[FFmpeg-devel] [PATCH v2 5/5] avformat/hls: add http_multiple option

[Anssi Hannula]

Hi!

Aman Gupta kirjoitti 2017-12-13 02:35:
> From: Aman Gupta <aman at tmm1.net>
> 
> This improves network throughput of the hls demuxer by avoiding
> the latency introduced by downloading segments one at a time.
> 
> The problem is particularly noticable over high-latency network
> connections: for instance, if RTT is 250ms, there will a 250ms idle
> period between when one segment response is read and the next one
> starts.
> 
> The obvious solution to this is to use HTTP pipelining, where a
> second request can be sent (on the persistent http/1.1 connection)
> before the first response is fully read. Unfortunately the way the
> http protocol is implemented in avformat makes implementing pipleining
> very complex.
> 
> Instead, this commit simulates pipelining using two separate persistent
> http connections. This has the advantage of working independently of
> the http_persistent option, and can be used with http/1.0 servers as
> well. The pair of connections is swapped every time a new segment 
> starts
> downloading, and a request for the next segment is sent on the 
> secondary
> connection right away. This means the second response will be ready and
> waiting by the time the current response is fully read.

Thanks, seems like an OK idea and the code seems straight-forward.

Why is this a defaults-to-disabled option, instead of defaulting to 
enabled or just not having an option at all?
I guess there may be a good reason, but I'd like to hear your thoughts 
on that.

> ---
>  doc/demuxers.texi |  3 +++
>  libavformat/hls.c | 51 
> ++++++++++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 51 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/demuxers.texi b/doc/demuxers.texi
> index 18ff7101ac..f2181fbb93 100644
> --- a/doc/demuxers.texi
> +++ b/doc/demuxers.texi
> @@ -319,6 +319,9 @@ Default value is 1000.
> 
>  @item http_persistent
>  Use persistent HTTP connections. Applicable only for HTTP streams.
> +
> + at item http_multiple
> +Use multiple HTTP connections for downloading HTTP segments.
>  @end table
> 
>  @section image2
> diff --git a/libavformat/hls.c b/libavformat/hls.c
> index f75c8f5eaa..487fa9a82f 100644
> --- a/libavformat/hls.c
> +++ b/libavformat/hls.c
[...]
> @@ -1426,11 +1440,20 @@ reload:
>          if (ret)
>              return ret;
> 
> -        ret = open_input(c, v, seg, &v->input);
> +        if (c->http_multiple && v->input_next_requested) {
> +            AVIOContext *tmp = v->input;
> +            v->input = v->input_next;
> +            v->input_next = tmp;

Use FFSWAP().

[...]

-- 
Anssi Hannula