[FFmpeg-devel] [PATCH v2] libavformat/rtpdec_mpeg: handle bare ADTS packets with explicit decoder config

[lance.lmwang at gmail.com]

On Tue, Oct 19, 2021 at 05:02:44PM -0400, Jeff Mahoney wrote:

The title should be "avformat/rtpdec_mpeg4: ..." 

> When SDP specifies a decoder config, there may not be any AU headers
> provided by the sender.  This can result in rtp_parse_mp4_au failing
> and aac_parse_packet reporting "Error parsing AU headers." and no audio
> is recovered from the stream.
> 
> This commit modifies aac_parse_header to check for an explicit decoder config
> set by the sdp parser (e.g. a:fmtp # config=hexvalue). If it has and there
> is an ADTS header present, it skips the header and copies the RTP
> payload directly as an AAC packet.
> 
> This resolves an issue observed with some inexpensive IP cameras.

How to test the issue without such IP cameras? 

> 
> Signed-off-by: Jeff Mahoney <jeffm at jeffm.io>
> ---
>  libavformat/rtpdec_mpeg4.c | 37 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/rtpdec_mpeg4.c b/libavformat/rtpdec_mpeg4.c
> index 34c7950bcc..13d0770dd6 100644
> --- a/libavformat/rtpdec_mpeg4.c
> +++ b/libavformat/rtpdec_mpeg4.c
> @@ -32,6 +32,8 @@
>  #include "libavutil/attributes.h"
>  #include "libavutil/avstring.h"
>  #include "libavcodec/get_bits.h"
> +#include "libavcodec/adts_header.h"
> +#include "libavcodec/adts_parser.h"
>  
>  #define MAX_AAC_HBR_FRAME_SIZE 8191
>  
> @@ -176,7 +178,7 @@ static int aac_parse_packet(AVFormatContext *ctx, PayloadContext *data,
>                              int flags)
>  {
>      int ret;
> -
> +    AVCodecParameters *par = st->codecpar;
>  
>      if (!buf) {
>          if (data->cur_au_index > data->nb_au_headers) {
> @@ -204,6 +206,39 @@ static int aac_parse_packet(AVFormatContext *ctx, PayloadContext *data,
>          return 1;
>      }
>  
> +    /* Check for an explicit decoder config (e.g. SDP a:fmtp... config=) */
> +    if (par->extradata && len > 7) {

7 is better to use AV_AAC_ADTS_HEADER_SIZE like the following.

> +        AACADTSHeaderInfo *header;
> +
> +        /*
> +         * Check for ADTS header
> +         * If present skip the header and copy the entire payload as AAC data
> +         */
> +        ret = avpriv_adts_header_parse(&header, buf, len);

need add adts_header dependency for rtp demuer. 


> +        if (!ret) {
> +            buf += AV_AAC_ADTS_HEADER_SIZE;
> +            len -= AV_AAC_ADTS_HEADER_SIZE;
> +
> +            /* Skip 16-bit CRC if present */
> +            if (!header->crc_absent) {
> +                buf += 2;
> +                len -= 2;
> +            }
> +            av_free(header);
> +
> +            ret = av_new_packet(pkt, len);
> +            if (ret < 0) {
> +                av_log(ctx, AV_LOG_ERROR, "Out of memory\n");
> +                return ret;
> +            }
> +
> +            memcpy(pkt->data, buf, len);
> +            pkt->stream_index = st->index;
> +
> +            return 0;
> +        }
> +    }
> +
>      if (rtp_parse_mp4_au(data, buf, len)) {
>          av_log(ctx, AV_LOG_ERROR, "Error parsing AU headers\n");
>          return -1;
> -- 
> 2.33.1
> 
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> 
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".

-- 
Thanks,
Limin Wang