avformat: Add av_mime_codec_str public API

Add a public API for producing RFC 4281/6381 codecs trings for
MIME types.

This can be required for providing alternative video files to
a web browser, letting the browser pick the best file it supports.
Such strings also allow querying a browser whether it supports
a certain codec combination.

Finally, if implementing a DASH/HLS segmenter outside of libavformat,
one also has to generate such strings.

Generating such strings for H264/AAC is very simple, but for
more modern codecs, it can require a lot of nontrivial codec
specific parsing of extradata.

As libavformat already implements this, expose it for users as well.

The old, internal function ff_make_codec_str is kept and used by
the HLS and DASH muxers; the old function takes a logging context
which can be used for logging auxillary info about how the string
generation worked out.

doc/APIchanges

@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
 
 API changes, most recent first:
 
+2025-12-xx - xxxxxxxxxx - lavf 62.x.xxx - avformat.h
+  Add av_mime_codec_str
+
 2025-12-xx - xxxxxxxxxx - lavu 60.20.100 - hwcontext_vulkan.h
   Add av_vk_get_optional_instance_extensions().
   Add av_vk_get_optional_device_extensions().

libavformat/Makefile

@@ -7,9 +7,11 @@ HEADERS = avformat.h                                                    \
           version_major.h                                               \
 
 OBJS = allformats.o         \
+       av1.o                \
        avformat.o           \
        avio.o               \
        aviobuf.o            \
+       codecstring.o        \
        demux.o              \
        demux_utils.o        \
        dump.o               \
@@ -21,6 +23,7 @@ OBJS = allformats.o         \
        metadata.o           \
        mux.o                \
        mux_utils.o          \
+       nal.o                \
        options.o            \
        os_support.o         \
        protocols.o          \
@@ -31,12 +34,13 @@ OBJS = allformats.o         \
        urldecode.o          \
        utils.o              \
        version.o            \
+       vpcc.o               \
 
 OBJS-$(HAVE_LIBC_MSVCRT)                 += file_open.o
 
 # subsystems
 OBJS-$(CONFIG_ISO_MEDIA)                 += isom.o
-OBJS-$(CONFIG_ISO_WRITER)                += av1.o avc.o hevc.o nal.o vvc.o vpcc.o
+OBJS-$(CONFIG_ISO_WRITER)                += avc.o hevc.o vvc.o
 OBJS-$(CONFIG_IAMFDEC)                   += iamf_reader.o iamf_parse.o iamf.o
 OBJS-$(CONFIG_IAMFENC)                   += iamf_writer.o iamf.o
 OBJS-$(CONFIG_NETWORK)                   += network.o
@@ -179,7 +183,7 @@ OBJS-$(CONFIG_CONCAT_DEMUXER)            += concatdec.o
 OBJS-$(CONFIG_CRC_MUXER)                 += crcenc.o
 OBJS-$(CONFIG_DATA_DEMUXER)              += rawdec.o
 OBJS-$(CONFIG_DATA_MUXER)                += rawenc.o
-OBJS-$(CONFIG_DASH_MUXER)                += dash.o dashenc.o hlsplaylist.o codecstring.o
+OBJS-$(CONFIG_DASH_MUXER)                += dash.o dashenc.o hlsplaylist.o
 OBJS-$(CONFIG_DASH_DEMUXER)              += dash.o dashdec.o
 OBJS-$(CONFIG_DAUD_DEMUXER)              += dauddec.o
 OBJS-$(CONFIG_DAUD_MUXER)                += daudenc.o
@@ -267,7 +271,7 @@ OBJS-$(CONFIG_HEVC_MUXER)                += rawenc.o
 OBJS-$(CONFIG_EVC_DEMUXER)               += evcdec.o rawdec.o
 OBJS-$(CONFIG_EVC_MUXER)                 += rawenc.o
 OBJS-$(CONFIG_HLS_DEMUXER)               += hls.o hls_sample_encryption.o
-OBJS-$(CONFIG_HLS_MUXER)                 += hlsenc.o hlsplaylist.o codecstring.o
+OBJS-$(CONFIG_HLS_MUXER)                 += hlsenc.o hlsplaylist.o
 OBJS-$(CONFIG_HNM_DEMUXER)               += hnm.o
 OBJS-$(CONFIG_HXVS_DEMUXER)              += hxvs.o
 OBJS-$(CONFIG_IAMF_DEMUXER)              += iamfdec.o
@@ -634,7 +638,7 @@ OBJS-$(CONFIG_WAV_DEMUXER)               += wavdec.o pcm.o
 OBJS-$(CONFIG_WAV_MUXER)                 += wavenc.o
 OBJS-$(CONFIG_WC3_DEMUXER)               += wc3movie.o
 OBJS-$(CONFIG_WEBM_MUXER)                += matroskaenc.o matroska.o \
-                                            av1.o avlanguage.o
+                                            avlanguage.o
 OBJS-$(CONFIG_WEBM_DASH_MANIFEST_MUXER)  += webmdashenc.o
 OBJS-$(CONFIG_WEBM_CHUNK_MUXER)          += webm_chunk.o
 OBJS-$(CONFIG_WEBP_MUXER)                += webpenc.o

libavformat/avformat.h

@@ -2890,6 +2890,21 @@ int av_match_ext(const char *filename, const char *extensions);
 int avformat_query_codec(const AVOutputFormat *ofmt, enum AVCodecID codec_id,
                          int std_compliance);
 
+struct AVBPrint;
+/**
+ * Make a RFC 4281/6381 like string describing a codec for MIME types.
+ *
+ * @param par pointer to an AVCodecParameters struct describing the codec
+ * @param frame_rate an AVRational for the frame rate, for deciding the
+ *                   right profile for video codecs. Pass an invalid
+ *                   AVRational (1/0) to indicate that it is unknown.
+ * @param str the output string buffer
+ * @param size the size of the string pointed to by str
+ * @return <0 on error
+ */
+int av_mime_codec_str(const AVCodecParameters *par,
+                      AVRational frame_rate, struct AVBPrint *out);
+
 /**
  * @defgroup riff_fourcc RIFF FourCCs
  * @{

libavformat/codecstring.c

@@ -220,3 +220,9 @@ int ff_make_codec_str(void *logctx, const AVCodecParameters *par,
     }
     return 0;
 }
+
+int av_mime_codec_str(const AVCodecParameters *par,
+                      AVRational frame_rate, struct AVBPrint *out)
+{
+    return ff_make_codec_str(NULL, par, &frame_rate, out);
+}

libavformat/version.h

@@ -31,8 +31,8 @@
 
 #include "version_major.h"
 
-#define LIBAVFORMAT_VERSION_MINOR   6
-#define LIBAVFORMAT_VERSION_MICRO 103
+#define LIBAVFORMAT_VERSION_MINOR   7
+#define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \