Adaptive Bitrate Content Delivery Simulator

Mobile Network

Network class

Volatility (handoffs, congestion) 50%

ABR Algorithm

Safety margin 0.90×

Live Readouts

Throughput now

0.0 Mbps

Buffer

0.0 s

Current tier

–

Rebuffer time

0.0 s

Avg. bitrate played

0.0 Mbps

Quality switches

How it works

Rich mobile content (video, high‑res images, embedded media) is delivered in short chunks, each independently encodable at several quality tiers — a "bitrate ladder". A client‑side ABR (adaptive bitrate) algorithm decides, chunk by chunk, which tier to fetch next.

1. Measure throughput of each finished chunk:
     T_i = chunkSizeBits / downloadTime_i
2. Estimate available bandwidth (harmonic mean
   of the last 5 samples — punishes recent drops
   harder than a plain average):
     T_est = n / Σ(1 / T_i)
3. Apply a safety margin m (< 1 = conservative):
     capacity = T_est × m
4. Pick the highest ladder rung with
     bitrate(rung) ≤ capacity
5. Buffer‑based override: if buffer < 5 s,
   force the lowest rung regardless of (4) —
   protect against a stall over raw quality.

Buffer is seconds of already‑downloaded playback waiting to be shown. It rises by one chunk‑duration each time a chunk finishes, and drains in real time during playback. It caps at 30 s — a full client won't keep prefetching.
Rebuffer / stall happens when buffer hits 0 before the next chunk arrives; playback pauses and only resumes once ~2 s has re‑buffered.
Always Max ignores the network and always requests the top tier — good quality when bandwidth allows it, but it stalls hard the moment throughput drops below that tier's bitrate.
Always Min never stalls but wastes available bandwidth on the lowest quality even on a fast link.

This is the same family of algorithm (throughput‑rule + buffer‑rule) used by real HLS/DASH players and CDN‑backed mobile apps to keep rich content smooth without over‑ or under‑spending a user's mobile data budget.

⏸ REBUFFERING

CDN edge → device Buffer tank Active tier rung

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