[FFmpeg-soc] Extend TSMuxer to H264 muxing

[zhentan feng]

Hi

2008/4/15, Michael Niedermayer <michaelni at gmx.at>:
>
> On Tue, Apr 15, 2008 at 09:33:34PM +0800, zhentan feng wrote:
> > Hi
> >
> > 2008/4/14, Baptiste Coudurier <baptiste.coudurier at smartjog.com>:
> > >
> > > On Mon, Apr 14, 2008 at 02:40:54PM +0800, zhentan feng wrote:
> > > > [...]
> > > >
> > > > > > +                if(st->codec->codec_id == CODEC_ID_H264){
> > >
> > > > > > +                    H264Context * h_st = st->codec->priv_data;
> > > > >
> > > > > This is invalid, there is a reason why its called priv_data, and
> that
> > > is
> > > > > that it is private to the codec.
> > > >
> > > > I think it is the key point to write descriptors into PMT for AVC
> > > stream.
> > > > Can't I get the h264 codec information when init TS out stream?
> > > > Do you mean the *priv_data* only could be used by libavcodec
> functions,
> > > we
> > > > can't read some information from it by other extern functions?
> > > > If so, I am a little confused how could I get information when init
> the
> > > > descriptor?
> > > >
> > >
> > >
> > > No you cannot, only libavcodec h264 decoder is allowed to use
> priv_data,
> > > TS muxer has to parse PPS/PPS and gather needed infos.
> >
> >
> > Here is the  new patch names "h264_desc_aud_patch4-15.diff" attached
> below.
> >
> > 1,Add a new struct MpegTSH264Desc in MpegTSWriteStream to collect
> > information of AVC stream descriptors.
> > 2,Parser the SPS and VUI to write descriptor into PMT.
> > 3,Check the AUD nal units. if pkt don't have ,then insert AUD nal units
> into
> > the AVPacket data.
> >
> > Thanks for your any advice and best wishes.
>
> [...]
> > +void pre_decode_vui(MpegTSH264Desc * h_dsc, GetBitContext *gb)
> > +{
> > +    int aspect_ratio_info_present_flag;
> > +    unsigned int aspect_ratio_idc;
> > +    int nal_hrd_parameters_present_flag,
> vcl_hrd_parameters_present_flag;
> > +    aspect_ratio_info_present_flag= get_bits1(gb);
> >
> > +    if(aspect_ratio_info_present_flag){
> > +        aspect_ratio_idc= get_bits(gb, 8);
> > +        if(aspect_ratio_idc == EXTENDED_SAR){
> > +            get_bits(gb, 16);
> > +            get_bits(gb, 16);
> > +        }else if(sizeof(pixel_aspect)/sizeof(*pixel_aspect) <=
> aspect_ratio_idc){
> > +            return -1;
> > +        }
> > +    }
> > +
> > +    if(get_bits1(gb)){      /* overscan_info_present_flag */
> > +        get_bits1(gb);      /* overscan_appropriate_flag */
> > +    }
> > +
> > +    if(get_bits1(gb)){      /* video_signal_type_present_flag */
> > +        get_bits(gb, 3);    /* video_format */
> > +        get_bits1(gb);      /* video_full_range_flag */
> > +        if(get_bits1(gb)){  /* colour_description_present_flag */
> > +            get_bits(gb, 8); /* colour_primaries */
> > +            get_bits(gb, 8); /* transfer_characteristics */
> > +            get_bits(gb, 8); /* matrix_coefficients */
> > +        }
> > +    }
>
> duplicate of decode_vui_parameters()


 Yes, it is a duplicate code from H264.c.
I am in a dillema to handle the problem :
When init TS muxer , I should read some information about AVC stream from
H264Context, which is priv_data of AVCodecContext(libavcodec) so, I cannot
get them directly from upper level(libavformat).

I think it may has 4 ways to handle the peoblem:

1, Decode the SPS by TS muxer and *don't* reuse the code of h264.c

At libavformat level, just parser the AVC data independently from AVPacket
and get information what we need. Because we don't  need all information of
the H264Context, so we can simplify the decode process.

That's just my latest patch method to do. So, this causes some duplicate
code with H264 decode of h264.c.

2, Decode the SPS by TS muxer and reuse the code of h264.c
This method will change some code of h264.c to export the interface, so it
may break up the logic level process and encapsulation of the H264 decoder.

3, Don't decode the SPS by TS muxer and get the information by add a new
struct in AVCodecContext, such as MpegTSH264Desc.
When decode the H264 stream, we can write useful information into
MpegTSH264Desc and will be later fecthed by the upper level.But we still
decode the AVC stream to check the AUD nal units, if the pkt->data donnot
have the AUD, we should insert AUD nal units to the AVC stream before muxing
into PES packet.

Any ideas about the methods?

thanks.

-- 
Best wishes~