ffmpeg - How to transcode video stream by changing only the resolution? -


i transcode video stream using ffmpeg tool , change video stream resolution, i.e. video , audio parameters should remain same.

according man page of ffmpeg following command line should provide desired result:

ffmpeg -i input.mp4 -vcodec copy -acodec copy -s wxh output.avi

the video codec of input stream compatible avi container.

the actual result resolution remains unchanged , seems stream repacked in avi container.

the resolution of output stream changed without -vcodec copy option, video codec changed: h264 (constrained baseline) - > mpeg4 (simple profile).

when copy video stream, cannot change of paramters, since… well, you're copying it. ffmpeg won't touch in way, can't change dimensions, frame rate, et cetera.

also, ffmpeg chooses default video codec if don't specify one. avi files, that's mpeg4.

if want h.264 video, choose -c:v libx264 instead (or -vcodec libx264 same). if need keep original profile, use -profile:v baseline.

two things:

  • when change size, recode video. lowers quality , might considerably harm video. compensate this, might need set higher quality level. setting constant rate factor below default of 23, e.g. -crf 20. experiment , see how video looks like. if have time, add -preset slow (or slower, veryslow), give better compression.

  • not matters in case, since input uses constrained baseline profile, note h.264 in avi not supported, @ least when using b pictures. baseline doesn't support b pictures though, should fine. happen file can't played on devices or players if use main profile or above. rather mux mp4 or mkv container, if input file mp4 anyway.


Comments

Post a Comment

Popular posts from this blog

php - Why I am getting the Error "Commands out of sync; you can't run this command now" -

the documentation of error mentioned in title says if commands out of sync; can't run command now in client code, calling client functions in wrong order. this can happen, example, if using mysql_use_result() , try execute new query before have called mysql_free_result(). can happen if try execute 2 queries return data without calling mysql_use_result() or mysql_store_result() in between. from here: http://dev.mysql.com/doc/refman/5.0/en/commands-out-of-sync.html but in first query not fetching data mysql database, inserting. , in second query getting data database. here code $connection = mysqli_connect("localhost","username","password","tbl_msgs"); if(mysqli_connect_errno($connection)) { die("failed connect mysql: " . mysqli_connect_error()); } $query = "insert users (total_comments, total_views) values ({$total_comments}, {$total_views});"; $query .= "insert msgs (no...
Read more

linux - Does gcc have any options to add version info in ELF binary file? -

i mean whether gcc can insert source code version infor elf binary section or similar. not want change source file, add info gcc option in makefile. you can emit version info text file, turn text file object file statically link executable. the first step simple have write code: script or write version info in format plain text file. write makefile rule produce version.o version.txt, using objcopy . you'll have object file 2 useful symbols defined in it: beginning , end of textual version info. add generated object executable, , you'll able access version 2 ways: running strings on binary, or writing code in application print version string (you'll need declare start , end symbols variables in header file).
Read more

java - Are there any classes that implement javax.persistence.Parameter<T>? -

i'm using named queries fetch entities database using jpa , hibernate , came across puzzling me: how come there no default implementations of javax.persistence.parameter interface? i rather impressed how @staticmetamodel used criteriabuilder in jpa2 meaning type safety , don't have mess around setting string names. wanted apply similar of jpa1 ejb's i'm working on: dealergroup_.class: public dealergroup_ { public parameter<integer> id = new parameterimpl<integer>("id"); /// etc... } dealergroupfacade.class: // ... public dealergroup fetch(integer id) { typedquery<dealergroup> query = em.createnamedquery("dealergroup.fetchbyid", dealergroup.class); query.setparameter(dealergroup_.id, query); return query.getsingleresult(); } // ... i surprised find there no implementations of parameter interface - of course, implement myself absence makes me suspicious may mistake using in way? should implementing parameter...
Read more