What are the disadvantages of intra_refresh?

Albert6677 · 18th January 2021, 03:45

I am new in the RTC field.
Could you please tell me what are the disadvantages of intra_refresh?
After reading Salsify and WebRTC's source code, I found that they do not use this mechanism.
In my opinion, intra_refresh can benefit us a lot. It could not overshoot the bandwidth in most of the time, because of no IDR frame.
So could you please tell me why they do not use intra_refresh?

Blue_MiSfit · 19th January 2021, 07:02

Good question! It's unfathomable to me to use single frame VBV (when targeting low latency) without intra refresh! That keyframe pumping is ruinous.

benwaggoner · 20th January 2021, 18:03

Intra refresh also can really improve quality when there is packet loss, which is pretty inevitable when using low-latency UDP in RTC. If an IDR is corrupted, the rest of the GOP is likely unwatchable. But with intra refresh, you get periodic refreshes for macroblocks which future frames can then reference, so over time quality is restored without a full IDR.

One can think of it is having IDRs for macroblocks instead of frames.

They're not great for random access, but that's not a key RTC scenario.

Encoding and playback are really different above and below 1 sec of latency!

18th January 2021, 03:45	#1 \| Link
Albert6677 Registered User Join Date: Jan 2021 Posts: 2	What are the disadvantages of intra_refresh? I am new in the RTC field. Could you please tell me what are the disadvantages of intra_refresh? After reading Salsify and WebRTC's source code, I found that they do not use this mechanism. In my opinion, intra_refresh can benefit us a lot. It could not overshoot the bandwidth in most of the time, because of no IDR frame. So could you please tell me why they do not use intra_refresh?

20th January 2021, 18:03	#3 \| Link
benwaggoner Moderator Join Date: Jan 2006 Location: Portland, OR Posts: 4,653	Intra refresh also can really improve quality when there is packet loss, which is pretty inevitable when using low-latency UDP in RTC. If an IDR is corrupted, the rest of the GOP is likely unwatchable. But with intra refresh, you get periodic refreshes for macroblocks which future frames can then reference, so over time quality is restored without a full IDR. One can think of it is having IDRs for macroblocks instead of frames. They're not great for random access, but that's not a key RTC scenario. Encoding and playback are really different above and below 1 sec of latency! __________________ Ben Waggoner Principal Video Specialist, Amazon Prime Video My Compression Book

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19th January 2021, 07:02	#2 \| Link
Blue_MiSfit Derek Prestegard IRL Join Date: Nov 2003 Location: Los Angeles Posts: 5,980	Good question! It's unfathomable to me to use single frame VBV (when targeting low latency) without intra refresh! That keyframe pumping is ruinous.