Re: [FFmpeg-devel] [PATCH] cbs_av1: Make fake OBU size length field a write option

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Mark Thompson:
> This is an option to modify the behaviour of the writer, not a syntax
> field.
> ---
> Tested by hacking av1_metadata.  For example, adding:
> 
> av_opt_set_int(ctx->common.output->priv_data, "fixed_obu_size_length",
> 7, 0);
> 
> gets you OBU headers that look like:
> 
> [trace_headers @ 0x55706fcb2880] OBU header
> [trace_headers @ 0x55706fcb2880] 0          
> obu_forbidden_bit                                           0 = 0
> [trace_headers @ 0x55706fcb2880] 1          
> obu_type                                                 0100 = 4
> [trace_headers @ 0x55706fcb2880] 5          
> obu_extension_flag                                          0 = 0
> [trace_headers @ 0x55706fcb2880] 6          
> obu_has_size_field                                          1 = 1
> [trace_headers @ 0x55706fcb2880] 7          
> obu_reserved_1bit                                           0 = 0
> [trace_headers @ 0x55706fcb2880] 8           obu_size 
> 10101110100010101000000010000000100000001000000000000000 = 1326
> 
> It's not obvious that there is any value in exposing this option more
> generally, though?  It could made a visible option of av1_metadata or
> others if there is any use-case for it.
> 
> Thanks,
> 
> - Mark
> 
> 
>  libavcodec/cbs_av1.c          | 31 +++++++++++++++++++++----------
>  libavcodec/cbs_av1.h          |  5 ++++-
>  libavcodec/vaapi_encode_av1.c |  4 +++-
>  3 files changed, 28 insertions(+), 12 deletions(-)

What is the advantage of this? Why would people want to waste space?

- Andreas

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