mpeg2 transport stream, vlc ffmpeg

[chriskross]

hello everybody... i need your help please

I'm working with a small local tv station and want to feed in our video files in the cable network.

I actually have a working solution, but I'm not really lucky with it, because some cable reveiver (set-top boxes) have problems
when playing my stream. audio video dropouts.

Currently I'm doing the following:
- I have mpeg input files, 720x576, 16:9, 25fps
progressive, interlaced (bff, tff)

I convert them with ffmpeg to mpegts

ffmpeg -y -i $i -flags +ilme -pix_fmt yuv420p -r 25 -s 720x576 -profile:v 4 -bf 2 -b:v 4000k -maxrate:v 5000k -acodec mp2 -ac 2 -ab 128k -ar 48000 -f mpegts $FILE_TMP

output is almost similar to other tv stations

Format                                   : MPEG Video
Format version                           : Version 2
Format profile                           : Main@Main
Format settings, BVOP                    : Yes
Format settings, Matrix                  : Default
Format settings, GOP                     : M=3, N=12
Codec ID                                 : 2
Duration                                 : 27s 879ms
Bit rate mode                            : Variable
Bit rate                                 : 3 101 Kbps
Maximum bit rate                         : 5 000 Kbps
Width                                    : 720 pixels
Height                                   : 576 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 25.000 fps
Standard                                 : PAL
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Interlaced
Scan order                               : Top Field First

for playout i use vlc

cvlc -d --loop --miface eth1 ../playout/$PLAYOUTFILE --sout '#std{access=udp,mux=ts,dst=230.1.0.2:5000}'

bitrate is really low, but setting it to 5 or 6mbit, set-top boxes have problems to display the video. Also I have to set audio bitrate
to 128kbit, a higher value results in dropouts.

I'm a bit confused about that, because other tv stations play with 4-12mbit and 192kbit audio and have no problems.
what I'm doing wrong?
I would appreciate every hints about my issue... maybe other solutions...

thanks for reading

[El Heggunte]

Just a wild guess, but maybe you need to add other parameters to the ffmpeg muxer.

For example:

-mpegts_original_network_id 0x1122

-mpegts_transport_stream_id 0x3344

-mpegts_service_id 0x5566

-mpegts_pmt_start_pid 0x1500

-mpegts_start_pid 0x150

-metadata service_provider="xxxxxxx"

-metadata service_name="xxxxxxxxxx"

Regarding the "playout", perhaps you'll also have to ensure the adequate packet size (188 bytes)
plus a buffer size "big enough".

[chriskross]

thanks for your reply.

my cable network operator told me, the settings are not necessary, because the are rewritten on their system.

where to add the buffer size and packet size?

added -bufsize 1835008 to my ffmpeg line and give it a try.

In vlc i found "mtu" and "ts-csa-pkt" (default 188), is it that what you mean?
mtu is 1500 i guess, but i do not know how to use these values

[El Heggunte]

Well, I simply repeated what is written in the ffmpeg documentation , and since I don't use VLC, I cannot give an answer to your last question.

BTW,

http://www.waveguide.se/?article=creating-dvb-t-compatible-mpeg2-streams-using-ffmpeg

HTH.

[chriskross]

yes maybe bufsize does the trick... I already used it in my about 150 test streams, but didn't recognize any differences with or without this option.
perhaps some set-top-boxes need it.. will watch this the next days.
thanks so far

[El Heggunte]

yes maybe bufsize does the trick... I already used it in my about 150 test streams, but didn't recognize any differences with or without this option.
perhaps some set-top-boxes need it.. will watch this the next days.
thanks so far

You're welcome Or should I say "not at all"?

Seriously though, now I think you should read more carefully the page I indicated in my previous post. Some/many hardware decoders "don't like" open GOPs for example, and ffmpeg really doesn't enforce closed GOPs unless you set B-frames to zero OR disable the scene detection algorithm

Another thing, probably it's a good idea to increase the GOP-size to 25, 30 or 36 frames, so that you'll get a lower average bitrate without a significant loss of quality Last but not least, perhaps ffmbc can give better results than ffmpeg.

Again, hope this helps.

[chriskross]

I already found this article some days ago and played around with gops and buffer...

and ffmpeg really doesn't enforce closed GOPs unless you set B-frames to zero

-bf 0 ?

changing GOP size will change this values i think!?
M=3, N=12
suddenly the M is missing after conversion
to be honest, i hardly unterstand the GOP thing...

@ffmbc
i'll look into it, thx