[FFmpeg-devel] Transcoding HLS segments post-hoc

Stefano Sabatini stefasab at gmail.com
Fri Aug 16 12:55:21 CEST 2013

On date Thursday 2013-08-15 17:17:21 +1000, Ray Hilton encoded:
> Hi,
> Sorry, this isn't directly to do with internal dev, but the consulting
> page recommended emailing this list if I wasn't sure who to contact.
> Rather than individually emailing everyone with more or less the same
> thing, i'll post here and hopefully someone will be able to help!  We
> might be able to get money together to pay for consulting if the
> solution to this problem is some custom ffmpeg work.
> Bit of background: we are providing a streaming live/on-demand
> solution to the community radio sector in Australia.  We're trying to
> find a way to provide HLS streaming from live, continuous audio in a
> variety of bitrates and codecs and ideally take advantage of adaptive
> streaming (i.e. segments are in sync).

> First, is this possible:  I am segmenting audio from a live stream
> using AAC at 128k.  I send those segments to our cluster and they
> transcode them into various other bitrates/formats using things like
> neroaac (better low bitrate quality) and lame.  This works, but it
> introduces gaps between the segments.  This is an ideal solution as
> the origin (radio stations) upload just the highest quality format and
> we distribute the workload to do the rest.  We can also use the same
> implementation for "live" as well as "on demand".  What is ffmpeg
> doing internally when segmenting to avoid the gaps?

Did you have a look at the segment and hls muxer? You can use ffmpeg
to transcode the files, using the internal AAC muxer or the various
supported wrappers. You can add an offset to files, but at the moment
this implies transcoding and thus doesn't look like a viable solution.

> The second option is to use small machines in the studio to transcode
> from audio device to multiple nitrates/formats.  Ideally, for adaptive
> streaming, we want these segments to be in sync - is that possible?
FFmpeg = Free & Fundamental Mastodontic Patchable Eager Genius

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