mp4.CreateMp4Demuxer: support io.Reader

[3052]

currently only io.ReadSeeker is supported:

https://pkg.go.dev/github.com/yapingcat/gomedia/go-mp4#CreateMp4Demuxer

this is a big problem, as it wont work with HTTP:

https://pkg.go.dev/net/http#Response.Body

this is OK for SegmentTemplate but SegmentBase is a single segment.

[3052]

maybe workaround:
https://github.com/yapingcat/gomedia/blob/main/go-mp4/sidx-box.go
https://gpac.io/2012/02/01/dash-support/

[yapingcat]

seek interface is necessary.
if dash stream is SegmentBase mode, you may get init range and index range. you need to seek to the range to get moov box and sidx box.
http support range request ,which means seek operation for http

for gomedia, seek is used for two purposes.

1. get current offset
2. skip some bytes to goto next box