[FFmpeg-devel] [PATCH v3] avformat/rtpdec_rfc4175: support non-zero based line numbers

[Kah Goh]

On Mon, Sep 30, 2019 at 09:27:20PM +0800, Kah Goh wrote:
> There are differing standards that define different starting line
> numbers. For example, VSF TR-03 says the line numbers starts at 1,
> whereas SMPTE 2110-20 says it should start at 0.
> 
> This change adds support for non-zero based line numbers and addresses
> the following issues when it starts at 1:
> - The first scan line was being incorrectly interpreted as the second
>   scan line. This means the first line in the frame was never being
>   populated.
> - The last packet for the video frame would be treated as invalid
>   because it would have been copied outside of the frame. Consequently,
>   the packet would never be "finalized" and the next packet triggers a
>   missed RTP marker ("Missed previous RTP marker" would keep being
>   logged).
> 
> VSF TR-03: http://www.videoservicesforum.org/download/technical_recommendations/VSF_TR-03_2015-11-12.pdf
> 
> Co-Authored-By: Jacob Siddall <kobe at live.com.au>
> Co-Authored-By: Kah Goh <villastar at yahoo.com.au>
> Signed-off-by: Kah Goh <villastar at yahoo.com.au>
> ---
>  libavformat/rtpdec_rfc4175.c | 49 +++++++++++++++++++++++++++++++++---
>  1 file changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/libavformat/rtpdec_rfc4175.c b/libavformat/rtpdec_rfc4175.c
> index e9c62c1389..47d5d23dd6 100644
> --- a/libavformat/rtpdec_rfc4175.c
> +++ b/libavformat/rtpdec_rfc4175.c
> @@ -25,6 +25,7 @@
>  #include "rtpdec_formats.h"
>  #include "libavutil/avstring.h"
>  #include "libavutil/pixdesc.h"
> +#include <stdbool.h>
>  
>  struct PayloadContext {
>      char *sampling;
> @@ -37,6 +38,12 @@ struct PayloadContext {
>      unsigned int pgroup; /* size of the pixel group in bytes */
>      unsigned int xinc;
>  
> +    /* The line number of the first line in the frame (usually either 0 or 1). */
> +    int first_line_number;
> +
> +    /* This is set to true once the first line number is confirmed. */
> +    bool first_line_number_known;
> +
>      uint32_t timestamp;
>  };
>  
> @@ -136,6 +143,13 @@ static int rfc4175_finalize_packet(PayloadContext *data, AVPacket *pkt,
>     return ret;
>  }
>  
> +static int rfc4175_initialize(AVFormatContext *s, int st_index, PayloadContext *data)
> +{
> +    data->first_line_number = 0;
> +    data->first_line_number_known = false;
> +    return 0;
> +}
> +
>  static int rfc4175_handle_packet(AVFormatContext *ctx, PayloadContext *data,
>                                   AVStream *st, AVPacket *pkt, uint32_t *timestamp,
>                                   const uint8_t * buf, int len,
> @@ -188,7 +202,7 @@ static int rfc4175_handle_packet(AVFormatContext *ctx, PayloadContext *data,
>  
>      /* and now iterate over every scan lines */
>      do {
> -        int copy_offset;
> +        int copy_offset, copy_to_line;
>  
>          if (payload_len < data->pgroup)
>              return AVERROR_INVALIDDATA;
> @@ -199,17 +213,34 @@ static int rfc4175_handle_packet(AVFormatContext *ctx, PayloadContext *data,
>          cont = headers[4] & 0x80;
>          headers += 6;
>  
> +        if (line == 0) {
> +            data->first_line_number = 0;
> +            data->first_line_number_known = true;
> +        }
> +
>          if (length % data->pgroup)
>              return AVERROR_INVALIDDATA;
>  
>          if (length > payload_len)
>              length = payload_len;
>  
> -        /* prevent ill-formed packets to write after buffer's end */
> -        copy_offset = (line * data->width + offset) * data->pgroup / data->xinc;
> -        if (copy_offset + length > data->frame_size)
> +        copy_to_line = line - data->first_line_number;
> +        if (copy_to_line < 0)
> +            /* This means the first line number we have calculated is too large, which indicates that we
> +            may have received some bad data. */
>              return AVERROR_INVALIDDATA;
>  
> +        /* prevent ill-formed packets to write after buffer's end */
> +        copy_offset = (copy_to_line * data->width + offset) * data->pgroup / data->xinc;
> +        if (copy_offset + length > data->frame_size) {
> +            if (data->first_line_number_known)
> +                return AVERROR_INVALIDDATA;
> +
> +            // This would happen if the line numbering is 1 based. We still need to check for the RTP flag
> +            // marker (as per after the while loop).
> +            break;
> +        }
> +
>          dest = data->frame + copy_offset;
>          memcpy(dest, payload, length);
>  
> @@ -218,6 +249,15 @@ static int rfc4175_handle_packet(AVFormatContext *ctx, PayloadContext *data,
>      } while (cont);
>  
>      if ((flags & RTP_FLAG_MARKER)) {
> +        if (!data->first_line_number_known) {
> +            data->first_line_number = line - data->height + 1;
> +            if (data->first_line_number < 0) {
> +                // This could happen if the frame does not fill up the entire height.
> +                data->first_line_number = 0;
> +                av_log(ctx, AV_LOG_WARNING, "Video frame does not fill entire height");
> +            }
> +            data->first_line_number_known = true;
> +        }
>          return rfc4175_finalize_packet(data, pkt, st->index);
>      } else if (missed_last_packet) {
>          return 0;
> @@ -232,5 +272,6 @@ const RTPDynamicProtocolHandler ff_rfc4175_rtp_handler = {
>      .codec_id           = AV_CODEC_ID_BITPACKED,
>      .priv_data_size     = sizeof(PayloadContext),
>      .parse_sdp_a_line   = rfc4175_parse_sdp_line,
> +    .init               = rfc4175_initialize,
>      .parse_packet       = rfc4175_handle_packet,
>  };
> -- 
> 2.23.0
>

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