Re: [FFmpeg-devel] [PATCH] avcodec/libx264: fix extradata when config annexb=0

["Zhao Zhili" <quinkblack@foxmail.com>]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Andreas Rheinhardt
> Sent: 2024年3月6日 22:19
> To: ffmpeg-devel@ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH] avcodec/libx264: fix extradata when config annexb=0
> 
> Zhao Zhili:
> > From: Zhao Zhili <zhilizhao@tencent.com>
> >
> > ---
> >  configure            |   2 +-
> >  libavcodec/libx264.c | 148 ++++++++++++++++++++++++++++++++++++-------
> >  2 files changed, 125 insertions(+), 25 deletions(-)
> >
> > diff --git a/configure b/configure
> > index bbf1a70731..ef58c3fe97 100755
> > --- a/configure
> > +++ b/configure
> > @@ -3491,7 +3491,7 @@ libwebp_encoder_deps="libwebp"
> >  libwebp_anim_encoder_deps="libwebp"
> >  libx262_encoder_deps="libx262"
> >  libx264_encoder_deps="libx264"
> > -libx264_encoder_select="atsc_a53"
> > +libx264_encoder_select="atsc_a53 h264parse"
> >  libx264rgb_encoder_deps="libx264"
> >  libx264rgb_encoder_select="libx264_encoder"
> >  libx265_encoder_deps="libx265"
> > diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
> > index 10d646bd76..10dfda125d 100644
> > --- a/libavcodec/libx264.c
> > +++ b/libavcodec/libx264.c
> > @@ -34,9 +34,12 @@
> >  #include "avcodec.h"
> >  #include "codec_internal.h"
> >  #include "encode.h"
> > +#include "get_bits.h"
> > +#include "h264_ps.h"
> >  #include "internal.h"
> >  #include "packet_internal.h"
> >  #include "atsc_a53.h"
> > +#include "put_bits.h"
> >  #include "sei.h"
> >
> >  #include <x264.h>
> > @@ -865,6 +868,124 @@ static int convert_pix_fmt(enum AVPixelFormat pix_fmt)
> >      return 0;
> >  }
> >
> > +static int set_avcc_extradata(AVCodecContext *avctx, x264_nal_t *nal, int nnal)
> > +{
> > +    x264_nal_t *sps_nal = NULL;
> > +    x264_nal_t *pps_nal = NULL;
> > +    GetBitContext gbc;
> > +    PutBitContext pbc;
> > +    H264ParamSets ps = { 0 };
> > +    uint8_t *p;
> > +    int ret, profile;
> > +
> > +    /* We know it's in the order of SPS/PPS/SEI, but it's not documented in x264 API.
> > +     * The x264 param i_sps_id implies there is a single pair of SPS/PPS.
> > +     */
> > +    for (int i = 0; i < nnal; i++) {
> > +        if (nal[i].i_type == NAL_SPS)
> > +            sps_nal = &nal[i];
> > +        else if (nal[i].i_type == NAL_PPS)
> > +            pps_nal = &nal[i];
> > +    }
> > +    av_assert0(sps_nal);
> > +    av_assert0(pps_nal);
> 
> We should never assert on the output of external libraries.

Ok, will just remove the assert. I don't think a check is needed.

> 
> > +
> > +    // +11 for AVCDecoderConfigurationRecord, will shrink to the real size finally
> > +    avctx->extradata_size = sps_nal->i_payload + pps_nal->i_payload + 11;
> > +    avctx->extradata = av_mallocz(avctx->extradata_size + AV_INPUT_BUFFER_MIN_SIZE);
> 
> AV_INPUT_BUFFER_PADDING_SIZE

Oops.

> 
> > +    if (!avctx->extradata)
> > +        return AVERROR(ENOMEM);
> > +
> > +    // Skip size part
> > +    p = sps_nal->p_payload + 4;
> > +    init_get_bits8(&gbc, p, sps_nal->i_payload - 4);
> > +    skip_bits(&gbc, 8);
> > +    ret = ff_h264_decode_seq_parameter_set(&gbc, avctx, &ps, 0);
> 
> This is completely overblown. You only read three fields: profile_idc,
> the constraint fields and level_idc. All three are at the start of the
> SPS and occupy a whole byte, so there is no need for a GetBitContext at all.
> (Yes, I am aware of the hypothetical scenario in which we could have a
> 0x03 escape byte before level_idc (in case of a hypothetical future
> profile zero), but even then using ff_h264_decode_seq_parameter_set() is
> overblown.)

You missed chroma_format_idc, bit_depth_luma/bit_depth_chroma.
I can get that from pixel format, but there are a lot of them.

> 
> > +    if (ret < 0)
> > +        return ret;
> > +
> > +    for (int i = 0; i < FF_ARRAY_ELEMS(ps.sps_list); i++) {
> > +        if (ps.sps_list[i]) {
> > +            ps.sps = ps.sps_list[i];
> > +            break;
> > +        }
> > +    }
> > +
> > +    // Now create AVCDecoderConfigurationRecord
> > +    init_put_bits(&pbc, avctx->extradata, avctx->extradata_size);
> > +    put_bits(&pbc, 8, 1); // version
> > +    put_bits(&pbc, 8, ps.sps->profile_idc); // AVCProfileIndication
> > +    put_bits(&pbc, 8, ps.sps->constraint_set_flags); // profile_compatibility
> > +    put_bits(&pbc, 8, ps.sps->level_idc); // AVCLevelIndication
> > +    put_bits(&pbc, 11, 0x7FF);
> > +
> > +    p = sps_nal->p_payload + 4;
> > +    put_bits(&pbc, 5, 1); // numOfSequenceParameterSets
> > +    put_bits(&pbc, 16, sps_nal->i_payload - 4); // sequenceParameterSetLength
> 
> I also think that using a PutBitContext is overblown here (most fields
> don't cross a byte-boundary, the bit-alignment of every field is fixed),
> in particular if you copy the NALUs eight bits at a time:

It's readable, close related to the spec, and it counts how many bytes actually used
automatically. I choose it for these convenience over performance.

