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

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

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.

> +
> +    // +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

> +    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.)

> +    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:

> +    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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