P frame only intra refresh

sinkers · 2nd February 2021, 07:39

Is it possible with x264 to create a P frame only intra refresh stream/file?

I have a test file from another encoder that is all P frames + recovery points I am trying to recreate with this command:
x264 --input-res 1920x1080 --intra-refresh out.yuv --b-pyramid none --ref 0 -b 0 -o out.264

But I always get an I frame at the start

Blue_MiSfit · 2nd February 2021, 10:53

You sure the other encode wasn't trimmed?

benwaggoner · 2nd February 2021, 18:06

Quote:

Originally Posted by Blue_MiSfit

You sure the other encode wasn't trimmed?

Yeah, I can't imagine how else you could get a file like that. Since the first frame can't reference anything else, it has to be all-intra for it to be displayable.

sinkers · 2nd February 2021, 23:49

Quote:

Originally Posted by Blue_MiSfit

You sure the other encode wasn't trimmed?

Quite likely it was and I'll try trimming to regenerate. It was a capture from a live feed but it could be decoded and played back.

benwaggoner · 3rd February 2021, 04:34

Quote:

Originally Posted by sinkers

Quite likely it was and I'll try trimming to regenerate. It was a capture from a live feed but it could be decoded and played back.

Is the first frame playable by itself?

I think bidirectional prediction could be used to make a non-IDR first frame playable using intra refresh if predicted blocks in the first frame refer to intra blocks later in the GOP. But I'd be surprised someone would bother to make such an esoteric encoder feature. And that would require B-frames as well.

An interesting concept for a "crazy encoder stunt."

rwill · 3rd February 2021, 21:08

For streaming SPS and PPS have to be transferred for decode as well. When streaming with RTP or similar these are relayed by the application layer, which gets them from the encoder or from the start of the stream the encoder put out. I dont know if it is possible to insert SPS/PPS at random points at certain P frames with x264 out of the box. So you may need this first I frame for stream headers.

By the way you should use more reference frames than 0, more like 3 or 4.

benwaggoner · 3rd February 2021, 23:26

Quote:

Originally Posted by rwill

By the way you should use more reference frames than 0, more like 3 or 4.

Yeah, --ref 0 would be the same as --keyint 1, I'd think. All I-frames. Can't have a Predicted frame without a frame to predict from!

2nd February 2021, 07:39	#1 \| Link
sinkers Registered User Join Date: Oct 2012 Posts: 2	P frame only intra refresh Is it possible with x264 to create a P frame only intra refresh stream/file? I have a test file from another encoder that is all P frames + recovery points I am trying to recreate with this command: x264 --input-res 1920x1080 --intra-refresh out.yuv --b-pyramid none --ref 0 -b 0 -o out.264 But I always get an I frame at the start

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2nd February 2021, 10:53	#2 \| Link
Blue_MiSfit Derek Prestegard IRL Join Date: Nov 2003 Location: Los Angeles Posts: 5,960	You sure the other encode wasn't trimmed?

3rd February 2021, 21:08	#6 \| Link
rwill Registered User Join Date: Dec 2013 Posts: 279	For streaming SPS and PPS have to be transferred for decode as well. When streaming with RTP or similar these are relayed by the application layer, which gets them from the encoder or from the start of the stream the encoder put out. I dont know if it is possible to insert SPS/PPS at random points at certain P frames with x264 out of the box. So you may need this first I frame for stream headers. By the way you should use more reference frames than 0, more like 3 or 4.