Image quality for streaming live tv

[buju]

Hi, I have been comparing Tversity and PMS for a while. Unfortunately I could not drop Tversity fully yet as there are still a few items where PMS comes short.
Tversity seems to have a better image quality when streaming live TV and it is also able to stream more RSS video feeds than PMS.
Since I am dealing already with the latter subject within a separate thread, let's focus on the first issue - image quality.

To me it looks very obvious that when using PMS+VLC streaming of live TV is done at a lower PQ (picture quality) than Tversity.
The issue seems to be around pixelation - maybe introduced from transcoding? Actually, I am not even sure if there is any transcoding done, as the streams seem to be in mpeg1 format, anyway.

Anyway, I am seeing this for all streams.

Can anyone pitch in and give an opinon on what can be done to improve the quality of the stream?
I know that this is a VLC issue, and not a PMS one, but hopefully you can help.
Is there any particular VLC setting that I could tweak in order to get better results?

NOTE: I am NOT talking of cases where there are poor network conditions, etc.

Thanks.

[shagrath]

the web transcode bitrate cannot be modified for now (it's 4Mb by default), I plan to add some configuration parameters about this, though

[buju]

Glad to hear that an improvement will be possible from within PMS.
For the time being is there any VLC side tweak possible?

And if you don't mind - when you say transcoding bitrate - are you talking about the bitrate of the stream going out to the PS3?
I did not compare the bitrates on PS3 - Tversity va PMS. But I believe that I recall some high bitrates on Tversity - not sure for what streams though.
I will check and see. I am curious if there is a major difference or not.
I would have thought that it was just a matter of VLC engine not being as able to handle the stream as whatever engine is used in Tversity.

Thanks

[whome]

Maybe TVersity does not always transcode netstreams if recognised them to be PS3 compatible. PS3MS for now always use VLC transcoding. You can simulate PS3MS inner work to output streaming to a mpeg file. PS3MS outputs to \\pipe but it makes no difference here.

vb=video bitrate

Code: Select all

set input=http://www.podtrac.com/pts/redirect.avi/bitcast-a.bitgravity.com/revision3/web/diggnation/0193/diggnation--0193--cockiotron--large.xvid.avi
rem set input=http://videos.theonion.com/onion_video/2009/03/10/4096_TEAMS.flv

set VLC=C:\Program Files\VideoLAN\VLC\vlc.exe
rem set VLC=C:\apps\vlc-0.9.8a\vlc.exe
rem set VLC=C:\apps\vlc-0.8.6-skintest\vlc.exe

"%VLC%" -I dummy %input% :sout=#transcode{vcodec=mp2v,vb=4096,acodec=mp3,ab=128,channels=2}:duplicate{dst=std{access=file,mux=ts,dst="output.mpeg"}}

@rem pause


[buju]

In Tversity you can set the transcoding option. You can set it to: Never, When Need, or Always.
I checked a few channels and they do not work with the transcoding set to OFF.

Now, let's look at a head to head comparison using Orange Sports: rtsp://livewm.orange.fr/live-multicanaux/video

When using PMS:
Audio: MP3 2Ch, 44.1 kHz 128 kbps
Video: MPEG-2 4.1-4.4 Mbps (VBR, I suppose)

When using Tversity:
Audio: MPEG (MPA?) 2Ch, 44.1 kHz 190 kbps
Video: MPEG-1 1.6-4.4 Mbps (definitely VBR)

Tversity produces a clearly better stream, with superior PQ.

[buju]

Whome, any feedback on the above?
As for the code you have shown - how would I use that? And - why would I, if it does not help - if I understood you correctly.
Thanks.

[whome]

VLC batch script I posted is basicly the very same command PS3MS is using internally, opening a VLC writing to \\pipe "file", PS3MS reads pipe and writes to a network outputstream. I am using it to experiment with different VLC commandlines to see what works best. Script saves to a mpeg file for preview comparision. I don't have any definitive answer to say get best IQ, thought not done any extensive testings. I don't have TVersity to debug exact video settings in use.

[buju]

Thanks whome.

shagrath, it'd be great if you got some time to look into this issue.
First of all I don't know why transcoding would be required for large majority of streams out there.
Hopefully you can do away with having to transcode for the majority of the streams.
Then, for those that you will have to transcode - hopefully the solution you're planning (see above) will do well.

I would strongly encourage you to have a look at TVersity and try figuring it out why their streaming quality is better.

I trully believe that your product can become an industry standard. Heck, Sony should pay you for your dev work.
Anyway, thanks and keep us the fab work.

I am looking forward to testing and using the next release.