[vdr] clarification request: vdr file format?

Udo Richter udo_richter at gmx.de
Wed Aug 24 18:41:25 CEST 2005


jik jikman wrote:
> Some sites say it is pva format, some other say it is pes format and
> other say it is ts format without pat/pmt tables.
> 
> What is vdr file format at last? and why we can't record directly in
> mpg ( mpeg ps ) format as we can do in windows?

Some clarifications about terms AFAIK:

Elementary Stream (ES):
Video stream, audio stream or similar data stream.

Packetized Elementary Stream (PES):
ES cut into a sequence of packets. Since all PES packets of one ES share
one stream id, its possible to mix PES packets of several ES streams
into one PES stream. PES also adds information for time synchronization
of the streams.

Transport Stream (TS):
Mainly used for live streams. Another packet stream that packs several
PES streams, each containing only one ES stream, into small packets for
transport. The streams are separated by the packet identifier (PID). TS
also adds data packets describing the contents of the stream.

Program Stream (PS):
The classic mpeg2 video file format. PS packs several PES packets of
different ES streams into 'packs'. Also, PS has info headers describing
the contents of the PS.


PES is not meant to be a file format, its just an internal stream
format. PES or similar formats are widely used by PVRs because data of
TS streams can easily be extracted into PES streams. However, PES as
file format has several disadvantages:

- No content information headers, streams may appear or disappear at any
time. No way to tell exactly whats in it without scanning the whole file.

- Strange A/V syncing, like audio starting a second earlier than video,
or audio and video not having the same length.

- Discontinuities. There may be gaps of several minutes in video and
audio data (cut out). No way to tell how long a video is without
scanning the whole file.


Converting from PES to a well-formatted PS is a tough job, thats why
there are special programs doing that job. Directly recording into PS
wont make it easier.

Cheers,

Udo



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