On 26/09/2023 10:19, Andreas Rheinhardt wrote:
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?
Because they want to be able to write a different size into the field later
without realigning all the following bytes.
VAAPI seems to require this, hence the previous code which added a fake syntax
element field to the OBU structure containing the size to be written with,
which this patch is replacing with an external option.
Thanks,
- Mark
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