Data, Processor, Battery: What Synthesis Costs Compared to Streaming
Short answer: Streaming sends the sound to you, so it costs data. Synthesis makes the sound on your device, so it costs processor work, and on a phone the screen has to stay on. My app wins clearly on data. On battery I don't have a measurement, and I suspect a music app with the screen off does better.
Data: this part is easy
Spotify publishes its own figures. In its apps, Normal quality is about 96 kbit/s, High is about 160, and Very high is about 320.
Turned into an hour of listening, by my own sums:
| Quality | Roughly per hour |
|---|---|
| Normal | 43 MB |
| High | 72 MB |
| Very high | 144 MB |
My app has no audio files. The whole thing is one page of about 170 kilobytes, a small fraction of one megabyte, and it is smaller still once compressed for sending. After it has loaded, the sound needs no more downloading, however long you listen.
To be exact about "no more": the page does keep sending small counts for anonymous analytics. They are tiny next to an audio stream.
Processor: the price of making sound live
A stream arrives finished. Your device only has to unpack it. With synthesis every tone is worked out as it plays, many thousands of values a second for each sound.
I keep that under control in three ways.
- A cap on how many sounds play at once. More on that in voice limits.
- Cleaning up. A sound that has finished is removed, so finished sounds don't pile up. That's in what I clean up after every sound.
- No drawing when nobody is looking. When the tab is in the background the moving picture stops being drawn and only the sound carries on.
I have not measured the processor load properly, so I won't put a figure on it. On the laptops and phones I've tried, it runs without trouble.
Battery: the honest weak spot
On a phone, a web page generally can't keep playing sound once the screen goes dark. So my app asks the phone to keep the screen awake while it plays. The details are in why your phone screen goes dark and the sound stops.
A lit screen uses battery the whole time. A music app can play with the screen off. I haven't measured the difference, but I'd expect the screen to cost more than the sound does. If you're on a phone for hours without a charger, that matters.
Which one when
- Limited mobile data, or a weak connection: synthesis. Nothing has to arrive, so nothing stutters.
- A laptop on a desk: either. The costs are small both ways.
- A phone, for hours, away from a charger: a streaming app with the screen off is probably kinder to the battery.
Sources
Try it: Open Ambient Sound Online and start Ocean. It's free, and after the first moment nothing more needs to download.
Open Ocean, free