[Libav-user] Using libavformat for LowLatency Dash

[Simon Brown]

Hi,
If I use ffmpeg to produce -f ldash it takes a long time to sync, and I
need to first produce an h264 output stream and then feed that back into
ffmpeg to pass to the dash encoder.  I have an h264 stream coming in, and I
don't want to re-encode.

So I now want to use code written based on the remuxing example to take the
stream in and output low latency dash.  I have set up a dictionary with all
the options I had from the command line for ffmpeg and all seems to be
working, yet i can't play the stream (the FFmpeg stream does play).

I've compared the two .mpd files and have noticed a few differences, the
most significant of these being:
1) bandwidth:  ffmpeg produces what appears to be a genuine number,
libavformat gets told it's 6Mbps and is a static number despite the
somewhat varying bitrate.
2) in the SegmentTimeline the s and d values are quite different t=unix
time stamp in the libavformat case (1541276893), and seems to be an offset
from 0 in the ffmpeg case (23855872), and d is 12800 in the ffmpeg case and
1080000 in the libavformat case.

Can anyone help with a) getting a bitrate measure from the libav libraries?
b) explaining the s and d values in the mpd file, and what significance
their differences might be causing?

Many thanks,
Simon
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