XvQueryEncodings(3)

💖 XvQueryEncodings — bestie, let's go get the encoding list 💖

okay so picture this: you're deep in libXv (that's the X Video extension library, the one that lives in X11/extensions/Xvlib.h), and you need to know every encoding an adaptor supports. That's literally what XvQueryEncodings(3) does. She's a libXv function, she's a queen, and she's about to hand you the whole list. 👑

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✨ SYNOPSIS ✨

#include <X11/extensions/Xvlib.h>

int XvQueryEncodings(Display *dpy, XvPortID port,
                     unsigned int *p_num_encodings,
                     XvEncodingInfo **pp_encoding_info);

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🌸 ARGUMENTS 🌸

• dpy — the connection to the X server. Your lil lifeline to the server, bestie. 🫶
• port — the port whose adaptor we're interrogating about its list of encodings.
• p_num_encodings — a pointer to where the number of encodings supported by the adaptor gets written. So after this call, that's your count. 📝
• pp_encoding_info — a pointer to where the list of returned encoding information is returned. And XvEncodingInfo has this exact structure:

typedef struct {
  XvEncodingID encoding_id;
  char *name;
  unsigned long width;
  unsigned long height;
  XvRational rate;
  unsigned long num_encodings;
} XvEncodingInfo;

Let's break down those fields, no gatekeeping:

• encoding_id — the encoding-id of the encoding. This is the ID you use to identify an encoding when you change a port's encoding attribute. So like, remember it. 💅
• name — a pointer to a formatted string that identifies the encoding. The string has the format "timing-signaltype". For example "ntsc-composite". Cute, right? 🎀
• width,height — the width and height, in pixels, of the decoded video image.
• rate — the field rate of the decoded video.

And speaking of rate — the XvRational structure is what specifies a fractional number. It looks like this:

typedef struct {
  int numerator;
  int denominator;
} XvRational;

The numerator and denominator fields specify the appropriate parts of a fractional number. Math but make it slay. 🧮✨

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🌈 DESCRIPTION 🌈

XvQueryEncodings(3) returns encoding information about an adaptor. Each encoding is described by the XvEncodingInfo structure we just went over up there. The encodings are identified by an encoding-id, which you can use to set or get the encoding attribute of a port. So basically: ask once, get the whole menu, then reference stuff by ID forever. main character behavior fr fr. 👑

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💀 RETURN VALUES 💀

• [Success] — returned if XvQueryEncodings(3) completed successfully. we love a happy ending. 🥳
• [XvBadExtension] — returned if the Xv extension is unavailable. not the extension ghosting you 😭
• [XvBadAlloc] — returned if XvQueryEncodings(3) failed to allocate memory to process the request. rip, the memory said no. 💀

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🚨 DIAGNOSTICS 🚨

• [XvBadPort] — generated if the requested port does not exist. bestie. that port is not real. check your port ID. 🙈

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👀 SEE ALSO 👀

• XvFreeEncodingInfo(3)

lowkey important: there's a whole other function for freeing this encoding info, so don't just vibe and forget about it. iykyk. 🦋

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and that's the whole page, bestie!! this was XvQueryEncodings(3) from the libXv Functions crew — X Version 11, libXv 1.0.13. go query some encodings, hydrate, and free your encoding info afterwards. periodt. 💅💖✨