[FFmpeg-devel] RTP: get the buffer information of the RTP extension header.

Signed-off-by: wujian_nanjing <wujian2@huawei.com>
---
 libavcodec/avpacket.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 libavcodec/packet.h   | 17 +++++++++++++++++
 libavformat/demux.c   |  7 +++++++
 libavformat/rtpdec.c  | 37 ++++++++++++++++++++++++++++---------
 4 files changed, 96 insertions(+), 9 deletions(-)

Wujian(Chin):
> Signed-off-by: wujian_nanjing <wujian2@huawei.com>
> ---
>  libavcodec/avpacket.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  libavcodec/packet.h   | 17 +++++++++++++++++
>  libavformat/demux.c   |  7 +++++++
>  libavformat/rtpdec.c  | 37 ++++++++++++++++++++++++++++---------
>  4 files changed, 96 insertions(+), 9 deletions(-)
> 
> diff --git a/libavcodec/avpacket.c b/libavcodec/avpacket.c
> index bcbc416..45c131a 100644
> --- a/libavcodec/avpacket.c
> +++ b/libavcodec/avpacket.c
> @@ -46,6 +46,8 @@ void av_init_packet(AVPacket *pkt)
>      pkt->opaque               = NULL;
>      pkt->opaque_ref           = NULL;
>      pkt->time_base            = av_make_q(0, 1);
> +    pkt->ext                  = NULL;
> +    pkt->extlen               = 0;
>  }
>  #endif
>  
> @@ -109,6 +111,46 @@ int av_new_packet(AVPacket *pkt, int size)
>      return 0;
>  }
>  
> +static void av_packet_free_ext(AVPacket *pkt)
> +{
> +    if (!pkt)
> +        return;
> +
> +    if (pkt->ext) {
> +        av_free(pkt->ext);
> +        pkt->ext = NULL;
> +    }
> +
> +    pkt->extlen = 0;
> +}
> +
> +int av_set_packet_ext(AVPacket *pkt, uint8_t *buf, int len)
> +{
> +    if (!buf || (len <= 0))
> +        return 0;
> +
> +    if (pkt->ext == buf) {
> +        pkt->extlen = len;
> +        return 0;
> +    }
> +
> +    pkt->ext = av_malloc(len);
> +    pkt->extlen = len;
> +    (void)memcpy(pkt->ext, buf, len);
> +
> +    return 0;
> +}
> +
> +static int av_copy_packet_ext(AVPacket *pkt, const AVPacket *src)
> +{
> +    pkt->ext = NULL;
> +    pkt->extlen = 0;
> +
> +    av_set_packet_ext(pkt, src->ext, src->extlen);
> +
> +    return 0;
> +}
> +
>  void av_shrink_packet(AVPacket *pkt, int size)
>  {
>      if (pkt->size <= size)
> @@ -422,6 +464,7 @@ int av_packet_copy_props(AVPacket *dst, const AVPacket *src)
>  void av_packet_unref(AVPacket *pkt)
>  {
>      av_packet_free_side_data(pkt);
> +    av_packet_free_ext(pkt);
>      av_buffer_unref(&pkt->opaque_ref);
>      av_buffer_unref(&pkt->buf);
>      get_packet_defaults(pkt);
> @@ -456,6 +499,7 @@ int av_packet_ref(AVPacket *dst, const AVPacket *src)
>      }
>  
>      dst->size = src->size;
> +    av_copy_packet_ext(dst, src);
>  
>      return 0;
>  fail:
> diff --git a/libavcodec/packet.h b/libavcodec/packet.h
> index 404d520..137d1fa 100644
> --- a/libavcodec/packet.h
> +++ b/libavcodec/packet.h
> @@ -374,6 +374,13 @@ typedef struct AVPacket {
>      uint8_t *data;
>      int   size;
>      int   stream_index;
> +
> +    /**
> +     * Extension header data and size
> +     */
> +    uint8_t *ext;
> +    uint32_t extlen;
> +
>      /**
>       * A combination of AV_PKT_FLAG values
>       */
> @@ -523,6 +530,16 @@ void av_init_packet(AVPacket *pkt);
>  int av_new_packet(AVPacket *pkt, int size);
>  
>  /**
> + * Allocate the ext data from buf with len lenght.
> + * Make sure pkt->ext is null, otherwise cause memory leak.
> + *
> + * @param pkt packet
> + * @param buf buffer with ext data
> + * @param len buffer size
> + */
> +int av_set_packet_ext(AVPacket *pkt, uint8_t *buf, int len);
> +
> +/**
>   * Reduce packet size, correctly zeroing padding
>   *
>   * @param pkt packet
> diff --git a/libavformat/demux.c b/libavformat/demux.c
> index 1620716..2a8b201 100644
> --- a/libavformat/demux.c
> +++ b/libavformat/demux.c
> @@ -1175,6 +1175,13 @@ static int parse_packet(AVFormatContext *s, AVPacket *pkt,
>              pkt->side_data_elems    = 0;
