[FFmpeg-devel] Re: [PATCH] avformat/mpjpegdec: add support for X-Timestamp and X-Framerate headers

[Michael Niedermayer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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Hi Vladimir

On Sun, Nov 09, 2025 at 02:38:56AM +0200, Vladimir Sobolev via ffmpeg-devel wrote:
> >From 31d73c6774c1ea6d621db57f26439e297cc23c3d Mon Sep 17 00:00:00 2001
> From: Vladimir Sobolev <v.sobolev@gmail.com>
> Date: Sun, 9 Nov 2025 02:28:13 +0200
> Subject: [PATCH] avformat/mpjpegdec: add support for X-Timestamp and
>  X-Framerate headers
> 
> Add support for parsing X-Timestamp and X-Framerate headers from
> HTTP multipart MJPEG streams. These headers allow servers to provide
> accurate timestamps and framerate information for each frame.
> 
> Changes:
> - Parse X-Timestamp header (in seconds) and set packet PTS/DTS
> - Parse X-Framerate/X-FrameRate header and update stream framerate
> - Maintain backward compatibility (defaults to 25 fps if not provided)
> - Add debug logging for parsed header values
> 
> This enables proper timestamp handling for MJPEG streams that provide
> timing information in HTTP headers, improving synchronization accuracy.
> ---
>  libavformat/mpjpegdec.c | 69 ++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 65 insertions(+), 4 deletions(-)
> 
> diff --git a/libavformat/mpjpegdec.c b/libavformat/mpjpegdec.c
> index 125b17585e..c90d7a2ad4 100644
> --- a/libavformat/mpjpegdec.c
> +++ b/libavformat/mpjpegdec.c
> @@ -22,6 +22,9 @@
>  #include "libavutil/avstring.h"
>  #include "libavutil/mem.h"
>  #include "libavutil/opt.h"
> +#include "libavutil/parseutils.h"
> +#include "libavutil/eval.h"
> +#include "libavutil/intfloat.h"
>  
>  #include "avformat.h"
>  #include "demux.h"
> @@ -34,6 +37,11 @@ typedef struct MPJPEGDemuxContext {
>      char       *searchstr;
>      int         searchstr_len;
>      int         strict_mime_boundary;
> +    AVRational  framerate;      /* framerate from X-Framerate header */
> +    int64_t     timestamp;      /* timestamp from X-Timestamp header */
> +    int         has_timestamp;  /* flag indicating if timestamp was set */
> +    int         framerate_set; /* flag indicating if framerate was set in header */
> +    int         framerate_applied; /* flag indicating if framerate was applied to stream */
>  } MPJPEGDemuxContext;
>  
>  static void trim_right(char *p)
> @@ -97,7 +105,8 @@ static int split_tag_value(char **tag, char **value, char *line)
>  static int parse_multipart_header(AVIOContext *pb,
>                                      int* size,
>                                      const char* expected_boundary,
> -                                    void *log_ctx);
> +                                    void *log_ctx,
> +                                    MPJPEGDemuxContext *mpjpeg);
>  
>  static int mpjpeg_read_close(AVFormatContext *s)
>  {
> @@ -118,7 +127,7 @@ static int mpjpeg_read_probe(const AVProbeData *p)
>  
>      ffio_init_read_context(&pb, p->buf, p->buf_size);
>  
> -    ret = (parse_multipart_header(&pb.pub, &size, "--", NULL) >= 0) ? AVPROBE_SCORE_MAX : 0;
> +    ret = (parse_multipart_header(&pb.pub, &size, "--", NULL, NULL) >= 0) ? AVPROBE_SCORE_MAX : 0;
>  
>      return ret;
>  }
> @@ -146,6 +155,12 @@ static int mpjpeg_read_header(AVFormatContext *s)
>      st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
>      st->codecpar->codec_id   = AV_CODEC_ID_MJPEG;
>  
> +    /* Default framerate is 25 fps, will be updated from headers if available */
> +    MPJPEGDemuxContext *mpjpeg = s->priv_data;
> +    mpjpeg->framerate = (AVRational){25, 1};
> +    mpjpeg->framerate_set = 0;
> +    mpjpeg->framerate_applied = 0;
> +    mpjpeg->has_timestamp = 0;
>      avpriv_set_pts_info(st, 60, 1, 25);
>  
>      avio_seek(s->pb, pos, SEEK_SET);
> @@ -167,7 +182,8 @@ static int parse_content_length(const char *value)
>  static int parse_multipart_header(AVIOContext *pb,
>                              int* size,
>                              const char* expected_boundary,
> -                            void *log_ctx)
> +                            void *log_ctx,
> +                            MPJPEGDemuxContext *mpjpeg)
>  {
>      char line[128];
>      int found_content_type = 0;
> @@ -235,6 +251,33 @@ static int parse_multipart_header(AVIOContext *pb,
>                  av_log(log_ctx, AV_LOG_WARNING,
>                             "Invalid Content-Length value : %s\n",
>                             value);
> +        } else if (mpjpeg && !av_strcasecmp(tag, "X-Timestamp")) {
> +            double ts = av_strtod(value, NULL);

