Re: [FFmpeg-devel] [PATCH v4] avcodec/libx264: fix extradata when config annexb=0

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

James Almer:
> On 3/12/2024 12:00 PM, Andreas Rheinhardt wrote:
>> Zhao Zhili:
>>> From: Zhao Zhili <zhilizhao@tencent.com>
>>>
>>> ---
>>> v4: Fix missing SEI in set_avcc_extradata
>>> v3: Remove unnecessary inclusion
>>>
>>>   configure            |   2 +-
>>>   libavcodec/libx264.c | 153 ++++++++++++++++++++++++++++++++++++-------
>>>   2 files changed, 130 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/configure b/configure
>>> index db7dc89755..24cb897d28 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..e7d16997d2 100644
>>> --- a/libavcodec/libx264.c
>>> +++ b/libavcodec/libx264.c
>>> @@ -34,6 +34,7 @@
>>>   #include "avcodec.h"
>>>   #include "codec_internal.h"
>>>   #include "encode.h"
>>> +#include "h264_ps.h"
>>>   #include "internal.h"
>>>   #include "packet_internal.h"
>>>   #include "atsc_a53.h"
>>> @@ -865,6 +866,131 @@ 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;
>>> +        H264ParamSets ps = { 0 };
>>> +
>>> +        init_get_bits8(&gbc, sps, sps_nal->i_payload - 4);
>>> +        skip_bits(&gbc, 8);
>>> +        ret = ff_h264_decode_seq_parameter_set(&gbc, avctx, &ps, 1);
>>
>> ff_h264_decode_seq_parameter_set() expects to read from a GetBitContext
>> whose buffer has already been stripped of 0x03 escape bytes. Your buffer
>> hasn't and therefore it is possible for this function to return an error
>> even when the input is fine.
> 
> Why would a buffer created by passing annexb=0 have the escape bytes? Is
> it not specific to that encapsulation, to prevent parsing image data as
> a start code?
> 

You seem to believe that just because the 0x03 are not really useful in
ISOBMFF, they are not used in ISOBMFF. This is just not true. The 0x03
are not specific to annex B (they are not even defined in annex B; they
are defined in the most basic syntax structure of H.264: nal_unit, see
7.3.1 of the spec).
(If it were otherwise, our annex b->isobmff code in lavf would need to
strip it and our isobmff->annex b bsfs would need to escape the buffers,
which they don't.)

>>
>>> +        if (ret < 0)
>>> +            return ret;
>>> +
>>> +        ps.sps = ps.sps_list[x4->params.i_sps_id];
>>> +        *p++ = 0xFC | ps.sps->chroma_format_idc;
>>> +        *p++ = 0xF8 | (ps.sps->bit_depth_luma - 8);
>>> +        *p++ = 0xF8 | (ps.sps->bit_depth_chroma - 8);
>>> +        *p++ = 0;
>>> +        ff_h264_ps_uninit(&ps);
>>> +    }
>>> +    av_assert0(avctx->extradata + avctx->extradata_size >= p);
>>> +    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 +1359,9 @@ 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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