Re: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer: Added demuxer to handle reading EVC video files

["Dawid Kozinski/Multimedia \(PLT\) /SRPOL/Staff Engineer/Samsung Electronics" <d.kozinski@samsung.com>]

> -----Original Message-----
> From: Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff Engineer/Samsung
> Electronics <d.kozinski@samsung.com>
> Sent: środa, 7 czerwca 2023 17:41
> To: 'FFmpeg development discussions and patches' <ffmpeg-
> devel@ffmpeg.org>
> Subject: RE: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer: Added
> demuxer to handle reading EVC video files
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> > James Almer
> > Sent: środa, 7 czerwca 2023 15:40
> > To: ffmpeg-devel@ffmpeg.org
> > Subject: Re: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer:
> > Added demuxer to handle reading EVC video files
> >
> > On 6/7/2023 10:36 AM, Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff
> > Engineer/Samsung Electronics wrote:
> > >
> > >
> > >
> > >> -----Original Message-----
> > >> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> > >> James Almer
> > >> Sent: poniedziałek, 29 maja 2023 15:08
> > >> To: ffmpeg-devel@ffmpeg.org
> > >> Subject: Re: [FFmpeg-devel] [PATCH v23 04/10] avformat/evc_demuxer:
> > >> Added demuxer to handle reading EVC video files
> > >>
> > >> On 5/26/2023 7:31 AM, Dawid Kozinski wrote:
> > >>> +static int get_temporal_id(const uint8_t *bits, int bits_size) {
> > >>> +    int temporal_id = 0;
> > >>> +    short t = 0;
> > >>> +
> > >>> +    if (bits_size >= EVC_NALU_HEADER_SIZE) {
> > >>> +        unsigned char *p = (unsigned char *)bits;
> > >>> +        // forbidden_zero_bit
> > >>> +        if ((p[0] & 0x80) != 0)
> > >>> +            return -1;
> > >>> +
> > >>> +        for (int i = 0; i < EVC_NALU_HEADER_SIZE; i++)
> > >>> +            t = (t << 8) | p[i];
> > >>
> > >> I think this can be replaced with AV_RB16.
> > >>
> > >>> +
> > >>> +        temporal_id = (t >> 6) & 0x0007;
> > >>> +    }
> > >>> +
> > >>> +    return temporal_id;
> > >>> +}
> > >>
> > >> [...]
> > >>
> > >>> +static uint32_t read_nal_unit_length(const uint8_t *bits, int
> > >>> +bits_size) {
> > >>> +    uint32_t nalu_len = 0;
> > >>> +
> > >>> +    if (bits_size >= EVC_NALU_LENGTH_PREFIX_SIZE) {
> > >>> +
> > >>> +        int t = 0;
> > >>> +        unsigned char *p = (unsigned char *)bits;
> > >>> +
> > >>> +        for (int i = 0; i < EVC_NALU_LENGTH_PREFIX_SIZE; i++)
> > >>> +            t = (t << 8) | p[i];
> > >>
> > >> AV_RB32.
> > >>
> > >>> +
> > >>> +        nalu_len = t;
> > >>> +        if (nalu_len == 0)   // Invalid bitstream size
> > >>> +            return 0;
> > >>> +    }
> > >>> +
> > >>> +    return nalu_len;
> > >>> +}
> > >>
> > >> [...]
> > >>
> > >>> +static int evc_frame_merge_filter(AVBSFContext *bsf, AVPacket *out) {
> > >>> +    EVCMergeContext *ctx = bsf->priv_data;
> > >>> +    AVPacket *in = ctx->in;
> > >>> +
> > >>> +    int free_space = 0;
> > >>> +    size_t  nalu_size = 0;
> > >>> +    uint8_t *nalu = NULL;
> > >>> +    int au_end_found = 0;
> > >>> +    int err;
> > >>> +
> > >>> +    err = ff_bsf_get_packet_ref(bsf, in);
> > >>> +    if (err < 0)
> > >>> +        return err;
> > >>> +
> > >>> +    nalu_size = read_nal_unit_length(in->data,
> > >> EVC_NALU_LENGTH_PREFIX_SIZE);
