lavf/mux: add avformat_init_output

This allows a consumer to run the muxer's init function without actually
writing the header, which is useful in chained muxers that support
automatic bitstream filtering.

1 files changed, 32 insertions, 2 deletions

diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 057f8c58aa..82ca7277ae 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -618,6 +618,8 @@ typedef struct AVOutputFormat {
      * AVStream parameters that need to be set before packets are sent.
      * This method must not write output.
      *
+     * Return 0 if streams were fully configured, 1 if not, negative AVERROR on failure
+     *
      * Any allocations made here must be freed in deinit().
      */
     int (*init)(struct AVFormatContext *);
@@ -2374,6 +2376,10 @@ void avformat_close_input(AVFormatContext **s);
  * @addtogroup lavf_encoding
  * @{
  */
+
+#define AVSTREAM_INIT_IN_WRITE_HEADER 0 ///< stream parameters initialized in avformat_write_header
+#define AVSTREAM_INIT_IN_INIT_OUTPUT  1 ///< stream parameters initialized in avformat_init_output
+
 /**
  * Allocate the stream private data and write the stream header to
  * an output media file.
@@ -2385,14 +2391,38 @@ void avformat_close_input(AVFormatContext **s);
  *                 On return this parameter will be destroyed and replaced with a dict containing
  *                 options that were not found. May be NULL.
  *
- * @return 0 on success, negative AVERROR on failure.
+ * @return AVSTREAM_INIT_IN_WRITE_HEADER on success if the codec had not already been fully initialized in avformat_init,
+ *         AVSTREAM_INIT_IN_INIT_OUTPUT  on success if the codec had already been fully initialized in avformat_init,
+ *         negative AVERROR on failure.
  *
- * @see av_opt_find, av_dict_set, avio_open, av_oformat_next.
+ * @see av_opt_find, av_dict_set, avio_open, av_oformat_next, avformat_init_output.
  */
 av_warn_unused_result
 int avformat_write_header(AVFormatContext *s, AVDictionary **options);
 
 /**
+ * Allocate the stream private data and initialize the codec, but do not write the header.
+ * May optionally be used before avformat_write_header to initialize stream parameters
+ * before actually writing the header.
+ * If using this function, do not pass the same options to avformat_write_header.
+ *
+ * @param s Media file handle, must be allocated with avformat_alloc_context().
+ *          Its oformat field must be set to the desired output format;
+ *          Its pb field must be set to an already opened AVIOContext.
+ * @param options  An AVDictionary filled with AVFormatContext and muxer-private options.
+ *                 On return this parameter will be destroyed and replaced with a dict containing
+ *                 options that were not found. May be NULL.
+ *
+ * @return AVSTREAM_INIT_IN_WRITE_HEADER on success if the codec requires avformat_write_header to fully initialize,
+ *         AVSTREAM_INIT_IN_INIT_OUTPUT  on success if the codec has been fully initialized,
+ *         negative AVERROR on failure.
+ *
+ * @see av_opt_find, av_dict_set, avio_open, av_oformat_next, avformat_write_header.
+ */
+av_warn_unused_result
+int avformat_init_output(AVFormatContext *s, AVDictionary **options);
+
+/**
  * Write a packet to an output media file.
  *
  * This function passes the packet directly to the muxer, without any buffering