Hi! Logitech HD Pro Webcam C910 supports 2592x1944 at 10 FPS MJPEG stream. This is really great but the problem is that libv4l decoding of MJPEG is too slow for real-time on the fly decoding at this framerate. I use 2.6.36-rc6-amd64 and Intel(R) Core(TM)2 Quad CPU Q9400 @ 2.66GHz and 0.8.1 v4l-utils.
For example, with libv4l decoding of one pixel of MJPEG to BGR24 takes around 0.025 microseconds on my machine. This is nothing important with for example 640x480 resolution, it takes around 7680 microseconds, that is 8 milliseconds. But with 2592x1944 this becomes around 125 milliseconds. So it is impossible to decode stream on the fly in real-time with 10 FPS. In comparison YUYV decoding takes 0.005 microseconds per pixel on average. Those measurements per pixel (both for MJPEG and YUYV) are quite consistent even for different framerates and frame sizes. So maybe there is some room for improvement here? For example by using ffmpeg MJPEG decoder instead of tinyjpeg? They argue (not really kindly) that it has better performance: https://roundup.ffmpeg.org/issue1816 Has anybody tried to improve MJPEG support in libv4l? With newer cameras this becomes important. And by the way, it would be useful to increase those hardcoded limits in ib/libv4lconvert/tinyjpeg-internal.h to for example: #define JPEG_MAX_WIDTH 4096 #define JPEG_MAX_HEIGHT 2048 Now we have affordable cameras which have bigger frame sizes than those currently hardcoded. ;-) Mitar -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
