[FFmpeg-devel] [RFC PATCH 3/4] avcodec/hevcdec: add nuh_layer_id option

["zhilizhao(赵志立)"]

> On Jan 5, 2023, at 19:21, James Almer <jamrial at gmail.com> wrote:
> 
> On 1/5/2023 1:14 PM, Zhao Zhili wrote:
>> From: Zhao Zhili <zhilizhao at tencent.com>
>> It can be used to decode selected independent non-base layer. One
>> use case is alpha layer decoding.
>> Signed-off-by: Zhao Zhili <zhilizhao at tencent.com>
>> ---
>>  libavcodec/hevcdec.c | 20 +++++++++++++++++++-
>>  libavcodec/version.h |  2 +-
>>  2 files changed, 20 insertions(+), 2 deletions(-)
>> diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
>> index 567e8d81d4..9641922834 100644
>> --- a/libavcodec/hevcdec.c
>> +++ b/libavcodec/hevcdec.c
>> @@ -3216,7 +3216,8 @@ static int decode_nal_units(HEVCContext *s, const uint8_t *buf, int length)
>>            if (s->avctx->skip_frame >= AVDISCARD_ALL ||
>>              (s->avctx->skip_frame >= AVDISCARD_NONREF
>> -            && ff_hevc_nal_is_nonref(nal->type)) || nal->nuh_layer_id > 0)
>> +            && ff_hevc_nal_is_nonref(nal->type)) ||
>> +            nal->nuh_layer_id != s->nuh_layer_id)
>>              continue;
>>            ret = decode_nal_unit(s, nal);
>> @@ -3637,6 +3638,21 @@ static av_cold int hevc_decode_init(AVCodecContext *avctx)
>>      HEVCContext *s = avctx->priv_data;
>>      int ret;
>>  +    if (s->nuh_layer_id > 0) {
>> +        if (avctx->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) {
>> +            av_log(avctx, AV_LOG_ERROR,
>> +                    "Decode selected nuh_layer_id is undef development. "
>> +                    "Use -strict -2 to use it anyway.\n");
> 
> "Undef development"? Does decoding of these non-base layers work or not? One thing is something being experimental (thus known to be working in at least some cases, even if not spec compliant), and another is enabling something we don't know if it's going to work or not at all.

Undef -> Under.

It works for INBL (independent non-base layer) bitstream, which is coded
without using inter-layer prediction and conforms to a single layer profile.
Apple’s "HEVC Video with Alpha Interoperability Profile” is this case from
my test, although Apple doesn’t specify it clear.

https://developer.apple.com/av-foundation/HEVC-Video-with-Alpha-Interoperability-Profile.pdf

Whether it’s INBL can be checked from vps_extension, which doesn’t get parsed
yet.

There are at least three ways to add multi-layer extension support:
1. Fully support inside hevc soft decoder, with inter-layer prediction support,
multiview and spatial scalability and so on.

2. A decoder wrapper, which has two or multi hevc decoder instances inside.
Only works for INBL streams.

3. Let user handle multiple decoder instances. Only works from INBL streams.

> 
>> +            return AVERROR(EINVAL);
>> +        }
>> +
>> +        if (avctx->hwaccel) {
>> +            av_log(avctx, AV_LOG_ERROR,
>> +                    "Decode selected nuh_layer_id doesn't work with hwaccel.\n");
>> +            return AVERROR(EINVAL);
>> +        }
>> +    }
>> +
>>      if (avctx->active_thread_type & FF_THREAD_SLICE) {
>>          s->threads_number = avctx->thread_count;
>>          ret = ff_slice_thread_init_progress(avctx);
>> @@ -3691,6 +3707,8 @@ static const AVOption options[] = {
>>          AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, PAR },
>>      { "strict-displaywin", "stricly apply default display window size", OFFSET(apply_defdispwin),
>>          AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, PAR },
>> +    { "nuh_layer_id", "Select which nuh_layer_id to decode (only works with INBL)", OFFSET(nuh_layer_id),
>> +        AV_OPT_TYPE_INT,  {.i64 = 0}, 0, 62, PAR },
>>      { NULL },
>>  };
>>  diff --git a/libavcodec/version.h b/libavcodec/version.h
>> index 6b8a1dbb79..15f7c3fe3d 100644
>> --- a/libavcodec/version.h
>> +++ b/libavcodec/version.h
>> @@ -30,7 +30,7 @@
>>  #include "version_major.h"
>>    #define LIBAVCODEC_VERSION_MINOR  56
>> -#define LIBAVCODEC_VERSION_MICRO 100
>> +#define LIBAVCODEC_VERSION_MICRO 101
>>    #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
>>                                                 LIBAVCODEC_VERSION_MINOR, \
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