On Thu, 3 Feb 2005, Bene Martin wrote:
I've run into a problem trying to handle Files recorded via DVB with mythtv 0.16 with nuvexport-mpegcut:
* DVB recordings seem to be PES streams, which avidemux2 can't handle. A seperate remultiplexing step to convert to PS stream is needed before cutting.
I don't have a DVB card, but from what I understand it's probably not a PES, but a TS. From the libdvb dvb-mpegtools source README:
"Some information about the different stream types:
1) Elementary stream (ES):
is the stream that contains the actual compressed
audio and video data, like I, P, B-Frames
etc., with respective headers and some
other information.2) Packetized elementary stream (PES):
is composed of Packets containing ES data. The packets have
headers, that specify the respective ES data, like
0x000001E0 for the first video stream. The header also
holds the packet length and stuff like the PTS.3) Program Stream (PS):
mainly contains PES packets with some
additional packets containing some more
information for the decoder, like the SCR,
buffer sizes and mux rates. PSs are used by
DVDs and distributed .vob files.4) Transport Stream (TS):
is composed of packets that all have the
same size (188bytes). They all start with 0x47.
The packets are identified by their PID.
Some of them contain audio and video data
in the form of PES packets which are spread
over many packets of size 188 bytes. Other
packets contain sections which contain various
things like the PMT, the PAT or videotext
data. A TS is meant for transporting data
over networks."The stream that comes off the air is a TS, and the DVB card probably just sends that down (although it might do PID filtering on the way). The dvb-mpegtools includes a number of utilities to encapsulate or strip off these layers... probably an invokation of 'ts2ps' from that toolkit is in your future... :)
Just as an aside, I'd like to say that this information from the dvb-mpegtools finally confirms my suspicions on why demuxing a stream into it's audio and video to remux them is a very bad idea. Those are ES (level 1 above), and the PTS (Presentation Time Stamp) isn't included until it's a PES (level 2). That's why some videos lose sync when remuxed in that way but others don't. If the PTS offset between the video and audio changes throughout the stream, demuxing to .m2v and .m2a will break sync. If the PTS offset stays constant, it'll work fine (maybe with at static offset like 'mplex -O 66ms...' or something).
-Cory
************************************************************************* * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * *************************************************************************
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