[Libav-user] Why is HTTP streaming so slow?

Michael Bradshaw mbradshaw at sorensonmedia.com
Mon May 28 22:05:56 CEST 2012

On Fri, May 25, 2012 at 12:48 PM, Camera Man
<i.like.privacy.too at gmail.com> wrote:
> On 05/24/2012 03:07 PM, Michael Bradshaw wrote:
> Is there a particular reason FFmpeg streams so slowly?
> Speculation: Sounds like it might be a buffering problem: The easy way to
> test it is to time transfers from a nearby machine (localhost or anything
> with <1ms ping time), vs the internet. If  things become disproportionally
> faster (e.g., chrome goes *3 from 4MB/sec to 12MB/sec but ffmpeg goes *50
> from 80KB/sec to 4MB/sec), then this is your problem.
> Browsers (and wget and curl and friends) set the socket buffers to a few
> megabytes. IIRC, ffmpeg leaves tcp connections at the 8KB default. Which
> means, after 8K-16K have been received and not yet processed (which takes
> all of ~5ms in your case), the local kernel tells the remote one "my buffer
> is full, stop sending", and only when this has been processed, it will tell
> the other side "ok, you can resume". Because of how TCP works, this is
> synchronous and inserts delays that depend on the ping time to the server.
> AFAIK, there's no way to set the http/tcp buffer size in ffmpeg; (udp
> connections have the ?buffer_size=xxxx option, but tcp doesn't)

Great, thanks for that input. I'll check the transfer speeds going
through localhost when I get the chance tomorrow. I wouldn't be
surprised if that's it, and I hope it is because it sounds decently



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