[FFmpeg-trac] #1098(avfilter:open): ass subtitle are stretched

FFmpeg trac at avcodec.org
Mon Mar 19 18:18:39 CET 2012

#1098: ass subtitle are stretched
             Reporter:  fate        |                    Owner:
                 Type:  defect      |                   Status:  open
             Priority:  normal      |                Component:  avfilter
              Version:  git-master  |               Resolution:
             Keywords:  ass         |               Blocked By:
             Blocking:              |  Reproduced by developer:  1
Analyzed by developer:  1           |

Comment (by dbuitenh):

 Replying to [comment:7 saste]:
 > The problem depends on the fact that vf_ass.c uses the same DAR of input
 for rendering the subtitles, which is indeed a rather arbitrary behavior
 (see line in vf_ass.c: ass_set_aspect_ratio(ass->renderer, dar, sar)).
 > Possible fixes:
 > set the DAR to 1.0, or allow the user to specify the DAR through an
 > In the second case I ask: does it make sense to be able to set such
 value, or should be rather set in the ass file itself (assuming it is

 The thing that everyone who uses VSFilter on windows (thus defining the
 behavior for other players and libs) has been doing since time immortal is
 to manually set the x/y resize factors in the .ass file. i.e. something
 with a 32:27 PAR -> x = (27 / 32) = 84.275%, y = 100 %. VSFilter then
 applies these at a 1.0 DAR, and then the renderer resizes on playback as
 the very last step.

 To sum up: VSFilter always applies at 1.0 DAR.

Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1098#comment:9>
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