Date: Mon, 22 Dec 1997 12:09:02 -0500 From: Randall Hopper <rhh@ct.picker.com> To: Petri Helenius <pete@sms.fi> Cc: Amancio Hasty <hasty@rah.star-gate.com>, multimedia@FreeBSD.ORG Subject: Re: MPEG audio/video sync & Re: These mtv video pauses are murder Message-ID: <19971222120902.23203@ct.picker.com> In-Reply-To: <199712220916.LAA22145@silver.sms.fi>; from Petri Helenius on Mon, Dec 22, 1997 at 11:16:29AM %2B0200 References: <19971221222047.08726@ct.picker.com> <199712220329.TAA00402@rah.star-gate.com> <19971221225947.08124@ct.picker.com> <199712220916.LAA22145@silver.sms.fi>
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Petri Helenius: |Randall Hopper writes: | > | > Say, something I've been meaning to ask you and the group. Is there | > something in the MPEG system stream format that you know of which allows | > you to "attach" (or suggest a relation) between a particular point in the | > video and the audio streams. Or is that implicit in the interleaving. | |MPEG system stream contains "PTS"s which stands for "Presentation Time |Stamp". I cannot recall from top of my head at which point the data |should be going at the same time when the PTS hits. It's either the |last or the first byte of the pack and it was supposed to either play |back or enter the decoder at the time of PTS. I've to check the spec. Interesting. Thanks for the info. I'll look this up and see if I can drop these breadcrumbs in mpeg_encode's direction and get it to carry them through for each video frame. |It's possible to address, however doing PTS's is not a perfect way |since some decoders drop or fill in frames to keep the sync. However, |it's much better than no sync at all. Right. That's really all I want. I know mtv or whatever decoder is going to have to skip frames, particularly for slower machines. I just want to be able to give it hints as to where to skip "to". Even if if no frames need to be skipped during decoding, a frame or two now and then might need to be tossed to try and stay in sync with the audio stream. Sounds like PTS is what I was looking for. |I think carrying the timestamps trough the elementary stream phase |might be difficult. Ok. I'll take a look. Thanks. Randall
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