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Bug 719697 - encoder: h264: allow user-defined number of reference frames
encoder: h264: allow user-defined number of reference frames
Status: RESOLVED OBSOLETE
Product: GStreamer
Classification: Platform
Component: gstreamer-vaapi
git master
Other Linux
: Normal enhancement
: git master
Assigned To: GStreamer Maintainers
GStreamer Maintainers
Depends on:
Blocks: 758397
 
 
Reported: 2013-12-02 16:42 UTC by Gwenole Beauchesne
Modified: 2018-11-03 15:43 UTC
See Also:
GNOME target: ---
GNOME version: ---


Description Gwenole Beauchesne 2013-12-02 16:42:17 UTC 
We need to provide a way to specify how many reference frames are allowed. This covers both L0 and L1 lists, if B-frames are used.

- "ref": number of reference frames to use (default: 1)
Comment 1 xiaowei 2013-12-12 08:11:24 UTC 
Hi, 

  Our h264 encoder only supports one reference at most due to driver's limitation. do we really need to specify the reference number? it will not improve the compression rate substantially.
Comment 2 Gwenole Beauchesne 2013-12-12 12:30:31 UTC 
Hi,

(In reply to comment #1)
>   Our h264 encoder only supports one reference at most due to driver's
> limitation. do we really need to specify the reference number? it will not
> improve the compression rate substantially.

When do you think the limitation is to be lifted? I thought we supported up to 4 nowadays.

The idea here was not about improving the compression ratio, but rather improve the perceived visual quality. In x264, it looks like raising the number of reference frames from 1 to 3 makes it possible to gain ~0.25 dB in PSNR.

Meanwhile, I am OK to drop this from 0.5.8 requirements then. Thanks.
Comment 3 xiaowei 2013-12-13 00:44:40 UTC 
   Now in encoding driver, the VME shaders support 2 refs for B dual direction predict, and support only 1 for P frame, although the packing command support 4 reference information, but VME only provide 2 refs info at most.
  we have ever discussed about expanding the reference frame count, but VME shaders need to be rewrited, it will take many efforts to achive, so we'd better defer this bug fixing.
Comment 4 Gwenole Beauchesne 2014-06-25 04:11:27 UTC 
Postponed to a later stage when the driver supports more than 1-2 refs.

As per comment #3, the HW can really support up to 16 refs, even back to Sandybridge (with restrictions). This is what multipass is for. Though, up to 4 would be enough to me.
Comment 5 GStreamer system administrator 2018-11-03 15:43:55 UTC 
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

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