Incorrect seeking/decoding for AVCHD file

[rmk]

It appears seeking is incorrect and a frame gets duplicated when dealing with the attached AVCHD sample.

Please check the output for the attached small sample file for the two command lines (file is 25 FPS AFAIK it is a PsF file):

ffmpeg -ss 0.04 -i gh2-50i-psf.mts -vframes 1 frame-2-ss.jpg
ffmpeg version N-50443-g454c5d1 Copyright (c) 2000-2013 the FFmpeg developers
  built on Mar  3 2013 11:03:34 with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
  configuration: 
  libavutil      52. 17.103 / 52. 17.103
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.102 / 54. 63.102
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 41.100 /  3. 41.100
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
Input #0, mpegts, from 'gh2-50i-psf.mts':
  Duration: 00:00:01.38, start: 0.710178, bitrate: 46737 kb/s
  Program 1 
    Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 192 kb/s
    Stream #0:2[0x1200]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)
Output #0, image2, to 'frame-2-ss.jpg':
  Metadata:
    encoder         : Lavf54.63.102
    Stream #0:0: Video: mjpeg, yuvj420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> mjpeg)
Press [q] to stop, [?] for help
[h264 @ 0x7fd3093c6000] Missing reference picture, default is 0
[h264 @ 0x7fd3093c6000] decode_slice_header error
frame=    1 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A    
video:138kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.015517%

and 

ffmpeg -i gh2-50i-psf.mts -vframes 8 frame-%d-vframes.jpg
ffmpeg version N-50443-g454c5d1 Copyright (c) 2000-2013 the FFmpeg developers
  built on Mar  3 2013 11:03:34 with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
  configuration: 
  libavutil      52. 17.103 / 52. 17.103
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.102 / 54. 63.102
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 41.100 /  3. 41.100
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
Input #0, mpegts, from 'gh2-50i-psf.mts':
  Duration: 00:00:01.38, start: 0.710178, bitrate: 46737 kb/s
  Program 1 
    Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 192 kb/s
    Stream #0:2[0x1200]: Subtitle: hdmv_pgs_subtitle ([144][0][0][0] / 0x0090)
Output #0, image2, to 'frame-%d-vframes.jpg':
  Metadata:
    encoder         : Lavf54.63.102
    Stream #0:0: Video: mjpeg, yuvj420p, 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> mjpeg)
Press [q] to stop, [?] for help
frame=    8 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.32 bitrate=N/A dup=1 drop=0    
video:1031kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.002084% 

Two things seem to be wrong: The seeking (-ss) does not produce the correct frame (it's equivalent to the 8th frame of the second command) and if just dumping frames, it seems the first frame is duplicated.

I ran into this when I noticed that our application, written based on libavcodec/avformat did not work correctly when seeking in these files. This is only an attempt to make this reproducible with ff* tools, because I hope the reason for the incorrect behaviour of avformat_seek_file for these files is the same as for the described ffmpeg behaviour but I do not know that for sure.

[rmk]

Uploaded the file to /incoming/ticket2336/gh2-50i-psf.mts

[Carl Eugen Hoyos]

(Iiuc, you are reporting two independent issues, please don't do that, it makes following tickets impossible, open one ticket per problem.)

The sample you uploaded starts with a keyframe, the next keyframe is the eighth frame, so seeking a very small amount of time will seek to the eighth frame, this is the only way seeking can work if you need the complete frame, you can use -flags2 showall if you want to seek exactly to the given time and don't care about keyframes (this is what MPlayer does for performance reasons). Move -ss in front of the output file to get a completely different behaviour that imo cannot really be called "seeking", instead it decodes all frames until the specified time.

Regarding your second problem, I have to guess (missing information) but I suspect you are choosing an output container that only supports constant frame rate. To achieve constant frame rate for the given sample, the first frame has to be duplicated, use -vsync 0 to avoid this.

[rmk]

To make that clear, my real problem ist that avformat_seek_file does not work as documented for these files and I am trying to find a way to file a ticket that makes it easy for you to reproduce that something is wrong with seeking, so maybe I should not have reported the other (accidental observation about the duplicated frame) and probably I failed with this attempt.

Sorry for wasting your time. I will think of another way to make that problem reproducible and prepare the next attempt better. If you could not throw away the file for a few more days, I would reference it in a new report or shall I just re-upload it then?