Re: [FFmpeg-devel] [PATCH v5] avcodec/libx264: fix extradata when config annexb=0

[Zhao Zhili <quinkblack@foxmail.com>]

> On Mar 14, 2024, at 21:14, Andreas Rheinhardt <andreas.rheinhardt@outlook.com> wrote:
> 
> Zhao Zhili:
>> From: Zhao Zhili <zhilizhao@tencent.com>
>> 
>> ---
>> v5: Decode chroma_format_idc directly instead of ff_h264_decode_seq_parameter_set
>> v4: Fix missing SEI in set_avcc_extradata
>> v3: Remove unnecessary inclusion
>> 
>> libavcodec/libx264.c | 162 ++++++++++++++++++++++++++++++++++++-------
>> 1 file changed, 138 insertions(+), 24 deletions(-)
>> 
>> diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
>> index 10d646bd76..64cefb5fb0 100644
>> --- a/libavcodec/libx264.c
>> +++ b/libavcodec/libx264.c
>> @@ -38,6 +38,7 @@
>> #include "packet_internal.h"
>> #include "atsc_a53.h"
>> #include "sei.h"
>> +#include "golomb.h"
>> 
>> #include <x264.h>
>> #include <float.h>
>> @@ -865,6 +866,140 @@ static int convert_pix_fmt(enum AVPixelFormat pix_fmt)
>>     return 0;
>> }
>> 
>> +static int save_sei(AVCodecContext *avctx, x264_nal_t *nal)
>> +{
>> +    X264Context *x4 = avctx->priv_data;
>> +
>> +    av_log(avctx, AV_LOG_INFO, "%s\n", nal->p_payload + 25);
>> +    x4->sei_size = nal->i_payload;
>> +    x4->sei = av_malloc(x4->sei_size);
>> +    if (!x4->sei)
>> +        return AVERROR(ENOMEM);
>> +
>> +    memcpy(x4->sei, nal->p_payload, nal->i_payload);
>> +
>> +    return 0;
>> +}
>> +
>> +static int set_avcc_extradata(AVCodecContext *avctx, x264_nal_t *nal, int nnal)
>> +{
>> +    X264Context *x4 = avctx->priv_data;
>> +    x264_nal_t *sps_nal = NULL;
>> +    x264_nal_t *pps_nal = NULL;
>> +    uint8_t *p, *sps;
>> +    int ret;
>> +
>> +    /* 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++) {
>> +        switch (nal[i].i_type) {
>> +        case NAL_SPS:
>> +            sps_nal = &nal[i];
>> +            break;
>> +        case NAL_PPS:
>> +            pps_nal = &nal[i];
>> +            break;
>> +        case NAL_SEI:
>> +            ret = save_sei(avctx, &nal[i]);
>> +            if (ret < 0)
>> +                return ret;
>> +            break;
>> +        }
>> +    }
>> +    if (!sps_nal || !pps_nal)
>> +        return AVERROR_EXTERNAL;
>> +
>> +    avctx->extradata_size = sps_nal->i_payload + pps_nal->i_payload + 7;
>> +    avctx->extradata = av_mallocz(avctx->extradata_size + AV_INPUT_BUFFER_PADDING_SIZE);
>> +    if (!avctx->extradata)
>> +        return AVERROR(ENOMEM);
>> +
>> +    // Now create AVCDecoderConfigurationRecord
>> +    p = avctx->extradata;
>> +    // Skip size part
>> +    sps = sps_nal->p_payload + 4;
>> +    *p++ = 1; // version
>> +    *p++ = sps[1]; // AVCProfileIndication
>> +    *p++ = sps[2]; // profile_compatibility
>> +    *p++ = sps[3]; // AVCLevelIndication
>> +    *p++ = 0xFF;
>> +    *p++ = 0xE0 | 0x01; // 3 bits reserved (111) + 5 bits number of sps
>> +    memcpy(p, sps_nal->p_payload + 2, sps_nal->i_payload - 2);
>> +    // Make sps has AV_INPUT_BUFFER_PADDING_SIZE padding, so it can be used
>> +    // with GetBitContext
>> +    sps = p + 2;
>> +    p += sps_nal->i_payload - 2;
>> +    *p++ = 1;
>> +    memcpy(p, pps_nal->p_payload + 2, pps_nal->i_payload - 2);
>> +    p += pps_nal->i_payload - 2;
>> +
>> +    if (sps[3] != 66 && sps[3] != 77 && sps[3] != 88) {
>> +        GetBitContext gbc;
>> +        int chroma_format_idc;
>> +        int bit_depth_luma_minus8, bit_depth_chroma_minus8;
>> +
>> +        /* It's not possible to have emulation prevention byte before
>> +         * bit_depth_chroma_minus8 due to the range of sps id, chroma_format_idc
>> +         * and so on. So we can read directly without need to escape emulation
>> +         * prevention byte.
> 
> There is a slight problem here: You ignore the possibility of
> profile_idc being zero. After all, all values not being used are merely
> reserved and can be used at any time (although I doubt that they will
> ever use this). Shall we ignore this?
> The above check (and presumably the ISOBMFF spec for this) uses an
> opt-out check for profile, whereas the H.264 spec actually uses an
> opt-in check. I just wanted to mention it, feel free to ignore it.
> 
>> +         *
>> +         * +4 to skip until sps id.
>> +         */
>> +        init_get_bits8(&gbc, sps + 4, sps_nal->i_payload - 4 - 4);
>> +        // Skip sps id
>> +        get_ue_golomb_31(&gbc);
>> +        chroma_format_idc = get_ue_golomb_31(&gbc);
>> +        if (chroma_format_idc == 3)
>> +            skip_bits1(&gbc);
>> +        bit_depth_luma_minus8 = get_ue_golomb_31(&gbc);
>> +        bit_depth_chroma_minus8 = get_ue_golomb_31(&gbc);
>> +
>> +        *p++ = 0xFC | chroma_format_idc;
>> +        *p++ = 0xF8 | bit_depth_luma_minus8;
>> +        *p++ = 0xF8 | bit_depth_chroma_minus8;
>> +        *p++ = 0;
>> +    }
>> +    av_assert0(avctx->extradata + avctx->extradata_size >= p);
> 
> Does this have to be an av_assert0?

Switched to assert2 in v6. 

> 
>> +    avctx->extradata_size = p - avctx->extradata;
>> +
>> +    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) {
>> +            s = save_sei(avctx, &nal[i]);
>> +            if (s < 0)
>> +                return s;
>> +            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 +1368,9 @@ 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);
> 
> You need a golomb configure dependency for get_ue_golomb_31().

Select golomb in configure and use conditional compile in case of only
x262 is enabled. I think atsc_a53 has the same problem but it’s unrelated
to current patch.

> 
> - Andreas
> 
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