> > >>> +    if(nalu_size <= 0) {
> > >>> +        av_packet_unref(in);
> > >>> +        return AVERROR_INVALIDDATA;
> > >>> +    }
> > >>> +
> > >>> +    nalu = in->data + EVC_NALU_LENGTH_PREFIX_SIZE;
> > >>> +    nalu_size = in->size - EVC_NALU_LENGTH_PREFIX_SIZE;
> > >>> +
> > >>> +    // NAL unit parsing needed to determine if end of AU was found
> > >>> +    err = parse_nal_unit(nalu, nalu_size, bsf);
> > >>> +    if (err < 0) {
> > >>> +        av_log(bsf, AV_LOG_ERROR, "NAL Unit parsing error\n");
> > >>> +        av_packet_unref(in);
> > >>> +
> > >>> +        return err;
> > >>> +    }
> > >>> +
> > >>> +    au_end_found = end_of_access_unit_found(bsf);
> > >>> +
> > >>> +    free_space = ctx->au_buffer.capacity - ctx->au_buffer.data_size;
> > >>> +    while( free_space < in->size ) {
> > >>> +        ctx->au_buffer.capacity *= 2;
> > >>> +        free_space = ctx->au_buffer.capacity -
> > >>> + ctx->au_buffer.data_size;
> > >>> +
> > >>> +        if(free_space >= in->size) {
> > >>> +            ctx->au_buffer.data = av_realloc(ctx->au_buffer.data,
> > >>> + ctx-
> > >>> au_buffer.capacity);
> > >>> +        }
> > >>> +    }
> > >>> +
> > >>> +    memcpy(ctx->au_buffer.data + ctx->au_buffer.data_size,
> > >>> + in->data,
> > >>> + in->size);
> > >>
> > >> This is including the Annex-B's nal_unit_lenght value into the
> > >> assembled
> > > packet. I
> > >> assume libxevd expects this? Also, is it defined as part of the
> > >> ISOBMFF encapsulation? Patch 07/10 does not seem to strip it.
> > >
> > > Could you expand on this topic?
> > > What do you mean by "Patch 07/10 does not seem to strip it"?
> > > Patch 7/10 expands the implementation of the MOV Muxer to support
> > > the EVC stream.
> > > The function ff_isom_write_evcc parses the received data, extracts
> > > NAL units of types SPS, PPS, APS, SEI, and inserts their contents
> > > into the corresponding elements of the arrays array, which is a
> > > component of the EVCDecoderConfigurationRecord structure.
> > > Additionally, the ff_isom_write_evcc function populates the relevant
> > > fields of the EVCDecoderConfigurationRecord structure based on the
> > > parsed SPS NAL unit data, and then calls the evcc_write function,
> > > which writes the EVCDecoderConfigurationRecord to the stream.
> > >
> > > It seems that I don't understand what's wrong with our
> > > implementation ( I mean MOV muxer for EVC) and it seems I need your
> > > help in this matter. I need an explanation of what's wrong and what
> > > should be done to fix
> > the issue.
> >
> > I mean the packets that go into ISOBMFF Sample, not the evcc atom. Is
> > the encapsulation supposed to include the nal_unit_length from Annex-B?
> 
> The function mov_write_single_packet(s, pkt) receives packets containing the
> Access Units (AU) of an EVC stream. Each AU consists of a sequence of NAL
> units, each preceded by a 4-byte prefix that contains information about the
> length of the NAL unit. The entire AU is then copied to AVIOContext using
> avio_write(pb, pkt->data, size).
> 

It seems to me that everything is okay. If I am mistaken, just let me know. 
As we have also completed all the fixes following your review this is the last thing blocking us from creating a new patchset.

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