Thanks Ross.
The audio/video are in sync when viewing the actual stream in
QuickTime (haven't tried VLC). Interestingly enough, we are doing
another process which converts the RTSP stream to RTMP (Flash) and we
see a consistent half second sync issue after that process. The
interesting part is that this isn't the same behavior that we see with
the openRTSP recordings.
I hear you regarding capturing to MP4/MOV files. Do you think that
capturing to raw files and then putting them together using another
process would yield better results?
-s
Message: 8
Date: Tue, 19 May 2009 15:52:31 -0700
From: Ross Finlayson <finlay...@live555.com>
Subject: Re: [Live-devel] openRTSP woes
To: LIVE555 Streaming Media - development & use
<live-de...@ns.live555.com>
Message-ID: <f06240804c638e2a78...@[66.80.62.44]>
Content-Type: text/plain; charset="us-ascii" ; format="flowed"
The second issue that we have run into is with audio/video sync.
Right now, at the beginning of many of the recorded files, we are
seeing very fast video with normal speed audio which I think is the
culprit. This lasts for less than a second. (Using the -y flag
seems to help but it throws away audio data making our audio very
bad) Is it possible this occurs until the first keyframe is seen?
We are encoding at full resolution and full framerate from these
cams:
openRTSP -q -f 30 -w 1280 -h 720 -t -Q -b 2000000
rtsp://10.10.10.10/axis-media/media.amp?videocodec=h264&resolution=1280x720&audio=1&duration=0&fps=30&videobitrate=10000&videomaxbitrate=10000&videobitratepriority=framerate&videokeyframeinterval=2&compression=10&color=1&clock=0&date=0&text=0
First, you should make sure that you are seeing properly synced audio
and video when you play the stream directly, using (e.g.) VLC. If
(for whatever reason) you're not getting A/V sync when you play the
stream directly, then you will never be able to get A/V sync when you
record the data into a file.
Second, it's important to realize that the ".mov" (or ".mp4") file
format is badly designed, and is poorly suited for recording live
input streams (like these). One basic problem with the file format
is that it records audio/video data using sample/frame *durations*,
rather than timestamps (or presentation times). This makes it very
difficult to keep audio/video data in sync, if the input data is
synchronized using presentation times, as is the case for incoming
RTP/RTCP data. Because of this, the current implementation of
writing ".mov" or ".mp4" files is - and will likely always remain -
an unreliable hack.
If you want to have any chance of A/V sync working when writing
".mov" or ".mp4" files, then you *must* use the "-y" option. This
may lose a small amount of initial data (until RTCP synchronization
begins), but that's unavoidable.
If you really want to look at the appropriate code for this, then the
class to look at is "QuickTimeFileSync".
--
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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