B1W low bit rate VBR (Variable Bit Rate)

[chaveiro]

I just analysed the recorded files of low bit rate and indeed they are MP4 12Mbps and 4Mbps for parking mode, but it seems to be using a CBR (constant bit rate mode) codec.

Could it be possible to have a beta version using VBR (variable bit rate) so that we can squeeze even more from data on the sdcard.

The rational is that by using VBR the max bit rate is still capped to 12 or 4 Mbps but we get savings on less complex images or stills (eg. the car is parked on a dark garage) that reduce file size.

 

[Nigel]

No dashcam maker has yet perfected variable bitrate!

Normally variable bitrate is not used for live recording, it is used for re-encoding where the content of the video stream can be analysed into the future so that an appropriate bitrate can be used while encoding to get the maximum compression for archiving, in fact for H26? it is normally a two pass process, although not always.

At 4 Mbps parking mode, you can get a decent amount of video on a card anyway, if you need more then fit a bigger card.

 

[chaveiro]

Nigel, not sure if what you said is a myth or some limitation from a specific product.
I work on the iptv industry and i'm sure highend enconders do VBR on live streaming and it's required or bandwidth costs would sky rocket.
If it's a 2 pass or not process it's just a technicality omitted from the configuration interface.
Anyway see this
https://ipvm.com/reports/vbr-vs-cbr-surveillance-streaming

 

[Nigel]

Nigel, not sure if what you said is a myth or some limitation from a specific product.
I work on the iptv industry and i'm sure highend enconders do VBR on live streaming and it's required or bandwidth costs would sky rocket.
If it's a 2 pass or not process it's just a technicality omitted from the configuration interface.
Anyway see this
https://ipvm.com/reports/vbr-vs-cbr-surveillance-streaming

IPTV is a bit different since your often recording mainly static scenes so VBR would make a lot of sense, dashcams when not parked have a huge amount of movement to record so need high bitrates all they time. Things like YouTube normally use fixed bitrate at whatever bitrate the link can support to get best quality. What I wrote in my previous post isn't exactly correct, a lot of our dashcams do use variable bitrate, but limit the range so that it is effectively fixed, or close to fixed. Still not seen any dashcam actually succeed in lowering bitrate effectively when you might think it is easily done, hence the need for a seperate low bitrate parking mode. If variable bitrate really worked then there would be no need to switch to parking mode.

 

[chaveiro]

Lets hear first if its supported or not by the camera chipset.
@estore009 can you check if VBR could be possible on this hardware?

 

[jokiin]

most chipsets support it, the results aren't great though, CBR offers consistent results and a better end result

 

[chaveiro]

If you encode a video at 4Mbit CBR and 4Mbit VBR the VBR can have better quality. This is because it will vary the bitrate perhaps giving some frames as much as 6 or 7Mbit while others only 1 or 2Mbit but in the end it will average out to 4Mbit. CBR, on the other hand, will never give any frame more that 4Mbit. If there are frames that need more than 4Mbit to encode, CBR will look worse than VBR.

I'd like to have some beta firmware to test

 

[Nigel]

If you encode a video at 4Mbit CBR and 4Mbit VBR the VBR can have better quality. This is because it will vary the bitrate perhaps giving some frames as much as 6 or 7Mbit while others only 1 or 2Mbit but in the end it will average out to 4Mbit. CBR, on the other hand, will never give any frame more that 4Mbit. If there are frames that need more than 4Mbit to encode, CBR will look worse than VBR.

I'd like to have some beta firmware to test

Not sure that is true, I think even CBR will vary the bitrate on frames that are close together, you could have exactly 4Mb/second and have big variation over the 30 frames within the second.

The big problem is that with a dashcam we are not really interested in the quality when there is nothing happening, we are interested when a massive amount happens, rather different than in CCTV where even when something happens, it probably affects a small part of the image and normally happens fairly slowly compared to a crash.

 

[jokiin]

I think you're applying what you know from your industry in the hopes that it will work the same on different hardware

 

[estore009]

Lets hear first if its supported or not by the camera chipset.
@estore009 can you check if VBR could be possible on this hardware?

Same as @jokiin said, the B1W dashcam chipset supports it! Not sure if it works great. I think our tech support will give it a try in our spare time...

 

[chaveiro]

Thank you @estore009, i thing if correcly done it could be a different approuch that keeps the same image quality (or more as explained above) while increasing 30-40% SD-Card hours storage.
I propose to start with the CBR low bitrate firmware and approach like:
- nomal recording VBR limited to max 12Mpbs
- low bit rate mode VBR limited to max 4Mbps