avf: introduce nobuffer option

Useful in cases where a significant analyzeduration is
still needed, while minimizing buffering before output.

An example is processing low-latency streams where all
media types won't necessarily come in if the
analyzeduration is small.

Additional changes by Josh Allmann <joshua.allmann@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2011-04-18
 
 API changes, most recent first:
 
+2012-07-xx - xxxxxxx - lavf 54.13.0 - avformat.h
+  Add AVFMT_FLAG_NOBUFFER for low latency use cases.
+
 2012-07-xx - xxxxxxx - lavfi 3.0.0 - avfilter.h
   Add avfilter_unref_bufferp().
 

libavformat/avformat.h

@@ -887,6 +887,7 @@ typedef struct AVFormatContext {
 #define AVFMT_FLAG_IGNDTS       0x0008 ///< Ignore DTS on frames that contain both DTS & PTS
 #define AVFMT_FLAG_NOFILLIN     0x0010 ///< Do not infer any values from other values, just return what is stored in the container
 #define AVFMT_FLAG_NOPARSE      0x0020 ///< Do not use AVParsers, you also must set AVFMT_FLAG_NOFILLIN as the fillin code works on frames and no parsing -> no frames. Also seeking to frames can not work if parsing to find frame boundaries has been disabled
+#define AVFMT_FLAG_NOBUFFER     0x0040 ///< Do not buffer frames when possible
 #define AVFMT_FLAG_CUSTOM_IO    0x0080 ///< The caller has supplied a custom AVIOContext, don't avio_close() it.
 #define AVFMT_FLAG_DISCARD_CORRUPT  0x0100 ///< Discard frames marked corrupted
 

libavformat/options_table.h

@@ -40,6 +40,7 @@ static const AVOption options[]={
 {"noparse", "disable AVParsers, this needs nofillin too", 0, AV_OPT_TYPE_CONST, {.dbl = AVFMT_FLAG_NOPARSE }, INT_MIN, INT_MAX, D, "fflags"},
 {"igndts", "ignore dts", 0, AV_OPT_TYPE_CONST, {.dbl = AVFMT_FLAG_IGNDTS }, INT_MIN, INT_MAX, D, "fflags"},
 {"discardcorrupt", "discard corrupted frames", 0, AV_OPT_TYPE_CONST, {.dbl = AVFMT_FLAG_DISCARD_CORRUPT }, INT_MIN, INT_MAX, D, "fflags"},
+{"nobuffer", "reduce the latency introduced by optional buffering", 0, AV_OPT_TYPE_CONST, {.dbl = AVFMT_FLAG_NOBUFFER }, 0, INT_MAX, D, "fflags"},
 {"analyzeduration", "how many microseconds are analyzed to estimate duration", OFFSET(max_analyze_duration), AV_OPT_TYPE_INT, {.dbl = 5*AV_TIME_BASE }, 0, INT_MAX, D},
 {"cryptokey", "decryption key", OFFSET(key), AV_OPT_TYPE_BINARY, {.dbl = 0}, 0, 0, D},
 {"indexmem", "max memory used for timestamp index (per stream)", OFFSET(max_index_size), AV_OPT_TYPE_INT, {.dbl = 1<<20 }, 0, INT_MAX, D},

libavformat/utils.c

@@ -2383,9 +2383,14 @@ int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
             break;
         }
 
-        pkt= add_to_pktbuf(&ic->packet_buffer, &pkt1, &ic->packet_buffer_end);
+        if (ic->flags & AVFMT_FLAG_NOBUFFER) {
+            pkt = &pkt1;
+        } else {
+            pkt = add_to_pktbuf(&ic->packet_buffer, &pkt1,
+                                &ic->packet_buffer_end);
             if ((ret = av_dup_packet(pkt)) < 0)
                 goto find_stream_info_err;
+        }
 
         read_size += pkt->size;
 

libavformat/version.h

@@ -30,8 +30,8 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFORMAT_VERSION_MAJOR 54
-#define LIBAVFORMAT_VERSION_MINOR 12
-#define LIBAVFORMAT_VERSION_MICRO  1
+#define LIBAVFORMAT_VERSION_MINOR 13
+#define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \