HTTP Video Streaming Header Requirements

Problem

HTML5 video elements fail to play with "Failed to load video" error even though network requests show successful 200/206 responses. The video file downloads correctly when tested with curl, but browsers refuse to play it.

Context / Trigger Conditions

• Video element fires onerror event despite network success
• DevTools Network tab shows 200 or 206 status for video requests
• curl -O <video-url> downloads a valid MP4 file
• Video plays locally when downloaded
• Error message is generic: "Failed to load video" or media error code 4

Solution

Required Headers for Video Streaming

1. Accept-Ranges: bytes (CRITICAL)

   • Tells browser that range requests are supported
   • Without this, browsers may not attempt range requests for seeking
   • Add to ALL video responses, even full (200) responses

2. Content-Type: video/mp4 (or appropriate MIME type)

   • Must match actual video format
   • Browser uses this to select decoder

3. Content-Length (for full responses)

   • Required for browser to know file size
   • Enables progress indicators and seeking calculations
   • Note: For 206 responses, this should be partial content size

4. For Range Requests (206 Partial Content):

   • Content-Range: bytes START-END/TOTAL
   • Status code MUST be 206, not 200

Server Implementation

// Fastly Compute@Edge example
resp.set_header("Accept-Ranges", "bytes");
resp.set_header("Content-Type", "video/mp4");

// For full responses only (not 206):
if resp.get_status() != StatusCode::PARTIAL_CONTENT {
    resp.set_header("Content-Length", file_size.to_string());
}

CDN Considerations

• Edge caches may strip or modify headers
• Verify headers reach the client, not just origin
• Fastly/CloudFront can serve range requests from cached full content
• Test with curl -I -H "Range: bytes=0-1023" to verify 206 response

Verification

# Check Accept-Ranges header
curl -I https://cdn.example.com/video.mp4 | grep -i accept-ranges
# Expected: accept-ranges: bytes

# Test range request support
curl -I -H "Range: bytes=0-1023" https://cdn.example.com/video.mp4
# Expected: HTTP/2 206 with Content-Range header

# Verify partial download works
curl -H "Range: bytes=0-100" https://cdn.example.com/video.mp4 | wc -c
# Expected: 101 (bytes 0-100 inclusive)

Example

Before (broken):

HTTP/2 200
content-type: video/mp4
x-custom-header: value

Video fails to load in browser.

After (working):

HTTP/2 200
content-type: video/mp4
content-length: 1443199
accept-ranges: bytes

Video plays correctly with seeking support.

Notes

• Even if your CDN handles range requests automatically, you should still include Accept-Ranges: bytes in the response headers
• Some browsers are more forgiving than others; Safari often requires proper range support while Chrome may work without
• HTTP/2 responses may have headers lowercased (this is normal)
• For HLS/DASH streaming, the manifest and segments all need proper headers
• Mobile browsers are particularly strict about video headers

References

• MDN: Range Requests
• MDN: Accept-Ranges
• HTTP 206 Partial Content