Originally Posted by
DiGiCiDAL 
How are you approaching the media on the NAS? By that I mean are you transcoding in this process. Depending on the .avi it may not be supported for the embedded player at the specifications of the source media and thus require transcoding... since the processor (I believe that unit has a 1.6GHz ARM in it) isn't powerful enough to handle transcoding of pretty much anything (other than maybe 320X180 or so) it's pretty limited in it's streaming capability.
What you can do however (and what I do at home) is simply map shares on the client machine and then access them directly through your preferred media client (WMC, Plex, XBMC, etc...) although this maybe still limited by overall bandwidth (if the bitrate is too high for the throughput). For example, my current server connects to my GbE switch and has an average throughput of somewhere between 40MB/sec and 89MB/sec... so I can stream anything to one client, and most HD content to two clients, but if three are active, or if I'm doing transfers or something else on the server then I can only reliably serve SD content to the three clients and even well-compressed 720p content is "iffy".
My current server is also much, much more powerful than this NAS (or any synology NAS for that matter). I'm running a Core i3 3220 on a H77 ITX motherboard - so I've got somewhere around 10X the processing power, and the OS (Fedora), server software (Amahi), and cache for the array are all handled by a 64GB SSD and 8GB of RAM.
Try this for troubleshooting:
Find a good test .avi on the server. Make a local copy of it. Open the remote file natively. Open the local file natively. Open the local file in the browser. Open the remote file in the browser.
If neither open in the browser - it's a plugin, codec, or other file-level issue.
If only the local copies work - it's a bandwidth issue or a transcoding issue.
If it's the second case - use handbrake or whatever transcoder you prefer and transcode the file into a 320X240 or something else very small, also try transcoding it a second time into a different format (preferrably something like .mp4 or .mkv) at the same resolution.
If the same container (.avi) but a smaller size works - it's because of a transcoding error/issue most likely it takes too much CPU power on the NAS to process adequately.
If a different container but the same size works - it's probably a problem with codec registration for that browser/client - or the bitrate is exceeding the network throughput of the device.
Beyond that.... I'm not sure what to suggest, but if anything occurs to me I'll post it here.
