On 05/13/2010 08:07 AM, Benjamin M. Schwartz wrote: > On 05/13/2010 03:26 AM, James Cameron wrote: >> We discussed this briefly in team meeting this morning ... Record is >> writing an uncompressed stream to SD, before then compressing it in the >> "Save" step once the video recording is stopped. (I could be wrong). >> >> This means that no matter what the size of the buffer memory, if the >> data rate from the camera exceeds the rate at which we can write to SD, >> there will be skips once a recording is long enough to fill the buffer. > ... >> So we determine the data rate by choosing height, width, and frame rate >> from the camera. We determine the maximum rate according to the choice >> of SD media. > > If I understand correctly, Record does compress the video on the fly. > It's the audio that it writes uncompressed to disk for later compression > and muxing. I don't know at what quality it performs audio recording, but > it might be as low as 32 KB/s uncompressed.
I highly doubt that record is sending raw video to the SD device. If it is then its broken and no wonder its skipping. Raw 640x480 RGB at 30 frames a second is 27MiB/s. Even if you use a YUV format with 16bits/pixel and 15 frames a second its still 9MiB/s which exceeds the sustained write rate of a class 6 card. We ship class 2 (2MiB/s). If we can't do theora on the fly then we should be doing MJPEG or HuffYUV (if you wanted a lossless format). Although HuffYUV is still going to be much faster than a Class 2 card. Even MJPEG (roughly /10) is still pushing it. -- Richard A. Smith <[email protected]> One Laptop per Child _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
