avcodec.h: Clarify AVCodecContext::pix_fmt documentation since its value may be set by the demuxer

rawdec.c: Only perform bits_per_coded_sample -> pix_fmt guesswork if pix_fmt hasn't been set

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@23561 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/avcodec.h

@@ -1121,8 +1121,10 @@ typedef struct AVCodecContext {
 
     /**
      * Pixel format, see PIX_FMT_xxx.
+     * May be set by the demuxer if known from headers.
+     * May be overriden by the decoder if it knows better.
      * - encoding: Set by user.
-     * - decoding: Set by libavcodec.
+     * - decoding: Set by user if known, overridden by libavcodec if known
      */
     enum PixelFormat pix_fmt;
 

libavcodec/rawdec.c

@@ -77,7 +77,7 @@ static av_cold int raw_init_decoder(AVCodecContext *avctx)
         avctx->pix_fmt = find_pix_fmt(pix_fmt_bps_mov, avctx->bits_per_coded_sample);
     else if (avctx->codec_tag)
         avctx->pix_fmt = find_pix_fmt(ff_raw_pix_fmt_tags, avctx->codec_tag);
-    else if (avctx->bits_per_coded_sample)
+    else if (avctx->pix_fmt == PIX_FMT_NONE && avctx->bits_per_coded_sample)
         avctx->pix_fmt = find_pix_fmt(pix_fmt_bps_avi, avctx->bits_per_coded_sample);
 
     context->length = avpicture_get_size(avctx->pix_fmt, avctx->width, avctx->height);