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Syberkitten
Known Participant
July 30, 2012
Question

Time misalignment on PHDS streams, when seeking forward / back on an OSMF player with subtitles

  • July 30, 2012
  • 1 reply
  • 1772 views

We are using PHDS streams with an OSMF based player.

all streams that are received via RTMP have no problem

with our player in regarding to showing the subtitles (closed captions)

in sync.

yet when we get the stream via PHDS it seems that once in

a seek or two, the captions (subtitles) shift ahead for about 0.5-1 secs.

and as mentioned another seek can fix it or leave it out of sync.

our conclusion is that it has to do with the FMS serving the

stream which somehow deviates the current time of the stream.

ps: when getting the stream for the same video via RTMP

via the same player - the subtitles are OK, the problem is only PHDS

oriented.

any ideas?

thanks.

This topic has been closed for replies.

1 reply

A
Adobe Employee
amit_kr
Adobe Employee
July 30, 2012

Can you tell me which FMS build you are using and what file you are using? Especially codec details and how closed captioning data is present in the file, is it present in the Video data or as a separate track in Data messages.

Does HDS unencrypted plays fine with closed captions?

I need this information to understand your workflow clearly which can help me to diagnose the problem better.

S
SyberkittenAuthor
Known Participant
July 31, 2012

we are using fms build 4.5.2

the captions are loaded as an external file (srt) and digested via our player.

the player uses the currentTime property of the MediaPlayer (osmf) to put

the subtitles on spot and on time.

we tried both unencrypted HDS and PHDS, with same results,

which means a little loss of sync on and off, its not related to

any specific location in the movie, same location can work

well and then not.

rtmp is always in sync btw for the same videos.

video encoding details (media info) :

General

Format                           : MPEG-4

Format profile                   : Base Media

Codec ID                         : isom

File size                        : 618 MiB

Duration                         : 2h 20mn

Overall bit rate                 : 614 Kbps

Writing application              : Lavf53.32.100

Video

Format                           : AVC

Format/Info                      : Advanced Video Codec

Format profile                   : Main@L3.1

Format settings, CABAC           : Yes

Format settings, ReFrames        : 4 frames

Codec ID                         : avc1

Codec ID/Info                    : Advanced Video Coding

Duration                         : 2h 20mn

Bit rate mode                    : Variable

Bit rate                         : 512 Kbps

Width                            : 512 pixels

Height                           : 288 pixels

Display aspect ratio             : 16/9

Frame rate mode                  : Variable

Frame rate                       : 25.000 fps

Resolution                       : 24 bits

Colorimetry                      : 4:2:0

Scan type                        : Progressive

Bits/(Pixel*Frame)               : 0.139

Stream size                      : 515 MiB (83%)

Writing library                  : x264 core 124 r2197 69a0443

Encoding settings                : cabac=1 / ref=4 / deblock=1:0:0 / analyse=0x1:0x111 / me=hex / subme=6 / psy=0 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=12 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=0 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc=2pass / mbtree=0 / bitrate=512 / ratetol=1.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / cplxblur=20.0 / qblur=0.5 / ip_ratio=1.40 / pb_ratio=1.30 / aq=1:1.00

Audio

Format                           : AAC

Format/Info                      : Advanced Audio Codec

Format version                   : Version 4

Format profile                   : LC

Format settings, SBR             : No

Codec ID                         : 40

Duration                         : 2h 20mn

Bit rate mode                    : Constant

Bit rate                         : 96.0 Kbps

Channel(s)                       : 2 channels

Channel positions                : L R

Sampling rate                    : 48.0 KHz

Resolution                       : 16 bits

Stream size                      : 96.7 MiB (16%)

let me know if anything else might help you

help me ...

A
Adobe Employee
amit_kr
Adobe Employee
July 31, 2012

This is expected.

In case of RTMP you are not observing this because RTMP seek is fast as the server sends some data immediately when we seek irrespective of the keyframe and the player starts playing it so it is in sync.

But in case of HDS we have fragments which are downloaded by the player and it has keyframes in it which can be positioned anywhere in the fragment. So, when you seek you get the current time but this might not be same with the time when the player actually starts playing the fragment as it looks for the keyframe. So, sometimes it can be the case that it got the keyframe immediately when it seeked but tsometimes not.

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