Windows-Mobile Directshow: Specifying bitrate/quality of a WMV video capture
- by Landstander
Hi- I'm stumped on this, and I'm really hoping someone could point me in the right direction.
I'm currently capturing video in Windows Mobile and encoding it using the WMV 9 DMO (CLSID_CWMV9EncMediaObject). That all works well enough, but the output video's bitrate is too high, resulting in a video file that's much too large for my needs.
Ultimately, my goal is to mimic the video settings that Microsoft's Camera Capture Dialog outputs in the "messaging" quality mode (64kbps) from my C++ code. Currently, my code's outputting a WMV file with a bitrate of 352kbps.
The only example I could find of specifying the capture bitrate with a WMV9 DMO was this. The idea in that code was basically to use a propertybag to write a bitrate to a property of the DMO.
Update: In windows mobile, the closest codec property I can find that seems to equate to the bitrate is "g_wszWMVCVBRQuality". Microsoft's documentation of this property is extremely confusing to me: It basically seems to say that a higher number equates to a higher quality, but it gives absolutely no explanation of the specifics for each number. When I attempt to set this property to value like "1" via a propertybag for the WMV9 DMO, I run into a -2147467259 (unknown) error.
To summarize: What is the basic strategy to specify the bitrate/quality of a video being captured via directshow (wmv9) on a windows mobile platform?
I've heard (or wondered about) the following methods:
Use the propertybag to change the encoder DMO's property that corresponds to bitrate/quality (currently failing)
Create your own custom transcoder/encoder to specify it. This seems unnecessary since the WMV encoder works well enough- it's just at too high a bitrate.
The VIDEOINFOHEADER has a bitrate property, but I suspect that specifying new settings here will do nothing to alter the actual encoding process since I wouldn't think file attributes would come into play until after the encoding.
Any suggestions?
PS:
I would post specific source code, but at this point it may confuse more than it helps since I'm floundering so much on how to do this. At this point, I'm just trying to validate the general strategy.
THANKS!
