On 3/23/18 10:57 AM, vdi...@akamai.com wrote:
> From: Vishwanath Dixit <vdi...@akamai.com>
>
> availability time of Nth segment = availabilityStartTime + (N*segment
> duration) - availabilityTimeOffset.
> This field helps to reduce the latency by about a segment duration in
> streaming mode.
> ---
> libavformat/dashenc.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/dashenc.c b/libavformat/dashenc.c
> index b62cb3e..d20bdba 100644
> --- a/libavformat/dashenc.c
> +++ b/libavformat/dashenc.c
> @@ -85,6 +85,7 @@ typedef struct OutputStream {
> char filename[1024];
> char full_path[1024];
> char temp_path[1024];
> + int64_t chunk_duration;
Remove this variable chunk_duration, and instead create a variable directly for
availabilityTimeOffset.
> } OutputStream;
>
> typedef struct DASHContext {
> @@ -343,8 +344,12 @@ static void output_segment_list(OutputStream *os,
> AVIOContext *out, AVFormatCont
> if (c->use_template) {
> int timescale = c->use_timeline ? os->ctx->streams[0]->time_base.den
> : AV_TIME_BASE;
> avio_printf(out, "\t\t\t\t<SegmentTemplate timescale=\"%d\" ",
> timescale);
> - if (!c->use_timeline)
> + if (!c->use_timeline) {
> avio_printf(out, "duration=\"%d\" ", c->seg_duration);
> + if (c->streaming && os->chunk_duration)
> + avio_printf(out, "availabilityTimeOffset=\"%.3f\" ",
> + ((double) c->seg_duration - os->chunk_duration)
> / AV_TIME_BASE);
> + }
> avio_printf(out, "initialization=\"%s\" media=\"%s\"
> startNumber=\"%d\">\n", c->init_seg_name, c->media_seg_name, c->use_timeline
> ? start_number : 1);
> if (c->use_timeline) {
> int64_t cur_time = 0;
> @@ -1283,6 +1288,10 @@ static int dash_write_packet(AVFormatContext *s,
> AVPacket *pkt)
> format_date_now(c->availability_start_time,
> sizeof(c->availability_start_time));
>
> + if (!os->chunk_duration && pkt->duration)
> + os->chunk_duration = av_rescale_q(pkt->duration, st->time_base,
> + AV_TIME_BASE_Q);
Don’t use the term ‘chunk_duration’ here, as it is not clearly conceptualized
in this file.
Instead use the term ‘frame_duration’(local variable) to avoid confusion.
> +
> if (c->use_template && !c->use_timeline) {
> elapsed_duration = pkt->pts - os->first_pts;
> seg_end_duration = (int64_t) os->segment_index * c->seg_duration;
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