Viewing 1 to 4 (4 Total)
HLS first chunk start time

imran.arshad@icflix.com

Total Posts:
Joined: May 29, 2015

Hello!
We've noticed that first HLS chunk has start offset = 10. I.e. from the ateam example:


ffprobe version 2.8.2 Copyright (c) 2007-2015 the FFmpeg developers
built with Apple LLVM version 7.0.0 (clang-700.1.76)
configuration: --prefix=/usr/local/Cellar/ffmpeg/2.8.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-opencl --enable-libx264 --enable-libmp3lame --enable-libvo-aacenc --enable-libxvid --enable-libfreetype --enable-libvorbis --enable-libvpx --enable-libfaac --enable-libass --enable-ffplay --enable-libfdk-aac --enable-libopus --enable-libquvi --enable-libx265 --enable-nonfree --enable-vda
libavutil 54. 31.100 / 54. 31.100
libavcodec 56. 60.100 / 56. 60.100
libavformat 56. 40.101 / 56. 40.101
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 40.101 / 5. 40.101
libavresample 2. 1. 0 / 2. 1. 0
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 2.101 / 1. 2.101
libpostproc 53. 3.100 / 53. 3.100
Input #0, mpegts, from 'http://demo.unified-streaming.com/video/ateam/ateam.ism/ateam-audio=128000-video=400000-1.ts':
Duration: 00:00:08.01,start: 10.000000, bitrate: 499 kb/s
Program 16727
Stream #0:00x22: Audio: aac (LC) (15000 / 0x000F), 44100 Hz, stereo, fltp, 5 kb/s
Stream #0:10x21: Video: h264 (Constrained Baseline) (27000 / 0x001B), yuv420p, 220x124 SAR 248:187 DAR 40:17, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
Stream #0:20x23: Data: timed_id3 (ID3 / 0x20334449)
Unsupported codec with id 1414087731 for input stream 2


Some of the players honor chunk-related start offset, which breaks external subtitles.
Is there particular reason for hardcoded start offset?
Is there a way to configure the start offset and set it to 0 for the first chunk?

Thanks!

Tags:
Posted on January 24, 2016 at 8:14 AM

will@unified-streaming.com

will@unified-streaming.com
Total Posts:
Joined: August 04, 2015

Re: HLS first chunk start time

Hi Imran,

Apple uses an initial 10 second offset and that is why we use it as well.

How to synchronize, please see:http://tools.ietf.org/html/draft-pantos-http-live-streaming-18...

--

In order to synchronize timestamps between audio/video and subtitles,
a X-TIMESTAMP-MAP metadata header SHOULD be added to each WebVTT
header. This header maps WebVTT cue timestamps to MPEG-2 (PES)
timestamps in other Renditions of the Variant Stream. Its format is:

X-TIMESTAMP-MAP=LOCAL:,MPEGTS:
e.g. X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
--

The above X-TIMESTAMP-MAP maps zero 0 (from the subtitles) to 10 seconds (MPEGTS:900000) audio/video time.

Kind regards,

Will.

Posted on January 26, 2016 at 10:32 AM

imran.arshad@icflix.com

Total Posts:
Joined: May 29, 2015

Re: HLS first chunk start time

Hi!
Do you have any option to configure the initial offset?

Posted on January 26, 2016 at 11:47 AM

will@unified-streaming.com

will@unified-streaming.com
Total Posts:
Joined: August 04, 2015

Re: HLS first chunk start time

See above, this is part of the HLS specification and is therefore not configurable.

Kind regards,

Will.

Posted on January 26, 2016 at 11:49 AM