Billing from FMS access logs

No known issue here as those are some of the more scrutinized area of FMS.  Most major FMS partners do just what you're doing there to bill, so those numbers have been vetted more than a few times.  Some things to consider

1.  sc-stream-bytes is really what you want if you're billing on content, because that's what the customer is seeing.  sc-bytes is that plus control traffic, rtmp overhead, etc - consequently it's your choice but if we're talking pure content most use this as they may/may not consider the RTMP overhead part of their load here

2.  TCP dump is going to have even more overhead because you're accounting for TCP/IP overhead on stream and that's something that FMS doesn't account for in either sc-stream-bytes or sc-bytes.  Realistically it can't as it's obfuscated from that TCP/IP does at that layer (for example how does it want to track a TCP retransmit)

3.  Simple play-through vs seek/buffering.  Since FMS can seek, or buffer play for some space of data unviewed for baseline billing tests you'll want to make sure it's a simple play from beginning to end as well to set your metrics.  If the customer is seeking, pausing and then closing, etc then this number will also be inaccurate.

Hope that helps,

Asa