[Icecast] Webm files written without duration in header

Marvin Scholz epirat07 at gmail.com
Wed May 1 20:41:03 UTC 2019

On 1 May 2019, at 22:30, Fred Gleason wrote:

> On Wed, 2019-05-01 at 22:06 +0200, Sytze Visser wrote:
>> The point is that if I can successfully stream mp4 with H.264 and AAC
>> encoding without any issues to icecast, I can then use ffmpeg to
>> turn it into HLS which then solves my iOS support issue. The CPU
>> cost of repackaging MP4 into HLS architecture should be minimal
>> because at the core it’s all H.264. No transcoding! Low CPU objective
>> achieved!
> So all FFMPEG is doing is segmenting the stream and generating the m3u8
> index? Yes, I'd expect that to be quite efficient.

Depending how you segment the stream it can be very efficient as only
remuxing is required in some cases.

>> My question remains
>> If webm/ogv is supported but mp4 not, what are the technical
>> differences
>> in how icecast handles the one and not the other? What does icecast
>> manage/do for supported formats as opposed to unsupported ones?
> It's been a few years since I looked at the source, but IIRC adding
> support for a new codec is pretty simple -- mostly a matter of getting
> it to recognize and emit the correct mimetype(s).

It is not as trivial as that, basically Icecast needs to be able to
properly packetize the format and ideally read metadata from it.

Especially for video it can be even more complex, as ideally Icecast
would ensure to send clients video data starting with a keyframe
if one is in the buffer.

And as I already wrote in my last mail, MP4 is not streamable.

> Of course, you'll also need an ICES client that is capable of
> supporting the desired codec. That may be more challenging than hacking
> Icecast itself.

FFMpeg is already capable to stream nearly any format to Icecast, of
course if it works or not depends a lot on the format as for all
unsupported formats Icecast does no handling whatsoever.

> Cheers!
> |---------------------------------------------------------------------|
> | Frederick F. Gleason, Jr. |             Chief Developer             |
> |                           |             Paravel Systems             |
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