, etc.) are hosted on Cloudflare R2’s global CDN, which is fast worldwide by design. If downloads on your server are slow, it is almost always a network-path issue between your server and Cloudflare’s edge, not a CDN problem itself — especially for servers in mainland China accessing overseas CDNs, where cross-border bandwidth, ISP routing, and local DNS resolution often degrade performance.

Key point

Cloudflare R2 resource URLs typically look like *.r2.cloudflarestorage.com or a custom domain proxied through Cloudflare. Download speed depends on how efficiently your server can reach the nearest Cloudflare edge node.

Common Causes

Cross-border congestion

Servers in mainland China reaching overseas CDNs often hit congestion on international egress during peak hours, causing slowness or timeouts.

Suboptimal ISP routing

Some cloud providers route international traffic through the US West or Europe, adding tens of milliseconds of unnecessary latency.

Poor DNS resolution

Local DNS may resolve Cloudflare hostnames to a distant edge (e.g., US West) instead of the nearest APAC node.

Firewall / security group limits

Some servers restrict outbound traffic to overseas IP ranges, port 443, or specific CDN domains, degrading connection quality.

HTTP/2 & connection reuse

Clients without HTTP/2 or connection reuse pay the TCP/TLS handshake cost for every file.

Single-threaded download

Serial single-threaded downloads can’t benefit from CDN multiplexing; throughput stays low.

Troubleshooting Steps

1. Is it one server or everywhere?

   Try downloading the same CDN URL from your laptop or another server.

   • Laptop fast, server slow → server network path issue
   • Slow everywhere → contact support with the specific URL
2. Test basic network to the CDN

   Use ping, mtr, traceroute to inspect latency and packet loss:

   ping <cdn-host>
   mtr -rwc 30 <cdn-host>
   traceroute <cdn-host>
   

   Packet loss, latency above 200ms, or routes bouncing overseas all indicate link-level problems.

3. Measure real download speed

   Use curl to inspect timing and throughput:

   curl -o /dev/null -w "dns:%{time_namelookup} connect:%{time_connect} \
   ttfb:%{time_starttransfer} total:%{time_total} speed:%{speed_download}\n" \
   "<CDN URL>"
   

   Focus on:

   • time_namelookup: DNS resolution time
   • time_connect: TCP connect time
   • time_starttransfer: Time to first byte (TTFB)
   • speed_download: Average throughput (bytes/sec)
4. Inspect DNS resolution

   dig <cdn-host>
   nslookup <cdn-host>
   

   Check whether the resolved IP is geographically near you. APAC users should get APAC edges; if not, switch to a public DNS.

5. Check server-side restrictions

   Verify that security groups and firewalls allow port 443 and overseas IP ranges, and make sure there’s no egress bandwidth cap in place.

Solutions

Option 1: Switch to a public DNS (easiest)

Default DNS on many servers resolves Cloudflare to distant nodes. Try these public DNS servers:

{/* /etc/resolv.conf */}
nameserver 1.1.1.1        # Cloudflare
nameserver 8.8.8.8        # Google
nameserver 223.5.5.5      # AliDNS
nameserver 119.29.29.29   # DNSPod

Prefer 1.1.1.1 — it’s Cloudflare’s own DNS and reliably resolves to the nearest Cloudflare edge, which is ideal for R2 / Cloudflare CDN traffic.

Option 2: Optimize how you download

Parallel downloads

For batches of files use a parallel downloader (aria2c -x 8, Python asyncio + httpx) to saturate bandwidth.

Resumable downloads

For large videos, use HTTP Range requests with retry so a failure doesn’t restart from zero.

Connection reuse

Use clients with HTTP/2 or keep-alive (httpx, requests.Session()) to avoid repeated handshakes.

Stream to disk

Stream the response directly to disk instead of loading the whole file into memory.

Python example (recommended):

import httpx
import asyncio

async def download(url: str, path: str):
    async with httpx.AsyncClient(http2=True, timeout=120) as client:
        async with client.stream("GET", url) as resp:
            resp.raise_for_status()
            with open(path, "wb") as f:
                async for chunk in resp.aiter_bytes(chunk_size=1024 * 256):
                    f.write(chunk)

asyncio.run(download("<CDN URL>", "output.mp4"))

aria2c example (CLI):

aria2c -x 8 -s 8 -k 1M --file-allocation=none "<CDN URL>"

Option 3: Move to a better-connected region

If your use case allows it, prefer regions with good connectivity to Cloudflare:

Overseas (recommended)

AWS / GCP / Azure / Cloudflare Workers all reach Cloudflare R2 with very low latency (typically 10-50ms).

China: premium DCs

If you must deploy in mainland China, pick DCs with triple-network BGP + premium international links (CN2 GIA, CMI, AS9929).

Hong Kong / Singapore

A good compromise: low latency to mainland China (30-80ms) and excellent APAC Cloudflare connectivity.

Avoid cheap VPS

Budget hosts often have severely congested international egress and can drop to a few dozen KB/s at peak hours. Not recommended for CDN-heavy workloads.

Option 4: Relay through another host (last resort)

If your server really can’t reach Cloudflare quickly and you can’t change regions:

1. Use an overseas server as a relay: download to an overseas box first, then transfer back via a private/premium link
2. Relay via your own object storage: mirror the asset into your own OSS / COS / S3 (e.g., a China-region bucket), and serve from there
3. Pre-warm and cache: download once from your backend and serve subsequent requests from a local cache

Mind the expiration

CDN URLs returned by APIYI for images/videos typically have a limited validity period (see the returned URL). Download and persist assets to your own storage as soon as the callback arrives, to avoid broken links later.

Common Questions

Why is my laptop fast but my server slow?

Home broadband often has optimized international routes via your ISP, while cloud servers go through the datacenter’s international egress — quality can vary dramatically. Check your DC’s international bandwidth first and follow the troubleshooting steps above.

I changed DNS but it's still slow — why?

DNS only affects which CDN edge you resolve to. If the underlying international bandwidth is already congested, DNS changes alone won’t help. Consider changing regions or relaying through an overseas host.

Is Cloudflare R2 blocked in mainland China?

Cloudflare is not blocked in mainland China, but international egress can get congested at peak hours and some ISPs take suboptimal routes, so access quality is inconsistent. This is a general cross-border networking issue, not an R2-specific problem.

Video downloads keep failing — what can I do?

Use a downloader that supports resume, like aria2c or wget -c, with reasonable timeouts and retries:

aria2c -x 8 -s 8 -c --max-tries=10 --retry-wait=3 "<CDN URL>"

Can APIYI return Base64 instead of a CDN URL?

Videos are large (tens to hundreds of MB), and Base64 adds about 33% overhead with no resume support — it’s actually slower and wastes bandwidth. We do not recommend Base64 for large files. Some image endpoints support Base64 responses; see the relevant API docs.

How do I confirm the bottleneck is my network, not the CDN?

Run the same curl test from an overseas host (AWS Tokyo, Singapore, etc.). If it’s fast there but slow on your server, the bottleneck is between your server and Cloudflare — not the CDN itself.

Related Docs

Network Proxy Configuration

Proxy options when international connectivity is unstable

Where are APIYI Servers?

Learn about APIYI server locations and latency

Veo Video Generation API

Output format and URL validity for the video API

Contact Support

If nothing helps, our team will assist you

Info to share with support

When contacting us, please include:

• The specific CDN URL (sensitive params can be masked)
• Your server region / DC / cloud provider
• Full mtr or traceroute output
• Output of the curl timing command above
• The time window when the issue occurred (helps correlate with cross-border link monitoring)