I have a project that I would like to export for a DVD project. I decided to base my settings on the DVD preset that is available. However, it seems that when it comes to DVDs the Rate Control in the Codec tab is very different. The DVD preset changes it to Constant Bitrate as opposed to Average Bitrate (what I am used to) and from that point on I don’t know how to configure the Bitrate to get the results that I want.
The Constant Bitrate option gives the additional settings for “Buffer Size” which I don’t understand. I don’t know a low or high setting for Buffer Size would be in the context of DVDs. I was thinking of just matching that to whatever the Buffer Size was for the original file but I don’t know how to get the information for that.
I figured I would just leave the Buffer Size as the Shotcut presets are (224) and just change the Bitrate to how I want it. I set the Bitrate high (9000k) and then I tried to export it. Well, the results were a file that were far lower than the original. The original video size was 4.29 GiB. The file that came back was barely over a GiB.
I would appreciate help on all of my questions here as I am totally lost.
Thanks and here is the video info on the original file:
Video ID : 1 Format : MPEG Video Format version : Version 2 Format profile : Main@Main Format settings, BVOP : Yes Format settings, Matrix : Custom Format settings, GOP : Variable Format settings, picture struc : Frame Codec ID : V_MPEG2 Codec ID/Info : MPEG 1 or 2 Video Duration : 1 h 22 min Bit rate mode : Variable Bit rate : 7 450 kb/s Maximum bit rate : 9 800 kb/s Width : 720 pixels Height : 576 pixels Display aspect ratio : 16:9 Frame rate mode : Constant Frame rate : 25.000 FPS Standard : Component Color space : YUV Chroma subsampling : 4:2:0 Bit depth : 8 bits Scan type : Interlaced Scan order : Top Field First Compression mode : Lossy Bits/(Pixel*Frame) : 0.719 Time code of first frame : 09:59:59:00 Time code source : Group of pictures header GOP, Open/Closed : Open GOP, Open/Closed of first fram : Closed Stream size : 4.29 GiB (84%) Default : Yes Forced : No Color primaries : BT.601 PAL Transfer characteristics : BT.470 System B, BT.470 System G Matrix coefficients : BT.601
I made an account today to just let you know how utterly useless your reply is. These are good questions and your link is total garbage: There’s nothing about buffer sizes for Constant Bitrate.
I too want to know about what the buffer size does and the effects of altering the default value, as I was mistakenly using Constant Bitrate (because apparently Average Bitrate is closer to actually being constant than the aforementioned option).
So if you asked a Policeman for directions to the local shopping mall and when you get there you can’t find the product you’re looking for you’d go back and find that Policeman and tell him his directions were useless and garbage?
There is no harm in reminding people to search.
In any case, CBR, in general does not necessarily give a truly constant rate bitstream. For example, the MLT engine has a special purpose MPEG-2 Transport Stream output plugin to achieve that. CBR typically means the rate does not cause some receiver and/or decoder buffer to underflow or overflow, and that is what is mean by buffer size. The smaller the buffer the more strict it must be. The current DVD preset buffer size is based on the FFmpeg preset buffer size:
And that was made to comply with DVD Video specification (see the ffmpeg source comment for how 224 KiB converts to the Mb/s per the spec.).
ABR is a form of VBR that hovers around a target bitrate, but since the buffer size is not constrained it will quite likely not result in being perfectly DVD Video compliant. It is quite likely that some - maybe yours - DVD player will not complain with ABR. It depends on what you intend to do with the DVD as far as distribution is concerned. I am not a DVD Video encoding expert, and there are probably changes you can make to get higher bitrate and better quality and still be compliant, but I do not know what they are.
Thank you so much for this! Even though Average Bitrate is what I’m now using for my video uploads, I was still curious about the purpose of the buffer for Constant Bitrate, and this answers everything. Thank you, again.
Thank you for supporting my question. As you yourself have noted, the link that Steve put up was indeed garbage and my question wasn’t even addressed. I didn’t say anything because I’ve already had issues with him before and I didn’t want to start something again. While there have been some good help on this forum and I do really appreciate that one of my suggestions for modifying one of the features on Shotcut was done on an update, there also has been needless friction with some of the people here. I once asked about an issue that Shotcut has with constant frame rates when it comes to mkv containers and the “shotcut leader” here got pissed off and closed my thread for no reason. It’s one of the reasons I rarely visit this forum. There’s no reason for stuff like that.
Your original post went unanswered for a month, when you asked for help again. @Steve_Ledger responded. Are you saying it would have been better that Steve ignored you like everyone else did? Maybe I’m getting a bit off topic here, as I’ve read many of Steve’s replies to many threads in here and I learn a lot from Steve along with a few others.
