Micro SD card perfromance

[NeilSimpson]

Good morning.

I have been playing 1080p video fromon the iMX53 QSB using the supplied Ubuntu demo OS, and the video plays back very nicely indeed.  The SD card is a Kingston 4GB class 4.  When I build the BSP on my own unbranded 8GB class 10 card it also plays back fine, but I notice on some 'zoom in' parts there is a very slight stuttering.  I wonder if you folks have any idea if this could be to do with a difference in the SD card somehow, or if it's more likely to be processes running on my BSP build which are not there in the other demo card?  Are there any general opinions on whether a faster 'class' card is worthwhile, and whether branding makes much difference?

Thanks!

[WangZening]

The SD card speed is vital for high-bitrate video playback. The video bitrate could be VBR for many HD clips. So, even the video's bitrate is marked as, say, 10Mbps, the peak bitrate could be 20Mbps or even higher. Although we designed buffer queue to smooth the bitrate and decoding speed, it might still has problem if the SD card speed is not fast enough to read in video stream.

When you doubt the SD card is the bottleneck, you can have a speed test of the SD card. The rule-of-thumb is that the average SD card read speed should be 2x~3x of the nominal bitrate of the video clip to guarantee the smooth playback. 

[NeilSimpson]

Bought a transcend 8GB class 6 card and it comfortably outperforms the unbranded class 10 for read and write!