Posted: Wed Aug 15, 2007 11:23 am
I have made a further observation and would be keen to have this confirmed by others. Even if you do cut clips on I- frames there is another artefact introduced by using Videostudio to add transitions between clips and smart rendering the final output.
I first noticed this when using Sektionschef's test.mpg
If you cut on frame at 3:21 using VS or another MPEG editor such as VideoRedo (3:21 on test.mpg is an I-frame) and put a transition ( I used 1 sec fade to black) and then smart render using VS there is a movement artefact seen at 4:05 - 4:09. There are 5 frames at this point that are all the same and it comes across as a movment artefact when the clip is played. It is more noticeable in some players compared to others. And obviously less noticeable if there is minimal movement in the scene. I couldn't see the stumble in Virtualdub or VideoRedo but it was obvious in PowerDVD, WMP, Media Player Classic. The "still" frames were most obvious if you enlarge the preview screen on VS 11+ and step thru the frames one by one at 4:04 to 4:09. It is almost as if these extra frames are used as padding - perhaps to complete a GOP?
I tried this with HD MPEG2 from my Sony HC3 and confirmed that even cutting on I Frames doesn't allow VS smart render to produce transitions without the introduction of an artefact.
I examined the GOP structure of my HD MPEG2. There are 12 frames from I-frame to I-frame. Cutting on the B frame prior to the I-frame produced the distorted frames. Cutting on any other frames produced the segment of "still" frames". The segment of still frames varied from about 5 frames near the I-frame down to 2 frames away from the I-Frame.
I have yet to confirm that this movement artefact happens with all transitions and cuts when editing with VS, but all the single 22 cuts I produced at different times in the same 10 sec segment of HD MPEG from my Sony HC3 all had either the distorted frames ( if was cut on B frame immediately before the I frame) or "still" frames in all other cuts with smart render in VS 11+.
After using VS 11+ and smart render for the final composition I ran the video thru VideoReDo. Fortunately VideoRedo has a Quickstream Fix function which seems to remove these post transition "still frame" artefacts. (but videoredo was unable to remove the distorted frames artefact)
I know many have said that MPEG is not ideal for editing because of its GOP structure. VS's smart render is perhaps more appropriate for non mpeg editing.
Some individuals are forced to use MPEG to edit as this is the camera's or HDTV 's native mode. A complicated workflow is required with extra software if VS is used to edit MPEG2 video and add transitions with smart render involved in the final transcode..
Seems odd that this problem has not been documented before. Perhaps most peoples final MPEG2 --> MPEG2 transcode doesn't involve going from non rendered segments to rendered segments even with smart render turned on and thus the problem would not be observed?
I first noticed this when using Sektionschef's test.mpg
If you cut on frame at 3:21 using VS or another MPEG editor such as VideoRedo (3:21 on test.mpg is an I-frame) and put a transition ( I used 1 sec fade to black) and then smart render using VS there is a movement artefact seen at 4:05 - 4:09. There are 5 frames at this point that are all the same and it comes across as a movment artefact when the clip is played. It is more noticeable in some players compared to others. And obviously less noticeable if there is minimal movement in the scene. I couldn't see the stumble in Virtualdub or VideoRedo but it was obvious in PowerDVD, WMP, Media Player Classic. The "still" frames were most obvious if you enlarge the preview screen on VS 11+ and step thru the frames one by one at 4:04 to 4:09. It is almost as if these extra frames are used as padding - perhaps to complete a GOP?
I tried this with HD MPEG2 from my Sony HC3 and confirmed that even cutting on I Frames doesn't allow VS smart render to produce transitions without the introduction of an artefact.
I examined the GOP structure of my HD MPEG2. There are 12 frames from I-frame to I-frame. Cutting on the B frame prior to the I-frame produced the distorted frames. Cutting on any other frames produced the segment of "still" frames". The segment of still frames varied from about 5 frames near the I-frame down to 2 frames away from the I-Frame.
I have yet to confirm that this movement artefact happens with all transitions and cuts when editing with VS, but all the single 22 cuts I produced at different times in the same 10 sec segment of HD MPEG from my Sony HC3 all had either the distorted frames ( if was cut on B frame immediately before the I frame) or "still" frames in all other cuts with smart render in VS 11+.
After using VS 11+ and smart render for the final composition I ran the video thru VideoReDo. Fortunately VideoRedo has a Quickstream Fix function which seems to remove these post transition "still frame" artefacts. (but videoredo was unable to remove the distorted frames artefact)
I know many have said that MPEG is not ideal for editing because of its GOP structure. VS's smart render is perhaps more appropriate for non mpeg editing.
Some individuals are forced to use MPEG to edit as this is the camera's or HDTV 's native mode. A complicated workflow is required with extra software if VS is used to edit MPEG2 video and add transitions with smart render involved in the final transcode..
Seems odd that this problem has not been documented before. Perhaps most peoples final MPEG2 --> MPEG2 transcode doesn't involve going from non rendered segments to rendered segments even with smart render turned on and thus the problem would not be observed?