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#1
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can videos change resolution/aspect ratio mid-stream?
Reading a post (from Paul) in the "What software is used to edit MP4
videos?" thread (in the XP 'group), reminded me to wonder something I've been wondering for some time: Can a video file change resolution part way through? I'm not talking about where it is all at the highest resolution and parts are "letterboxed", "pillarboxed", or "postage-stamped", i. e. don't fill the frame but the rest is filled with black (or other colour, or even patterned!), but a genuine change of resolution. Or, I suppose, other parameters - frame rate, colour depth (or colour/monochrome), number of soundtracks, or probably other things I haven't thought of. If it can, do any of the editors in common use handle such a transition? I was, among other things, wondering what happens if you splice together two segments (which I think most of the editors can do) that have different resolutions/aspect ratios. (If the answer is yes they can, I expect it's only some video formats?) -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf I like to think of her as Mary Poppins's evil twin - Michelle Gomez, on the character "Missy" (female version of the Master?) she plays in Doctor Who [RT 2017/6/24-30] |
#2
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can videos change resolution/aspect ratio mid-stream?
On 16/03/2019 11:40, J. P. Gilliver (John) wrote:
Can a video file change resolution part way through? Unfortunately, yes, and it's a f*ker to deal with if you want to keep a program whose content is decent but it's been poorly put together, so as to do that. Firstly, videos recorded by some PVRs can do this *by design*, for exanple some of the Panasonic DMR series. If you plan to copy recordings from these machines to your PC for processing into DVDs or conventional video formats such as mkv or mp4, you'd probably best disable this setting - certainly for DVDs you *must* do so: http://www.macfh.co.uk/JavaJive/Audi...C.html#setting But too often it happens by cock-up of the broadcaster. I've recently been going through my old Dreambox, Panasonic DMR, and VCR recordings and have found a number of examples of this (most of them were actually switches in aspect ratio rather than actual changes in resolution, but the difficulties seem to be much the same in both cases). I can remember for example ... 'Life In The Freezer - 1 Bountiful Sea' began in widescreen, but at 5:08 somebody realised the mistake and corrected it to its original 4:3. Unfortunately, I couldn't find a way of correcting this seamlessly - I had to split the file into two at that point, process the two parts differently, then join them together again, with the result that there is a glitch at the point of the join. Several episodes of 'The Singing Detective' had widescreen leading titles, before switching to 4:3 for the actual content. However this was easier to deal with, because the two parts were separated by a silent blank screen. Then, of course, there are the ad-breaks in programmes or films shown on commercial channels, but, although it can be tedious trying to find the right point at which to edit, because sometimes the sound or picture cross fades between the two, in the long run, because you don't want to keep the ads, it's a matter of choice where to cut. Also, some transport streams and formats allow finer editing control than others - for example it can be very difficult to edit an mp4 as accurately as desired to preserve just the part you want because inevitably the available cut point are either too early or too late. |
#3
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can videos change resolution/aspect ratio mid-stream?
In message , Java Jive
writes: On 16/03/2019 11:40, J. P. Gilliver (John) wrote: Can a video file change resolution part way through? Unfortunately, yes, and it's a f*ker to deal with if you want to keep a program whose content is decent but it's been poorly put together, so as to do that. Firstly, videos recorded by some PVRs can do this *by design*, for exanple some of the Panasonic DMR series. If you plan to copy Ah, I hadn't thought of videos recorded off-air, where the broadcasters change what they're putting out, as they do at least between prog.s and often do for the ad. breaks. [rest snipped - interesting, thanks.] -- J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf "You _are_ Zaphod Beeblebrox? _The_ Zaphod Beeblebrox?" "No, just _a_ Zaphod Beeblebrox. I come in six-packs." (from the link episode) |
#4
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can videos change resolution/aspect ratio mid-stream?
J. P. Gilliver (John) wrote:
Reading a post (from Paul) in the "What software is used to edit MP4 videos?" thread (in the XP 'group), reminded me to wonder something I've been wondering for some time: Can a video file change resolution part way through? I'm not talking about where it is all at the highest resolution and parts are "letterboxed", "pillarboxed", or "postage-stamped", i. e. don't fill the frame but the rest is filled with black (or other colour, or even patterned!), but a genuine change of resolution. Or, I suppose, other parameters - frame rate, colour depth (or colour/monochrome), number of soundtracks, or probably other things I haven't thought of. If it can, do any of the editors in common use handle such a transition? I was, among other things, wondering what happens if you splice together two segments (which I think most of the editors can do) that have different resolutions/aspect ratios. (If the answer is yes they can, I expect it's only some video formats?) The quickest way I could answer this, is to look at the format specification for a "container". Like this AVI spec: https://web.archive.org/web/20171211...8.com/avi.html There's only one header per file, that I can see there. And that is where the width and height are. There are multiple container formats (.mov, .mp4, .mkv, .avi), and they don't necessarily all have to work the same way. But it helps... You would have to go through the syntax spec for each container design, and see if multiple header chunks are allowed. And remember that your video has to play both forwards and backwards (for jog and shuttle). The first segment could end in mid-GOP, followed by a second segment of a different WxH. Now, play that mess backwards. Can you imagine the mayhem this would cause ? Or, imagine the user selected "full screen" for video playback, then the movie res changes after the first scene. What happens ? Eww. I think it's easier to bring all the videos to a common resolution before rendering them. The video render resolution does not have to be equal to the resolution of the frames. I can be editing a 1920x1080 video, and render out to 1280x720 to save on bitrate and file size. So all the segments originally recorded at some other values, could end up being converted to 1280x720 when my final video out is made. And the video just looks a bit more fuzzy, the smaller the output render resolution happens to be. If I render to 160x120, I save a ton of file size, and the video looks terrible :-) And when I use my "player" later, it will automatically up-scale to mostly fill my screen. Rather than obediently play at 160x120 in a tiny little window. Paul |
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