I have a logitech c920 webcam that presents an encoded h264 capture pin (subtype: MEDIASUBTYPE_H264).
The h264 pin supports the following resolutions:
FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 640x480 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 160x90 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 160x120 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 176x144 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 320x180 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 320x240 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 352x288 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 432x240 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 640x360 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 800x448 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 800x600 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 864x480 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 960x720 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 1024x576 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 1280x720 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 1600x896 @ 30 fps FORMAT_VideoInfo - subtype: MEDIASUBTYPE_H264 1920x1080 @ 30 fps
In my testing it always uses 3 Mbits regardless of the selected resolution. It is a bit too much, especially for the lower resolutions.
Any idea on how to programatically select the desired bitrate using directshow? Or maybe other API ?
From the Logitech support answer it follows that the encoding is 80/20 HW/SW and the bitrate (and GOP) cannot be controlled. However their bundled software obviously does that. Other than that, after some limit, there is a decrease in the bit rate, though it occurs at really low resolution/fps combinations:
Required bandwidth for size: ( 1920 , 1080 ) @ 30 is 2.81771 Mbit
Required bandwidth for size: ( 1920 , 1080 ) @ 25 is 2.81672 Mbit
Required bandwidth for size: ( 1920 , 1080 ) @ 20 is 2.82701 Mbit
Required bandwidth for size: ( 1920 , 1080 ) @ 15 is 2.83327 Mbit
Required bandwidth for size: ( 1920 , 1080 ) @ 10 is 2.83594 Mbit
Required bandwidth for size: ( 1920 , 1080 ) @ 5 is 2.8431 Mbit
Required bandwidth for size: ( 1280 , 720 ) @ 30 is 2.82013 Mbit
Required bandwidth for size: ( 1280 , 720 ) @ 25 is 2.82436 Mbit
Required bandwidth for size: ( 1280 , 720 ) @ 20 is 2.83217 Mbit
Required bandwidth for size: ( 1280 , 720 ) @ 15 is 2.83696 Mbit
Required bandwidth for size: ( 1280 , 720 ) @ 10 is 2.83721 Mbit
Required bandwidth for size: ( 1280 , 720 ) @ 5 is 2.45272 Mbit
Required bandwidth for size: ( 864 , 480 ) @ 30 is 2.82089 Mbit
Required bandwidth for size: ( 864 , 480 ) @ 25 is 2.82313 Mbit
Required bandwidth for size: ( 864 , 480 ) @ 20 is 2.83131 Mbit
Required bandwidth for size: ( 864 , 480 ) @ 15 is 2.83343 Mbit
Required bandwidth for size: ( 864 , 480 ) @ 10 is 2.79526 Mbit
Required bandwidth for size: ( 864 , 480 ) @ 5 is 1.15564 Mbit
Required bandwidth for size: ( 320 , 180 ) @ 30 is 1.90123 Mbit
Required bandwidth for size: ( 320 , 180 ) @ 25 is 1.89367 Mbit
Required bandwidth for size: ( 320 , 180 ) @ 20 is 1.26006 Mbit
Required bandwidth for size: ( 320 , 180 ) @ 15 is 0.957935 Mbit
Required bandwidth for size: ( 320 , 180 ) @ 10 is 0.637158 Mbit
Required bandwidth for size: ( 320 , 180 ) @ 5 is 0.328456 Mbit
If you came up with the solution, please, share. Thanks!