>          }
>  
> +        if (pkt->extlen > 0) {
> +            out_pkt->extlen = pkt->extlen;
> +            out_pkt->ext = pkt->ext;
> +            pkt->extlen = 0;
> +            pkt->ext = NULL;
> +        }
> +
>          /* set the duration */
>          out_pkt->duration = (sti->parser->flags & PARSER_FLAG_COMPLETE_FRAMES) ? pkt->duration : 0;
>          if (st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
> diff --git a/libavformat/rtpdec.c b/libavformat/rtpdec.c
> index fa7544c..2a539e0 100644
> --- a/libavformat/rtpdec.c
> +++ b/libavformat/rtpdec.c
> @@ -699,13 +699,14 @@ static int rtp_parse_packet_internal(RTPDemuxContext *s, AVPacket *pkt,
>  {
>      unsigned int ssrc;
>      int payload_type, seq, flags = 0;
> -    int ext, csrc;
> +    int has_ext, csrc, extlen;
> +    uint8_t *extbuf;
>      AVStream *st;
>      uint32_t timestamp;
>      int rv = 0;
>  
>      csrc         = buf[0] & 0x0f;
> -    ext          = buf[0] & 0x10;
> +    has_ext      = buf[0] & 0x10;
>      payload_type = buf[1] & 0x7f;
>      if (buf[1] & 0x80)
>          flags |= RTP_FLAG_MARKER;
> @@ -744,18 +745,25 @@ static int rtp_parse_packet_internal(RTPDemuxContext *s, AVPacket *pkt,
>          return AVERROR_INVALIDDATA;
>  
>      /* RFC 3550 Section 5.3.1 RTP Header Extension handling */
> -    if (ext) {
> +    if (has_ext) {
>          if (len < 4)
>              return -1;
>          /* calculate the header extension length (stored as number
>           * of 32-bit words) */
> -        ext = (AV_RB16(buf + 2) + 1) << 2;
> +        extlen = (AV_RB16(buf + 2) + 1) << 2;
>  
> -        if (len < ext)
> +        if (len < extlen)
>              return -1;
> -        // skip past RTP header extension
> -        len -= ext;
> -        buf += ext;
> +
> +         // Save RTP header extension data
> +        if (extlen > 0) {
> +            extbuf = av_malloc(extlen);
> +            if (extbuf)
> +                (void)memcpy(extbuf, buf, extlen);
> +        }
> +
> +        len -= extlen;
> +        buf += extlen;
>      }
>  
>      if (s->handler && s->handler->parse_packet) {
> @@ -763,14 +771,25 @@ static int rtp_parse_packet_internal(RTPDemuxContext *s, AVPacket *pkt,
>                                        s->st, pkt, &timestamp, buf, len, seq,
>                                        flags);
>      } else if (st) {
> -        if ((rv = av_new_packet(pkt, len)) < 0)
> +        if ((rv = av_new_packet(pkt, len)) < 0) {
> +            if ((extlen > 0) && extbuf)
> +                av_free(extbuf);
>              return rv;
> +        }
>          memcpy(pkt->data, buf, len);
>          pkt->stream_index = st->index;
>      } else {
> +        if ((extlen > 0) && extbuf)
> +            av_free(extbuf);
>          return AVERROR(EINVAL);
>      }
>  
> +    // attach ext data
> +    if ((extlen > 0) && extbuf) {
> +        av_set_packet_ext(pkt, extbuf, extlen);
> +        av_free(extbuf);
> +    }
> +
>      // now perform timestamp things....
>      finalize_packet(s, pkt, timestamp);
>  

1. Adding something in the middle of a public struct is an ABI break.
2. Currently sizeof(AVPacket) is still part of the public ABI, so one
can't even add something add the end of AVPacket.
3. But it doesn't matter, because such stuff belongs into packet side data.
4. The allocation in av_set_packet_ext() is unchecked.
5. Don't cast the return value of memcpy() to void.
6. There is a problem with parse_packet(): In case the parser adds
delay, the side data and (if this patch were merged as-is) also your
extension header data will end up with the wrong packet (if your parser
adds a one-packet delay, then packet n will end up with the side data
for packet n + 1). The reason for this is that the parsing API is
ancient and directly works with buffers and not with AVPackets.

- Andreas