> 
> > +    for (int i = 0; i < sps_nal->i_payload - 4; i++)
> > +        put_bits(&pbc, 8, p[i]);
> > +
> > +    p = pps_nal->p_payload + 4;
> > +    put_bits(&pbc, 8, 1); // numOfPictureParameterSets
> > +    put_bits(&pbc, 16, pps_nal->i_payload - 4); // pictureParameterSetLength
> > +    for (int i = 0; i < pps_nal->i_payload - 4; i++)
> > +        put_bits(&pbc, 8, p[i]);
> > +
> > +    profile = ps.sps->profile_idc;
> > +    if (profile != 66 && profile != 77 && profile != 88) {
> > +        put_bits(&pbc, 6, 0x3F);
> > +        put_bits(&pbc, 2, ps.sps->chroma_format_idc);
> > +        put_bits(&pbc, 5, 0x1F);
> > +        put_bits(&pbc, 3, ps.sps->bit_depth_luma - 8);
> > +        put_bits(&pbc, 5, 0x1F);
> > +        put_bits(&pbc, 3, ps.sps->bit_depth_chroma - 8);
> > +        put_bits(&pbc, 8, 0);
> > +    }
> > +    flush_put_bits(&pbc);
> > +    avctx->extradata_size = put_bytes_output(&pbc);
> > +
> > +    ff_h264_ps_uninit(&ps);
> > +
> > +    return 0;
> > +}
> > +
> > +static int set_extradata(AVCodecContext *avctx)
> > +{
> > +    X264Context *x4 = avctx->priv_data;
> > +    x264_nal_t *nal;
> > +    uint8_t *p;
> > +    int nnal, s;
> > +
> > +    s = x264_encoder_headers(x4->enc, &nal, &nnal);
> > +    if (s < 0)
> > +        return AVERROR_EXTERNAL;
> > +
> > +    if (!x4->params.b_annexb)
> > +        return set_avcc_extradata(avctx, nal, nnal);
> > +
> > +    avctx->extradata = p = av_mallocz(s + AV_INPUT_BUFFER_PADDING_SIZE);
> > +    if (!p)
> > +        return AVERROR(ENOMEM);
> > +
> > +    for (int i = 0; i < nnal; i++) {
> > +        /* Don't put the SEI in extradata. */
> > +        if (nal[i].i_type == NAL_SEI) {
> > +            av_log(avctx, AV_LOG_INFO, "%s\n", nal[i].p_payload + 25);
> > +            x4->sei_size = nal[i].i_payload;
> > +            x4->sei = av_malloc(x4->sei_size);
> > +            if (!x4->sei)
> > +                return AVERROR(ENOMEM);
> > +            memcpy(x4->sei, nal[i].p_payload, nal[i].i_payload);
> > +            continue;
> > +        }
> > +        memcpy(p, nal[i].p_payload, nal[i].i_payload);
> > +        p += nal[i].i_payload;
> > +    }
> > +    avctx->extradata_size = p - avctx->extradata;
> > +
> > +    return 0;
> > +}
> > +
> >  #define PARSE_X264_OPT(name, var)\
> >      if (x4->var && x264_param_parse(&x4->params, name, x4->var) < 0) {\
> >          av_log(avctx, AV_LOG_ERROR, "Error parsing option '%s' with value '%s'.\n", name, x4->var);\
> > @@ -1233,30 +1354,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
> >          return AVERROR_EXTERNAL;
> >
> >      if (avctx->flags & AV_CODEC_FLAG_GLOBAL_HEADER) {
> > -        x264_nal_t *nal;
> > -        uint8_t *p;
> > -        int nnal, s, i;
> > -
> > -        s = x264_encoder_headers(x4->enc, &nal, &nnal);
> > -        avctx->extradata = p = av_mallocz(s + AV_INPUT_BUFFER_PADDING_SIZE);
> > -        if (!p)
> > -            return AVERROR(ENOMEM);
> > -
> > -        for (i = 0; i < nnal; i++) {
> > -            /* Don't put the SEI in extradata. */
> > -            if (nal[i].i_type == NAL_SEI) {
> > -                av_log(avctx, AV_LOG_INFO, "%s\n", nal[i].p_payload+25);
> > -                x4->sei_size = nal[i].i_payload;
> > -                x4->sei      = av_malloc(x4->sei_size);
> > -                if (!x4->sei)
> > -                    return AVERROR(ENOMEM);
> > -                memcpy(x4->sei, nal[i].p_payload, nal[i].i_payload);
> > -                continue;
> > -            }
> > -            memcpy(p, nal[i].p_payload, nal[i].i_payload);
> > -            p += nal[i].i_payload;
> > -        }
> > -        avctx->extradata_size = p - avctx->extradata;
> > +        ret = set_extradata(avctx);
> > +        if (ret < 0)
> > +            return ret;
> >      }
> >
> >      cpb_props = ff_encode_add_cpb_side_data(avctx);
> 
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