> +            if (!isnan(ts) && isfinite(ts)) {

nan is not finite


> +                /* X-Timestamp is in seconds, convert to AV_TIME_BASE */
> +                mpjpeg->timestamp = (int64_t)(ts * AV_TIME_BASE);
> +                mpjpeg->has_timestamp = 1;
> +                if (log_ctx)
> +                    av_log(log_ctx, AV_LOG_DEBUG,
> +                           "Parsed X-Timestamp: %s -> %"PRId64" (%.6f seconds)\n",
> +                           value, mpjpeg->timestamp, ts);
> +            } else if (log_ctx) {
> +                av_log(log_ctx, AV_LOG_WARNING,
> +                       "Invalid X-Timestamp value : %s\n", value);
> +            }
> +        } else if (mpjpeg && (!av_strcasecmp(tag, "X-Framerate") || !av_strcasecmp(tag, "X-FrameRate"))) {
> +            AVRational fps = {0};
> +            if (av_parse_video_rate(&fps, value) >= 0 && fps.num > 0 && fps.den > 0) {
> +                mpjpeg->framerate = fps;
> +                mpjpeg->framerate_set = 1;
> +                if (log_ctx)
> +                    av_log(log_ctx, AV_LOG_DEBUG,
> +                           "Parsed X-Framerate: %s -> %d/%d fps\n",
> +                           value, fps.num, fps.den);
> +            } else if (log_ctx) {
> +                av_log(log_ctx, AV_LOG_WARNING,
> +                       "Invalid X-Framerate value : %s\n", value);
> +            }

all the if(log_ctx) looks wierd i dont think log_ctx is ever NULL in this code thats under if(mpjpeg)


>          }
>      }
>  
> @@ -311,10 +354,21 @@ static int mpjpeg_read_packet(AVFormatContext *s, AVPacket *pkt)
>          mpjpeg->searchstr_len = strlen(mpjpeg->searchstr);
>      }
>  
> -    ret = parse_multipart_header(s->pb, &size, mpjpeg->boundary, s);
> +    /* Reset timestamp flag for each packet */
> +    mpjpeg->has_timestamp = 0;
> +
> +    ret = parse_multipart_header(s->pb, &size, mpjpeg->boundary, s, mpjpeg);
>      if (ret < 0)
>          return ret;
>  
> +    /* Update framerate if it was set in header and hasn't been applied yet */
> +    if (mpjpeg->framerate_set && !mpjpeg->framerate_applied && s->nb_streams > 0) {
> +        AVStream *st = s->streams[0];
> +        st->avg_frame_rate = mpjpeg->framerate;
> +        avpriv_set_pts_info(st, 60, mpjpeg->framerate.den, mpjpeg->framerate.num);
> +        mpjpeg->framerate_applied = 1;
> +    }

this looks wrong
* you should not set the timebase more than once. it was already set to 1/25

* the average framerate can only match the 1/timebase for "constant fps"
  which is the opposit of what this patch is trying to do




> +
>      if (size > 0) {
>          /* size has been provided to us in MIME header */
>          ret = av_get_packet(s->pb, pkt, size);
> @@ -353,6 +407,13 @@ static int mpjpeg_read_packet(AVFormatContext *s, AVPacket *pkt)
>          }
>      }
>  
> +    /* Set timestamp from X-Timestamp header if available */
> +    if (ret >= 0 && mpjpeg->has_timestamp && s->nb_streams > 0) {
> +        AVStream *st = s->streams[0];

> +        pkt->pts = av_rescale_q(mpjpeg->timestamp, AV_TIME_BASE_Q, st->time_base);

rescaling timestamps suggests you set the timebase wrong

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

What does censorship reveal? It reveals fear. -- Julian Assange

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