Hi Moritz, thanks for the response.
I will certainly check out the vstack method and report back. Due to
our specific use case, it may not be an option for us (we need the
combined video in a horizontal format). I'll also attempt a scale
filter as well.
When I converted from the original webm to mp4, I simply used
./ffmpeg -i a.webm a.mp4, so I believe the answer is: I am re-encoding.
Oddly, I still do get the frame size change notices, but it doesn't seem
to make any difference when I combine the mp4s to the final webm target.
On 11/24/2015 7:38 AM, Moritz Barsnick wrote:
Hi Mike,
On Mon, Nov 23, 2015 at 22:56:08 -0600, Mike Grommet wrote:
During the playback of the combined file, The right side video appears
to zoom in to the top left of itself two times. The originals appear
fine when played individually.
Interesting that the latter should happen. I would (personally, not
suggesting to) inspect each frame of both files with ffprobe.
I assume it has something to do with these messages from the ffmpeg
run:
Input stream #0:0 frame changed from size:640x480 fmt:yuv420p to size:480x360
fmt:yuv420p
Input stream #0:0 frame changed from size:480x360 fmt:yuv420p to size:320x240
fmt:yuv420p
That seems likely. :)
I also attempted a different way to merge the files (See Alternative
Command), and it has the same issue.
Firstly, you may want to use the vstack filter for this very purpose,
it saves you a lot of filter syntax:
https://ffmpeg.org/ffmpeg-filters.html#vstack
Of course, as it notes, "[all] streams must be of same pixel format and
of same width."
That said, and considering the weird size jumps in the input: Have you
considered just inserting a scale filter to force the original size?
Something like
$ ./ffmpeg -i a.webm -i b.webm -filter_complex "[0:v]scale=640:480[left];
[1:v]scale=640:480[right]; [left][right]vstack[out] -map [out] -map 0:a -map 1:a
c.webm
Additional note: As an experiment, If I first convert the original
.webm files to .mp4, combine these files together with a .webm final
target, I don't experience this problem. This might be an option, but
it seems to be an awfully hacky solution.
Even more interesting. Are you re-encoding or just remuxing ("-c
copy")?
Cheers,
Moritz
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