ffmpeg: accept + prefix to -pix_fmt option to disable automatic conversions.

Changelog

@@ -29,6 +29,7 @@ version next:
 - add libavresample audio conversion library for compatibility
 - MicroDVD decoder
 - Avid Meridien (AVUI) decoder
+- accept + prefix to -pix_fmt option to disable automatic conversions.
 
 
 version 0.10:

doc/ffmpeg.texi

@@ -418,6 +418,14 @@ also sources and sinks).  This is an alias for @code{-filter:v}.
 @item -pix_fmt[:@var{stream_specifier}] @var{format} (@emph{input/output,per-stream})
 Set pixel format. Use @code{-pix_fmts} to show all the supported
 pixel formats.
+If the selected pixel format can not be selected, ffmpeg will print a
+warning and select the best pixel format supported by the encoder.
+If @var{pix_fmt} is prefixed by a @code{+}, ffmpeg will exit with an error
+if the requested pixel format can not be selected, and automatic conversions
+inside filter graphs are disabled.
+If @var{pix_fmt} is a single @code{+}, ffmpeg selects the same pixel format
+as the input (or graph output) and automatic conversions are disabled.
+
 @item -sws_flags @var{flags} (@emph{input/output})
 Set SwScaler flags.
 @item -vdt @var{n}

ffmpeg.c

@@ -319,6 +319,7 @@ typedef struct OutputStream {
     int copy_initial_nonkeyframes;
 
     enum PixelFormat pix_fmts[2];
+    int keep_pix_fmt;
 } OutputStream;
 
 
@@ -706,6 +707,15 @@ static enum PixelFormat choose_pixel_fmt(AVStream *st, AVCodec *codec, enum Pixe
 
 static char *choose_pixel_fmts(OutputStream *ost)
 {
+    if (ost->keep_pix_fmt) {
+        if (ost->filter)
+            avfilter_graph_set_auto_convert(ost->filter->graph->graph,
+                                            AVFILTER_AUTO_CONVERT_NONE);
+        if (ost->st->codec->pix_fmt == PIX_FMT_NONE)
+            return NULL;
+        ost->pix_fmts[0] = ost->st->codec->pix_fmt;
+        return ost->pix_fmts;
+    }
     if (ost->st->codec->pix_fmt != PIX_FMT_NONE) {
         return av_strdup(av_get_pix_fmt_name(choose_pixel_fmt(ost->st, ost->enc, ost->st->codec->pix_fmt)));
     } else if (ost->enc->pix_fmts) {
@@ -835,6 +845,10 @@ static int configure_video_filters(FilterGraph *fg)
             return ret;
     }
 
+    if (ost->keep_pix_fmt)
+        avfilter_graph_set_auto_convert(fg->graph,
+                                        AVFILTER_AUTO_CONVERT_NONE);
+
     if ((ret = avfilter_graph_config(fg->graph, NULL)) < 0)
         return ret;
 
@@ -4661,6 +4675,11 @@ static OutputStream *new_video_stream(OptionsContext *o, AVFormatContext *oc, in
 
         video_enc->bits_per_raw_sample = frame_bits_per_raw_sample;
         MATCH_PER_STREAM_OPT(frame_pix_fmts, str, frame_pix_fmt, oc, st);
+        if (frame_pix_fmt && *frame_pix_fmt == '+') {
+            ost->keep_pix_fmt = 1;
+            if (!*++frame_pix_fmt)
+                frame_pix_fmt = NULL;
+        }
         if (frame_pix_fmt && (video_enc->pix_fmt = av_get_pix_fmt(frame_pix_fmt)) == PIX_FMT_NONE) {
             av_log(NULL, AV_LOG_FATAL, "Unknown pixel format requested: %s.\n", frame_pix_fmt);
             exit_program(1);