BUG- need the bitrate remain resonable

[phomlish]

Guys,

I've posted a few times about this, and still have not resolved the issues.

I am working with Carnegie Mellon with their End System Multicast team (http://esm.cs.cmu.edu/), and they have pretty much given up on videolan vlc. However, I would really like them to use it instead of micro$oft media encoder.

We NEED to define a bitrate and have vlc keep the stream under the defined settings. 128K video, and 96K audio would be a nice start.

Why are we having so many troubles getting this to work? We keep seeing streams > 500K with these settings, which just isn't going to work.

Thanks,
Paul

here is the command line I'm using
vlc test.m3u \
--loop \
--rc-host 10.11.1.92:70123 \
--extraintf ncurses \
-vvv --sout \
'#transcode{vcodec=mp4v,acodec=mpga,vb=128,ab=96}:standard{access=udp,mux=ts,url=10.11.1.52:23450}'

[vlcuser]

Guys,

I've posted a few times about this, and still have not resolved the issues.

I am working with Carnegie Mellon with their End System Multicast team (http://esm.cs.cmu.edu/), and they have pretty much given up on videolan vlc. However, I would really like them to use it instead of micro$oft media encoder.

We NEED to define a bitrate and have vlc keep the stream under the defined settings. 128K video, and 96K audio would be a nice start.

Why are we having so many troubles getting this to work? We keep seeing streams > 500K with these settings, which just isn't going to work.

Thanks,
Paul

here is the command line I'm using
vlc test.m3u \
--loop \
--rc-host 10.11.1.92:70123 \
--extraintf ncurses \
-vvv --sout \
'#transcode{vcodec=mp4v,acodec=mpga,vb=128,ab=96}:standard{access=udp,mux=ts,url=10.11.1.52:23450}'

I 've the same problem... I think this is because ffmpeg using a variable bitrate codec.

[The DJ]

one: if the fps + framesize + highest compression possible with selected codec, then the bitrate setting will be "as close as possible". Ergo the vb= setting is a "target" rate and not at all absolute. This is how ffmpeg works.

Try lowering other quality settings as well. Unfortunately i have little experience with transcoding myself.

two: indeed the coding is VBR. Doing proper CBR requires multiple passes by the decoder (and with mpeg4 and h264 even then it's just an approximation), which VLC cannot do on the fly.

[xtophe]

And if you llok at the option of ffmpeg ( vlc -p ffmpeg --advanced --help-verbose) you'll see that there are loads of options and some of them can help you to have a stream less variable in bitrate.

[phomlish]

I'm so not an expert here. Could someone please help me with some hints on what might help? I need to take this barrel of snakes and get them layed out nice and straight for me.

is this a good one?
--sout-ffmpeg-strict-rc

I hear this voice, and it keeps getting louder, saying:

"Now bow down and admit, thy God is Gates!"

Please, don't let it be!

Paul

[klaberte]

I'm so not an expert here. Could someone please help me with some hints on what might help? I need to take this barrel of snakes and get them layed out nice and straight for me.

is this a good one?
--sout-ffmpeg-strict-rc

I hear this voice, and it keeps getting louder, saying:

"Now bow down and admit, thy God is Gates!"

Please, don't let it be!

Paul

Yes, that's the one. Doing this will keep ffmpeg from allowing the the instantaneous bit rate from wandering too far from the VBR average.

Ken

[rahulsharma]

Hello folks,

We are also facing certain problems related to fluctuating bitrates by VLC. I would like to know in particular is VideoLan developers have taken a note of this allready? Can anyone lead me to the ticket / track No. where the bug related to such fluctuations is accepted.

looking forward for a prompt reply.

Regards
Rahul Sharma

[DJ]

This is not a bug it's a feature set, this is how most encoders work. If you give a fixed bit rate the encoder will try to maintain a CBR (Constant bit rate) with variable compression if you tell it to use ABR (Average bit rate) the value you set for the average, with optional Maximum and minimum settings is what it will do. If you tell it you want true VBR (Variable bit rate) where the bit rate is based on the complexity of the source and the compression is based on the average bit rate required by the source then that's what the encoder will do. I guess it all boils down to your ability to know WHAT YOU WANT and express this in relation to your source as there is no one do all or all good settings.

Most people these days believe VBR gives a better over all picture based on an ABR setting. So in complex scenes the bit rate will clime and in almost static scenes the bit rate will fall. Compression ratio then becomes a function of the ABR setting. But this can also be changed.

[The DJ]

Also, CBR is very difficult, especially with MPEG-4 and newer codecs. The only way to do it, is usually to define a lowever strict CBR (which won't be strict), and then add stuffing in the "file/stream format". Somewhat a lousy approach and wasting bandwith.

Note that VLC is not a "one shot" solution for dummies. We expect our users that want professional results, to investigate what video and streaming is, and to read the ffmpeg encoding options.

[redsox_mark]

I am also seeing this issue. I understand the way VBR works, and that it is a target bitrate, but that does not explain what I am seeing.

I've tried different codecs and the same thing happens.

If I use a bitrate of say 3072k, and I monitor the bandwidth used, I see that it overs right around 3000-3200. If I pick 2048, the rates stay close to that. 1024 also works... it averages around 1024. But anything less than 1024 behaves the same as 1024! 512k, 256k... even if I use a setting of 16k the actual rate used averages around 1000k!

I hate using the "b" word, but I don't see how that can be correct. I want to stream over the internet to another PC using DSL, so I need to limit my rate. I tried the command line options as well and that didn't help.

Has anyone been successful at transcoding at low bit rates, and if so how?

Mark

[redsox_mark]

I've done some more investigation, which hopefully will be of use to someone..

What I found is that there seems to be a limit to how much compression VLC will do, and it varies depending on the size and/or bitrate of the original material.

In my previous post - where the source was a DVD quality MPEG2 stream (720x576, 6 Mbps bitrate), I found that no matter how low I set the transcode settings for the codec, it would not encode at less than (approx) 1 Mbps. Even if I used the lowest possible setting of 16k (for the video, plus 16k for the audio).

I tried the same tests with a different clip - this one was MPEG1, 368x228, encoded at 1.7 Mbps. This one VLC would encode at a lower rate - around 300k.

I tried with yet another clip - this one 192x114 MPEG1, encoded at 700k. VLC, with the codec set at 16k transcode, would encode at around 150k.

So it seems the max amount of compression VLC will do varies depending on the input. I'm not sure if it is exactly linear, but it seems that it won't compress more than around 6:1.

So as long as you aren't trying to compress more than that, it works fine. But if you want to take a high quality 6 Mbps stream and convert it to 300k or so (as I am), it won't do it. If you want to stream at 300k you have to find a way to reduce the size of the input before it gets to VLC.

Mark

[redsox_mark]

My extensive testing has shown that VLC seems limited to the amount of compression it will do - feed it a large bitrate input, and it simply will not encode at a low value. Unless there is some additional setting I've not been able to find.

I gave up and tried Windows Media Encoder - this worked perfectly. Was able to take a high quality input and convert it to a low bitrate (e.g. 340k, or lower if I wanted to), and stream over the internet.

I probably won't be popular for saying this on a VLC forum, but if you are windows based and having issues trying to stream at a low bitrate, try Microsoft Windows Media Encoder.

Mark

[gcovato]

Hi,

I confirm what all you explained. I tried everything possible to have a stream that doesn't go over my 256K connection. No way to do it.

I am trying to use it in a production enviroment.

Would be nice to know if there is any plan to analyze this problem.

Thank you

[DJ]

I believe that for any given resolution (size) there is a minimum bitrate. So if you want to go lower in bitrate reduce the size.