[FFmpeg-trac] #11546(avcodec:new): mjpeg file call av_read_frame return EOF after seek

[FFmpeg]

#11546: mjpeg file call av_read_frame return EOF after seek
------------------------------------+--------------------------------------
             Reporter:  honglongyu  |                     Type:  defect
               Status:  new         |                 Priority:  normal
            Component:  avcodec     |                  Version:  git-master
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
------------------------------------+--------------------------------------
 I'm working on a looped decoding scenario for MJPEG files, and I
 encountered an issue when seeking back to the beginning of the file.
 Specifically, after calling av_seek_frame(fmt_ctx, -1, 0,
 AVSEEK_FLAG_BACKWARD), the first packet returned by av_read_frame() is
 immediately an EOF.


 Below is a minimal demo of my decoding code:


 {{{
 #include <iostream>
 extern "C" {
 #include <libavformat/avformat.h>
 #include <libavcodec/avcodec.h>
 }
 int main() {
     const char* filename =
         "D:\\dev\\8k_main\\8k\\example\\decode_pic\\test.jpg";
     AVFormatContext* formatContext = nullptr;
     if (avformat_open_input(&formatContext, filename, nullptr, nullptr) !=
 0) {
         std::cerr << "Could not open file: " << filename << std::endl;
         return -1;
     }
     if (avformat_find_stream_info(formatContext, nullptr) < 0) {
         std::cerr << "FFmpeg failed to find stream info: " << filename
                   << std::endl;
         return -1;
     }
     av_dump_format(formatContext, 0, filename, 0);
     int ret_seek = av_seek_frame(formatContext, 0, 0,
 AVSEEK_FLAG_BACKWARD);
     if (ret_seek < 0) {
         std::cerr << "Error seeking to frame" << std::endl;
         avformat_close_input(&formatContext);
         return -1;
     }
     // Read a frame from the file
     AVPacket packet;
     int ret = av_read_frame(formatContext, &packet);
     if (ret < 0) {
         char errbuf[AV_ERROR_MAX_STRING_SIZE] = {0};
         av_strerror(ret, errbuf, sizeof(errbuf));
         std::cerr << "Error reading frame, err is " << errbuf <<
 std::endl;
         av_packet_unref(&packet);
         avformat_close_input(&formatContext);
         return -1;
     }
     std::cout << "Frame read successfully" << std::endl;
     return 0;
 }
 }}}



 Here is the console output with seek:


 {{{
 Input #0, image2, from 'D:\dev\8k_main\8k\example\decode_pic\test.jpg':
   Duration: 00:00:00.04, start: 0.000000, bitrate: 551200 kb/s
   Stream #0:0: Video: mjpeg (Baseline), yuvj420p(pc,
 bt470bg/unknown/unknown), 3840x2160 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 25
 tbn
 Error reading frame, err is End of file
 }}}


 And here is the output without calling seek:

 {{{
 Input #0, image2, from 'D:\dev\8k_main\8k\example\decode_pic\test.jpg':
   Duration: 00:00:00.04, start: 0.000000, bitrate: 551200 kb/s
   Stream #0:0: Video: mjpeg (Baseline), yuvj420p(pc,
 bt470bg/unknown/unknown), 3840x2160 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 25
 tbn
 Frame read successfully
 }}}
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11546>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker