Disk I/O for Bitrate Playback

[rhodiel]

I am tying to understand the formula of required disk I/O over bitrate playback. Meaning, if I were to encode a media file with a bitrate of 15 mb/sec ... what is the disk I/O for playing back that video?

[Soopafresh]

Good question, but considering that HD can be played from HD-DVD and BluRay drives, the bottleneck must the system bus, processor, and software codec (especially this one).

[rhodiel]

Thanks for the reply. I am just exploring other avenues and to get more specs regarding how much disk read MB/sec to sustain and SD (15mbps) to an HD (80mbps) files. Will it take a sustained 120 MB/sec playing an SD (15mbps) without any audio hits and/or dropped frames? etc ...

What is the magic formula/equation?

Thanks again.

[jagabo]

Divide by 8. 15 Mb/s --> ~2 MB/s. 80 Mb/s --> 10 MB/s.

[rhodiel]

There you go!!! Many thanks. Are there any other things to consider like latency such as any overheads?

[jagabo]

Latency of hard drives is so much smaller than with DVDs or CDs it's rarely an issue.

You could have problems if your drive falls out of DMA mode. PIO is much slower and consumes a lot of CPU cycles.

Hard drives in external USB enclosures can sometimes be a problem. USB 2.0 maxes out around 20 to 30 MB/s regardless of how fast the drive is. USB 1.1's effective throughput is lower than a 1x DVD.

[rhodiel]

Thank you. This will help me with my projects. If there are any additional info .. please let me know.

Thanks ALL!!!

[BJ_M]

a standard 7200rpm AT type (100) IDE hard drive can EASILY play back a mpeg2 encoded at 50-80meg/s (10 times dvd bit rate) ..... you can see such action in the alcorn mcbride digital HD Video machine for example .. which runs win2k (embedded)