[FFmpeg-user] Not able to creating high-quality jpegs/mjpegs

[Paul B Mahol]

On 9/22/13, Robert Krueger <krueger at lesspain.de> wrote:
> On Sun, Sep 22, 2013 at 2:03 AM, Paul B Mahol <onemda at gmail.com> wrote:
>> On 9/21/13, Robert Krueger <krueger at lesspain.de> wrote:
>>> On Fri, Sep 20, 2013 at 11:55 PM, Paul B Mahol <onemda at gmail.com> wrote:
>>>> On 9/20/13, Robert Krueger <krueger at lesspain.de> wrote:
>>>>> Hi,
>>>>>
>>>>> jpeg/mjpeg compression seems to have a certain limit that I am not
>>>>> able to exceed and that is significantly lower than that of other
>>>>> graphics programs.
>>>>>
>>>>> To test I took a png image (a still frame exported from a video) in
>>>>> 1920x1080 and converted it to jpeg like so
>>>>>
>>>>> ffmpeg -i test.png -c:v mjpeg -q:v 1 test-ffmpeg.jpg
>>>>
>>>> -q:v 0 ?
>>>
>>> same result. The files are bit-identical.
>>
>> -qmin 1 -qmax 1
>>
>> I forgot this and searched web to learn it again.
>
> That doubled the bitrate. Thanks. ffmpeg rate control is indeed a
> mysterious art that only few really understand ;-).
>
> I would like to compare psnr for all these different versions but
> somehow I am not doing it right. I could swear that I have used the
> psnr filter like this before but now I can't get it to work.
>
> I first converted the files (original and compressed versions) into
> ffv1 with yuv444p pixel format, so the pixel formats match for psnr
> comparison and are supported by the psnr filter. Then I used the
> command line below and got no psnr output (stats.log is empty as
> well). I have used this command line with other files before and it
> worked (I may overlook something, of course), so I am guessing now,
> what I am doing wrong. I cannot see any error message either.
>
> ffmpeg -i test-ffmpeg-g5-ffv1.mkv -vf "movie=test-ffv1.mkv,
> setpts=PTS-STARTPTS [main]; [main][ref] psnr="stats_file=stats.log"
> [out]" -f null /dev/null
> ffmpeg version N-56463-g20101f4 Copyright (c) 2000-2013 the FFmpeg
> developers
>   built on Sep 19 2013 20:18:44 with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
>   configuration:
>   libavutil      52. 44.100 / 52. 44.100
>   libavcodec     55. 33.100 / 55. 33.100
>   libavformat    55. 18.100 / 55. 18.100
>   libavdevice    55.  3.100 / 55.  3.100
>   libavfilter     3. 86.102 /  3. 86.102
>   libswscale      2.  5.100 /  2.  5.100
>   libswresample   0. 17.103 /  0. 17.103
> Input #0, matroska,webm, from 'test-ffmpeg-g5-ffv1.mkv':
>   Metadata:
>     ENCODER         : Lavf55.18.100
>   Duration: 00:00:00.04, start: 0.000000, bitrate: 52926 kb/s
>     Stream #0:0: Video: ffv1 (FFV1 / 0x31564646), yuv444p, 1920x1080,
> SAR 1:1 DAR 16:9, 25 fps, 25 tbr, 1k tbn, 1k tbc (default)
> Output #0, null, to '/dev/null':
>   Metadata:
>     encoder         : Lavf55.18.100
>     Stream #0:0: Video: rawvideo (444P / 0x50343434), yuv444p,
> 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 90k tbn, 25 tbc
> (default)
> Stream mapping:
>   Stream #0:0 -> #0:0 (ffv1 -> rawvideo)
> Press [q] to stop, [?] for help
> [null @ 0x7fe30381a000] Encoder did not produce proper pts, making some up.
> frame=    1 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
> video:0kB audio:0kB subtitle:0 global headers:0kB muxing overhead
> -122.916667%
>
> Any ideas, what I am doing wrong here?

If there is only one frame it will not work... its bug I hope will be
fixed soon.