MPEG2 Transport Stream vs Program Stream

[GollyJer]

There seems to be some confusion as to what these are. Hopefully I can help, and others will jump in if needed.

There's more to it than what I'm about to outline, but I'll point out the more useful things and let you dig deeper by reading this article.

• An MPEG-2 Program Stream (.mpg files in Sage) contains one, and only one, content channel. I beleive all SD recordings are natively program streams.
• An MPEG-2 Transport Stream (.ts files in Sage) can contain one or more content channels. I believe most, if not all, HD recordings are natively transport streams.

HD recordings are streamed from the content providers as .ts files. If channel 18 has 4 subchannels: 18-1, 18-2, 18-3, 18-4 and you only record 18-3, the .ts file still contains the information for all four channels.

The setting in the Sage.properties file that controls whether or not Sage records to .ts or .mpg files is:
mmc/encode_digital_tv_as_program_stream
By default it is set to true, and I believe with it on Sage is "snipping" 18-3 out of the .ts file and creating a single content program stream. The benefit is smaller file sizes.

If you change the setting to false, the recorded file with be a .ts and unchanged from the format it was sent by the content provider (cable/satellite). This will result in bigger files but no extra processing has to be done.

I came to Sage from BeyondTV. BTV records to .ts by default and has a feature called "StreamSnip" that let's the user create a Program Stream file on demand, or they can set the machine up to process a file in it's down time.

[camus]

I don't see how this would make any difference for stuttering on playback of a recorded file. Maybe for Live TV, but even then I am not sure.

[ozfiles]

Well I've learnt something today, thanks GollyJer.

[stanger89]

Originally Posted by GollyJer

There seems to be some confusion as to what these are. Hopefully I can help, and others will jump in if needed.

There's more to it than than what I'm about to outline, but I'll point out the more useful things and let you dig deeper by reading this article.

• An MPEG-2 Program Stream (.mpg files in Sage) contains one, and only one, content channel. I beleive all SD recordings are natively program streams.

If you're talking SD recordings, as in analog recordings, then yes the PVR cards all record to a PS format.

• An MPEG-2 Transport Stream (.ts files in Sage) can contain one or more content channels. I believe most, if not all, HD recordings are natively transport streams.

All digital broadcasts I'm aware of (OTA, Cable, Sat) are TS format, regardless of HD or SD. The complexity comes because many digital tuners will strip substreams and save the content to a PS format.

HD recordings are streamed from the content providers as .ts files. If channel 18 has 4 subchannels: 18-1, 18-2, 18-3, 18-4 and you only record 18-3, the .ts file still contains the information for all four channels.

Depends on the application, I'd say at this point that most digital recording products strip out "unwanted" subchannels, so while true that the broadcast may have many subchannels, the recording will only have the one you want. This is the way Sage works.

The setting in the Sage.properties file that controls whether or not Sage records to .ts or .mpg files is:
mmc/encode_digital_tv_as_program_stream
By default it is set to true, and I believe with it on Sage is "snipping" 18-3 out of the .ts file and creating a single content program stream. The benefit is smaller file sizes.

As far as I know, Sage strips unwanted subchannels regardless of the setting of that property. I think there's a different property that enables/disables the recording of "raw" tranport streams, but I don't remember what it is.

If you change the setting to false, the recorded file with be a .ts and unchanged from the format it was sent by the content provider (cable/satellite). This will result in bigger files but no extra processing has to be done.

Like I said, Sage strips subchannels regardless of the setting of that property.

[GollyJer]

Originally Posted by stanger89

As far as I know, Sage strips unwanted subchannels regardless of the setting of that property. I think there's a different property that enables/disables the recording of "raw" tranport streams, but I don't remember what it is.

Interesting, why have the option to leave it as a Transport Stream if it's a single content Program Stream anyway? Maybe for potential use in other programs that don't support Program Stream files? I doubt there are many that don't though.

It's also interesting that Sage can do this on the fly and BeyondTV needs idle processor time to do the stripping.

[jkohn]

I think the only difference between TS and PS in Sage is that the PS files have any null packets stripped out. This would explain why PS files tend to be just a little bit smaller.

I think it's also worth noting that the way Sage strips the extra streams from TS files results in a TS that some programs won't be able to read if the orginal TS had multiple streams in it. I think this is because the meta data in the TS still references the streams that Sage stripped out. For instance, TheaterTek chokes on Sage TS files, and depending on which filters are the default on your system other direct-show based players may also have problems with them.

[GKusnick]

6.1 has some TS fixes that 6.0 doesn't have, so if non-compliant TS files are a problem for you, you should consider trying the beta (if you haven't already) and reporting any remaining compliance issues you find. Beta is your chance to get these things fixed quickly.

[jkohn]

Originally Posted by GKusnick

6.1 has some TS fixes that 6.0 doesn't have, so if non-compliant TS files are a problem for you, you should consider trying the beta (if you haven't already) and reporting any remaining compliance issues you find. Beta is your chance to get these things fixed quickly.

Interesting, in the RC thread there seemed to be a lot of complaints about the performance on HD recordings so I've steered clear of 6.1 so far.

[flavius]

Well, TS fixes - and some new bugs. If you are using the MVP, I would not upgrade.